What does engine oil do besides lubricate?

It cools, by carrying heat from pistons, bearings, and cylinder walls to the sump, tank, or oil cooler. It cleans, by picking up carbon and metal particles and delivering them to the filter or screen. It seals the gap between piston rings and cylinder walls, cushions shock loads on gears and bearings, and leaves a film that protects internal surfaces from corrosion when the engine sits.

Where is the oil stored in a dry-sump engine?

In a separate oil tank mounted outside the engine, not in the crankcase. A pressure pump draws from that tank and feeds the engine, and one or more scavenge pumps pull oil out of the sump and return it to the tank. The tank includes expansion space above the oil for foaming and thermal expansion, so it is never filled to the very top.

Why is the scavenge pump larger than the pressure pump?

Because the oil coming back is not the same oil that went out. After being thrown around by the crankshaft, gears, and bearings, it is hot and full of entrained air, so the same weight of oil occupies noticeably more volume. Extra scavenge capacity keeps that frothy return moving out of the sump instead of accumulating where it would be churned further.

What does the oil cooler bypass valve do?

It routes oil around the cooler core instead of through it. When the oil is cold and thick at start-up, or when the core is congealed or obstructed, sending oil through the cooler would slow warm-up and could burst the core. The valve senses that condition and opens a path around the cooler, then closes it as the oil reaches normal operating temperature.

What causes high oil temperature during cruise?

Treat it as a symptom rather than an answer. Common causes are low oil quantity, so less oil absorbs the same heat, restricted cooling airflow or a blocked cooler core, a bypass valve stuck open, the wrong oil grade, or an internal problem such as a failing bearing adding friction. Check quantity and the cooling path first, then look inside.

What is the primary purpose of the oil system in a reciprocating aircraft engine?

To reduce friction between moving parts by lubricating bearing surfaces

To provide hydraulic pressure for operating the landing gear

To increase combustion temperature inside the engine cylinders

Besides lubrication, which additional function does engine oil perform in a reciprocating engine?

It carries heat away from internal engine parts

It generates the spark needed for ignition

It supplies fuel to the carburetor float bowl

In a dry-sump oil system, where is the main supply of engine oil stored?

In a separate external oil tank

In a reservoir inside the oil cooler

Which type of pump is most commonly used as the engine-driven oil pump in a reciprocating engine?

A gear-type positive-displacement pump

What is the function of the oil pressure relief valve in a lubrication system?

It limits oil pressure to a safe maximum value

It removes metal particles from the oil

It increases oil pressure during cold starts

What is the purpose of an oil cooler bypass (thermostatic) valve?

It routes oil around the cooler until the oil reaches operating temperature

It diverts oil to the cooler whenever the engine is started cold

It blocks oil flow to the bearings until pressure builds up

In a dry-sump engine, why is the scavenge pump usually built with greater capacity than the pressure pump?

Because the returning oil is aerated and occupies more volume

Because the oil tank is lower than the engine sump

Because scavenge oil is colder and therefore thicker

What does an oil temperature that is too high during normal cruise most commonly indicate?

Insufficient oil supply or a restriction in the oil cooler

Oil that is too low in viscosity for the engine

An overfilled oil tank with excess capacity

What is the function of the oil filter in a reciprocating engine lubrication system?

To remove foreign particles and contaminants from the circulating oil

To raise the temperature of the oil before it enters the bearings

To regulate the volume of oil delivered by the pressure pump

Why are the labyrinth oil seals around a turbine engine bearing chamber pressurized with air?

To ensure minimum loss of oil from the bearing chamber.

To raise the air pressure inside the gas path of the engine.

To force lubricating oil into the bearings under pressure.

In a turbine engine, the oil seals on the rotating assembly are kept oil-tight primarily by means of

pressurized sealing air directed across the seal.

a spring-loaded carbon face held by oil pressure.

a garter spring holding the seal lip in place.

A high viscosity index in a lubricating oil indicates that the oil's viscosity

will not vary greatly with changes in temperature.

will change significantly with changes in temperature.

is low when the oil is measured at high temperature.

What is a fuel-system icing inhibitor designed to prevent from freezing in turbine fuel?

The water entrained or dissolved in the fuel.

The kerosene-type fuel itself at low temperature.

The wax crystals that form within the base fuel.

What is the most likely result of operating an engine at extremely high temperatures using a lubricant the manufacturer recommends for a much lower temperature?

The oil pressure will be lower than normal.

The oil pressure will remain the same as it would at normal temperature.

The oil pressure will be higher than normal.

The lubricating oil used in a gas turbine engine is usually a

synthetic oil rated for high-temperature turbine service.

straight mineral oil of the type used in piston engines.

natural vegetable-base oil with additives.

In spectrometric oil analysis (SOAP), the oil spectrometer measures the

concentration of metallic wear particles suspended in the oil.

specific gravity of the oil sample.

contaminants present only on the surface of the oil.

When operating, a gear-type (external gear) oil pump moves oil by

carrying it in the spaces between the gear teeth and the pump casing.

carrying half around the casing and passing the other half between the gears.

forcing it through the center where the intermeshing gear teeth engage.

A scavenge filter is incorporated in a gas turbine lubrication system to

protect the pressure pump from debris carried in the returning oil.

protect the oil cooler from debris carried in the returning oil.

protect the scavenge pump from debris carried in the returning oil.

On a turbine engine showing no change in power-setting parameters but a high oil temperature, a likely cause is

distress of an engine main bearing.

excessively high scavenge pump oil flow.

turbine damage or loss of turbine efficiency.

In most turbine engines, the lubricating oil is cooled by

a fuel/oil cooler (heat exchanger).

compressor bleed air directed over the oil tank.

ram air ducted over an air/oil radiator only.

What type of filter is used to protect the oil pressure spray jets in a turbine engine lubrication system?

In-line thread-type (last-chance) filters.

A chip detector in a turbine engine oil system is a

magnetic plug installed in the scavenge (return) line.

sight window installed in the oil pump casing.

sight window installed in the oil tank.

When operating, a gerotor-type oil pump moves oil by

carrying it through the changing volumes formed by the intermeshing rotors to the outlet.

carrying half around the casing and passing the other half between the gears.

carrying it only in the space between the gear teeth and the pump casing.

In a turbine engine that uses a fuel-oil heat exchanger, the oil temperature is controlled by a thermostatic valve that regulates the flow of

oil through the heat exchanger.

fuel through the heat exchanger.

both fuel and oil through the heat exchanger.

What is the purpose of the last-chance oil filters in a turbine engine lubrication system?

To prevent clogging of the oil spray nozzles.

To filter the oil immediately before it enters the scavenge pump.

To assure a clean supply of oil to the entire lubrication system.

At cruise RPM, some oil will flow through the relief valve of a gear-type engine oil pump. This is normal because the relief valve is set at a pressure that is

lower than the pressure pump capabilities.

lower than the pump inlet pressure.

higher than the pressure pump capabilities.

After making a welded repair to a pressurized-type turbine engine oil tank, the tank should be pressure-checked to

not less than 5 PSI plus the maximum operating pressure of the tank.

not less than 5 PSI plus the average operating pressure of the tank.

not more than 5 PSI total regardless of operating pressure.

Failure-related ferrous metal particles in turbine engine oil cause an electrical-indicating type magnetic chip detector to indicate their presence by

bridging the gap between the detector center (positive) electrode and the ground electrode.

disturbing the magnetic lines of flux around the detector tip.

generating a small electric current as the particles contact the dissimilar metal of the detector tip.

What will result if an engine oil filter becomes completely blocked?

Oil will flow at the normal rate through the system.

Oil will flow at a reduced rate through the system.

Oil flow to the engine will stop completely.

A turbine engine dry-sump lubrication system of the self-contained, high-pressure design

consists of pressure, breather, and scavenge subsystems.

operates without any form of oil heat exchanger.

stores all of its oil supply in the engine crankcase.

What is the primary purpose of the hopper located in the oil supply tank of some dry-sump engine installations?

To reduce the time required to warm the oil to operating temperature.

To impart a centrifugal motion to the oil so that foreign particles separate more readily.

To reduce surface aeration of the hot oil and thereby reduce sludge and varnish formation.

What determines the minimum particle size that will be excluded by a Cuno-type (stacked-disc, edge-filtration) oil filter?

Both the number and thickness of the discs in the assembly.

A full-flow oil system has

a variable oil pressure dependent upon throttle setting.

a hot and cold oil pressure limit.

a single fixed minimum oil pressure.

A felt-type oil filter element in a turbine engine lubrication system should be

removed and replaced with a new filter element.

removed and cleaned in methyl ethyl ketone solvent.

back-flushed in place with clean engine oil.

What type of filter is generally fitted on the inlet side of a turbine engine oil scavenge pump?

A sintered-bronze cartridge filter.

A pleated-paper element filter.

The output of a vane-type oil pump is controlled by

outlet pressure acting against spring pressure.

inlet pressure acting against a check valve.

outlet pressure acting on a hydraulic servo.

In a dry-sump turbine engine oil system, the sump

is used as a collecting point only.

stores the entire oil supply for the engine.

provides direct lubrication to the main bearings.

A turbine engine gearbox breather is prevented from losing oil to the atmosphere by the action of

an impeller and centrifugal force.

a spring-loaded air/oil relief valve.

a one-way check valve in the vent line.

Engine Lubrication Systems — FAA A&P Test Questions (ACS AM.III.G)

Engine Lubrication Systems asks you to trace oil from the tank or sump, through the pump, past every valve, and back again, and to say what each component does when something goes wrong. AM.III.G questions cover what oil is actually for beyond lubrication, how wet-sump and dry-sump layouts differ, which pump type the engine drives, and what the relief, bypass, and thermostatic valves each protect. Follow one drop of oil around the whole circuit and most of this area becomes a memory of the path rather than a list.

Written by the AMTprep editorial team · Published July 27, 2026 · Last reviewed October 21, 2026

Written against the FAA primary sources cited at the foot of this page.

What ACS AM.III.G covers

This area covers reciprocating and turbine lubrication systems, their components, and the indications that reveal a problem, following the Powerplant Handbook, FAA-H-8083-32. The FAA begins with purpose. Oil primarily reduces friction between moving parts, but the test also expects the secondary jobs: carrying heat away from pistons, bearings, and cylinder walls, cleaning by carrying carbon and metal particles to the filter, sealing the small gaps between piston rings and cylinder walls, cushioning shock loads on gear teeth and bearings, and protecting internal surfaces from corrosion. Layout comes next. In a wet-sump engine the supply lives in the crankcase sump beneath the engine, while a dry-sump engine keeps the supply in a separate external tank and uses scavenge pumps to return oil there, which is the arrangement used where oil quantity is large or attitude changes are severe. The engine-driven pressure pump is normally a constant-displacement gear pump, and because it delivers more than the engine needs, an oil pressure relief valve limits maximum system pressure by returning excess oil to the pump inlet or sump. Two further valves are easy to confuse and are tested separately: the filter bypass valve routes oil around a clogged filter so the engine still gets oil, while the oil cooler bypass, or thermostatic, valve routes oil around the cooler core when the oil is cold or the core is blocked. Scavenge capacity is deliberately greater than pressure capacity, because returning oil is hot, foamy, and mixed with air, so it occupies more volume than it did on the way out. Indication questions close the area, treating a high cruise oil temperature as a symptom to be traced to oil quantity, cooling airflow, the cooler and its bypass, or internal engine condition.

Where this sits on the test

ACS AM.III.G is tested on the FAA Powerplant written test, one of 1,353 ACS-tagged questions in the Powerplant bank. Every question tagged to this area carries a worked rationale and its FAA handbook reference, so you can drill the code itself rather than the whole test.

FAA handbook references

FAA-H-8083-32

Three traps candidates fall into

Candidates size the scavenge pump smaller than the pressure pump, reasoning that the pressure side feeds the whole engine. Scavenged oil is aerated and foamy after being churned by the crankshaft and gears, so it occupies more volume, and the scavenge pump must be larger to keep the sump from filling up.
The three bypass paths get answered with one component. The pressure relief valve limits system pressure, the filter bypass sends oil around a clogged filter element, and the oil cooler bypass routes oil around the cooler when it is cold or obstructed. Each protects a different failure, and the test asks about them separately.
A dry-sump engine gets described as having no oil reservoir at all. The supply is simply not kept in the crankcase; it lives in a separate external tank, and scavenge pumps continually return oil there. Questions about where oil is stored, and about tank expansion space, hinge on knowing which layout is installed.

50 free sample questions from ACS AM.III.G

AM.III.GTap an answer
What is the primary purpose of the oil system in a reciprocating aircraft engine?
Show the answer and explanation
Answer: To reduce friction between moving parts by lubricating bearing surfaces
Why: The handbook lists several functions of engine oil, but the principal one is lubrication—forming an oil film between moving parts to reduce friction and wear. Oil also cools, cleans, seals, and cushions, but lubrication is the primary purpose. Oil does not raise combustion temperature and is not the source of landing-gear hydraulic power.· FAA-H-8083-32 — Lubricating System / Purpose of Engine Oil
AM.III.GTap an answer
Besides lubrication, which additional function does engine oil perform in a reciprocating engine?
Show the answer and explanation
Answer: It carries heat away from internal engine parts
Why: In addition to reducing friction, oil cools the engine by absorbing heat from pistons, bearings, and other internal parts and transferring it to the oil cooler. Oil also seals, cleans, and cushions, but it has no role in fuel delivery to the carburetor or in producing ignition spark.· FAA-H-8083-32 — Functions of Engine Oil (cooling, sealing, cleaning)
AM.III.GTap an answer
In a dry-sump oil system, where is the main supply of engine oil stored?
Show the answer and explanation
Answer: In a separate external oil tank
Why: A dry-sump system stores the bulk of its oil in a separate tank mounted away from the engine, and a scavenge pump returns oil from the engine sump to that tank. A wet-sump system, by contrast, keeps the oil supply in the crankcase sump. The oil cooler is a heat exchanger, not a storage reservoir.· FAA-H-8083-32 — Dry-Sump vs. Wet-Sump Systems
AM.III.GTap an answer
Which type of pump is most commonly used as the engine-driven oil pump in a reciprocating engine?
Show the answer and explanation
Answer: A gear-type positive-displacement pump
Why: The handbook identifies the gear-type pump as the most widely used oil pump in reciprocating engines. It is a positive-displacement pump in which two meshing gears carry oil around the housing and force it out under pressure. Centrifugal pumps lack positive displacement, and diaphragm pumps are typically used for fuel, not engine oil.· FAA-H-8083-32 — Oil Pumps (gear-type)
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What is the function of the oil pressure relief valve in a lubrication system?
Show the answer and explanation
Answer: It limits oil pressure to a safe maximum value
Why: The oil pressure relief valve regulates system pressure by opening to bypass excess oil back to the inlet or sump once pressure reaches a set value, protecting the system from excessive pressure. It does not boost pressure on cold starts, and metal-particle removal is the job of the oil filter, not the relief valve.· FAA-H-8083-32 — Oil Pressure Relief Valve
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What is the purpose of an oil cooler bypass (thermostatic) valve?
Show the answer and explanation
Answer: It routes oil around the cooler until the oil reaches operating temperature
Why: The thermostatic bypass valve senses oil temperature and directs cold oil around the cooler core, sending oil through the cooler only after it warms up. This helps the oil reach operating temperature quickly and keeps it within the proper range. It does not divert cold oil into the cooler, nor does it gate flow to the bearings.· FAA-H-8083-32 — Oil Cooler and Thermostatic Bypass Valve
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In a dry-sump engine, why is the scavenge pump usually built with greater capacity than the pressure pump?
Show the answer and explanation
Answer: Because the returning oil is aerated and occupies more volume
Why: Scavenged oil returning from the engine is mixed with air and foams, so it occupies a greater volume than the solid oil delivered by the pressure pump. To keep the sump clear and prevent the oil from backing up, the scavenge pump is given greater capacity. Tank position and oil viscosity are not the reasons for the larger scavenge capacity.· FAA-H-8083-32 — Scavenge Pump Capacity
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What does an oil temperature that is too high during normal cruise most commonly indicate?
Show the answer and explanation
Answer: Insufficient oil supply or a restriction in the oil cooler
Why: Excessively high oil temperature commonly results from a low oil quantity or a restriction in the cooler that prevents adequate heat removal, both of which reduce the oil's ability to carry heat away. An overfilled tank or low-viscosity oil are not the typical causes; the handbook ties high oil temperature chiefly to inadequate cooling or low supply.· FAA-H-8083-32 — Oil Temperature Indications / Troubleshooting
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What is the function of the oil filter in a reciprocating engine lubrication system?
Show the answer and explanation
Answer: To remove foreign particles and contaminants from the circulating oil
Why: The oil filter traps dirt, carbon, metal particles, and other contaminants so that clean oil reaches the bearings and other moving parts, helping prevent wear and damage. Heating the oil is not its purpose, and regulating delivered oil volume is handled by the pump and relief valve, not the filter.· FAA-H-8083-32 — Oil Filters
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A turbine engine bearing oil seal failure would most likely cause
Show the answer and explanation
Answer: high oil consumption.
Why: The bearing oil seal keeps lubricating oil within the bearing chamber. If it fails, oil escapes from the chamber, often past the seal into the gas path where it is burned, so the most likely symptom is high oil consumption rather than a pressure or temperature change (FAA-H-8083-32, Turbine Engine Lubrication).· FAA-H-8083-32 — Engine Lubrication Systems
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Why are the labyrinth oil seals around a turbine engine bearing chamber pressurized with air?
Show the answer and explanation
Answer: To ensure minimum loss of oil from the bearing chamber.
Why: Bearing chambers are sealed with air-pressurized (labyrinth) seals so that sealing air flows inward across the seal, opposing the escape of oil. Maintaining this air pressure differential keeps oil inside the chamber and reduces oil loss into the gas path. It is not used to force oil into the bearings (FAA-H-8083-32, Bearings and Seals).· FAA-H-8083-32 — Engine Lubrication Systems
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In a turbine engine, the oil seals on the rotating assembly are kept oil-tight primarily by means of
Show the answer and explanation
Answer: pressurized sealing air directed across the seal.
Why: The oil seals on the rotating assembly are air-type seals: a supply of sealing air at a pressure higher than the bearing chamber flows across the seal toward the oil, opposing oil escape. This pressurized air keeps the seal oil-tight, unlike garter springs or expander rings used in static seals.· FAA-H-8083-32 — Engine Lubrication Systems
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A high viscosity index in a lubricating oil indicates that the oil's viscosity
Show the answer and explanation
Answer: will not vary greatly with changes in temperature.
Why: Viscosity index measures how much an oil's viscosity changes with temperature. A high viscosity index means the viscosity stays comparatively stable, so it does not vary greatly with temperature change, keeping the oil neither too thick when cold nor too thin when hot.· FAA-H-8083-32 — Engine Lubrication Systems
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What is a fuel-system icing inhibitor designed to prevent from freezing in turbine fuel?
Show the answer and explanation
Answer: The water entrained or dissolved in the fuel.
Why: A fuel-system icing inhibitor acts on the small amount of water dissolved or entrained in the fuel, lowering its freezing point so it cannot form ice crystals that block filters at low temperatures. It does not stop the kerosene-type fuel itself from freezing; it targets the water in the fuel.· FAA-H-8083-32 — Engine Fuel and Fuel Metering Systems
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What is the most likely result of operating an engine at extremely high temperatures using a lubricant the manufacturer recommends for a much lower temperature?
Show the answer and explanation
Answer: The oil pressure will be lower than normal.
Why: An oil intended for a lower temperature becomes too thin when run at a much higher temperature, so its viscosity drops. The thinner oil flows and leaks past clearances more easily, producing oil pressure lower than normal and risking inadequate film strength.· FAA-H-8083-32 — Engine Lubrication Systems
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The lubricating oil used in a gas turbine engine is usually a
Show the answer and explanation
Answer: synthetic oil rated for high-temperature turbine service.
Why: Gas turbine engines normally use synthetic oils because they remain stable at the very high bearing temperatures and resist oxidation and coking far better than mineral oils. Mineral oils break down at turbine operating temperatures and are unsuitable.· FAA-H-8083-32 — Engine Lubrication Systems
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In spectrometric oil analysis (SOAP), the oil spectrometer measures the
Show the answer and explanation
Answer: concentration of metallic wear particles suspended in the oil.
Why: An oil spectrometer used in spectrometric oil analysis measures the concentration of metallic contaminants suspended and dissolved throughout the oil sample, identifying which engine components are wearing. It analyzes fine particulate and dissolved metals, not just surface debris or specific gravity.· FAA-H-8083-32 — Engine Lubrication Systems
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In a fuel/oil cooler (heat exchanger), the oil pressure is normally maintained
Show the answer and explanation
Answer: higher than the fuel pressure.
Why: In a fuel/oil cooler the oil is kept at a higher pressure than the fuel so that any internal leak passes oil into the fuel rather than fuel into the oil system. This protects the engine bearings from fuel contamination and oil dilution.· FAA-H-8083-32 — Engine Lubrication Systems
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When operating, a gear-type (external gear) oil pump moves oil by
Show the answer and explanation
Answer: carrying it in the spaces between the gear teeth and the pump casing.
Why: A gear-type external gear pump draws oil in at the inlet and traps it in the spaces between the gear teeth and the casing, carrying it around to the outlet. The meshing teeth form a seal so oil cannot pass back through the center, giving positive-displacement delivery.· FAA-H-8083-32 — Engine Lubrication Systems
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A scavenge filter is incorporated in a gas turbine lubrication system to
Show the answer and explanation
Answer: protect the pressure pump from debris carried in the returning oil.
Why: Scavenge oil returning from the bearing chambers carries any debris before it passes back to the tank and then to the pressure pump. The scavenge filter removes this debris so that the pressure pump and the downstream bearing feed jets are protected from contamination.· FAA-H-8083-32 — Engine Lubrication Systems
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On a turbine engine showing no change in power-setting parameters but a high oil temperature, a likely cause is
Show the answer and explanation
Answer: distress of an engine main bearing.
Why: If the power-setting parameters are unchanged but oil temperature is high, the extra heat is being generated by friction at a rotating part rather than in the gas path. A distressed main bearing produces this localized heating, raising oil temperature without affecting the thrust indications.· FAA-H-8083-32 — Engine Lubrication Systems
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In most turbine engines, the lubricating oil is cooled by
Show the answer and explanation
Answer: a fuel/oil cooler (heat exchanger).
Why: Turbine engine oil is usually cooled in a fuel/oil heat exchanger, where heat passes from the hot oil into the cooler fuel on its way to the burners. This simultaneously cools the oil and warms the fuel, helping prevent fuel system icing.· FAA-H-8083-32 — Engine Lubrication Systems
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What type of filter is used to protect the oil pressure spray jets in a turbine engine lubrication system?
Show the answer and explanation
Answer: In-line thread-type (last-chance) filters.
Why: Oil pressure spray jets are protected by small in-line, thread-type last-chance filters fitted immediately ahead of each jet. These catch any debris that would otherwise block the fine spray orifice and are positioned in the line feeding the individual jets.· FAA-H-8083-32 — Engine Lubrication Systems
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A chip detector in a turbine engine oil system is a
Show the answer and explanation
Answer: magnetic plug installed in the scavenge (return) line.
Why: A chip detector is a magnetic plug fitted in the scavenge (return) line, where it attracts and collects ferrous wear particles from the returning oil. Inspecting the captured debris helps reveal impending bearing or gear failure.· FAA-H-8083-32 — Engine Lubrication Systems
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When operating, a gerotor-type oil pump moves oil by
Show the answer and explanation
Answer: carrying it through the changing volumes formed by the intermeshing rotors to the outlet.
Why: In a gerotor-type pump an inner rotor meshes with an outer rotor, and as they turn the oil is drawn in, carried through the changing volumes formed by the intermeshing lobes, and delivered to the outlet. The action carries the oil through the meshing elements rather than only around the outside of the casing.· FAA-H-8083-32 — Engine Lubrication Systems
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Engine oil picks up the most heat from which of the following turbine engine components?
Show the answer and explanation
Answer: The turbine bearing.
Why: The turbine bearing sits closest to the hottest section of the engine, so the oil lubricating and cooling it absorbs the most heat. Compressor bearings and rotor couplings run in cooler regions and transfer far less heat to the oil.· FAA-H-8083-32 — Engine Lubrication Systems
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In a turbine engine that uses a fuel-oil heat exchanger, the oil temperature is controlled by a thermostatic valve that regulates the flow of
Show the answer and explanation
Answer: oil through the heat exchanger.
Why: In a fuel-oil heat exchanger, a thermostatic valve controls how much oil passes through the cooler core versus bypassing it. Per FAA-H-8083-32, the fuel flows continuously on its way to the nozzles, so the oil side is modulated to hold the desired oil temperature.· FAA-H-8083-32 — Engine Lubrication Systems
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What is the purpose of the last-chance oil filters in a turbine engine lubrication system?
Show the answer and explanation
Answer: To prevent clogging of the oil spray nozzles.
Why: Per FAA-H-8083-32, a last-chance filter is a final fine screen fitted just upstream of each oil spray nozzle. It catches any particles that escaped earlier filters so the small spray orifice cannot become blocked, preventing loss of bearing lubrication.· FAA-H-8083-32 — Engine Lubrication Systems
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Which of the following is a function of the fuel-oil heat exchanger on a turbojet engine?
Show the answer and explanation
Answer: Increases fuel temperature.
Why: Per FAA-H-8083-32, the fuel-oil heat exchanger transfers heat from the hot engine oil into the fuel, raising fuel temperature while cooling the oil. Warming the fuel also helps prevent ice from forming in the fuel system. It neither aerates the fuel nor emulsifies the oil.· FAA-H-8083-32 — Engine Lubrication Systems
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At cruise RPM, some oil will flow through the relief valve of a gear-type engine oil pump. This is normal because the relief valve is set at a pressure that is
Show the answer and explanation
Answer: lower than the pressure pump capabilities.
Why: Per FAA-H-8083-32, the relief valve is set below the maximum pressure the pump can produce, so at cruise RPM the pump exceeds that setting and a small amount of oil is continuously relieved. This regulates system pressure and prevents over-pressurization.· FAA-H-8083-32 — Engine Lubrication Systems
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After making a welded repair to a pressurized-type turbine engine oil tank, the tank should be pressure-checked to
Show the answer and explanation
Answer: not less than 5 PSI plus the maximum operating pressure of the tank.
Why: Per FAA-H-8083-32, after a welded repair a pressurized oil tank must be proof-tested to verify the repair is leak-free and strong. The standard test value is not less than 5 PSI above the tank's maximum operating pressure, ensuring integrity at worst-case in-service conditions.· FAA-H-8083-32 — Engine Lubrication Systems
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Failure-related ferrous metal particles in turbine engine oil cause an electrical-indicating type magnetic chip detector to indicate their presence by
Show the answer and explanation
Answer: bridging the gap between the detector center (positive) electrode and the ground electrode.
Why: Per FAA-H-8083-32, an electrical-indicating chip detector has a center electrode and a surrounding ground electrode separated by a small gap. Conductive ferrous particles attracted by the magnet bridge this gap, completing the circuit and triggering the cockpit warning.· FAA-H-8083-32 — Engine Lubrication Systems
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What would be the probable result if the oil system pressure relief valve should stick in the open position on a turbine engine?
Show the answer and explanation
Answer: Insufficient lubrication.
Why: Per FAA-H-8083-32, if the pressure relief valve sticks open, oil is continuously diverted back to the inlet side and system oil pressure falls. The reduced pressure cannot deliver adequate oil to the bearings, resulting in insufficient lubrication and possible bearing damage.· FAA-H-8083-32 — Engine Lubrication Systems
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What is the primary purpose of the oil-to-fuel heat exchanger on a turbine engine?
Show the answer and explanation
Answer: Cool the oil.
Why: Per FAA-H-8083-32, the primary purpose of the oil-to-fuel heat exchanger is to cool the engine oil by transferring its heat into the comparatively cool fuel. Warming the fuel is a useful secondary effect that helps prevent fuel icing, but oil cooling is the main function.· FAA-H-8083-32 — Engine Lubrication Systems
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What type of oil system is usually found on turbine engines?
Show the answer and explanation
Answer: Dry sump, pressure, and spray.
Why: Per FAA-H-8083-32, turbine engines typically use a dry-sump system in which oil is stored in a separate tank, combined with a pressure feed to the bearings and oil delivered as a spray through fine jets. Dip and splash methods cannot reliably lubricate the high-speed bearings of a gas turbine.· FAA-H-8083-32 — Engine Lubrication Systems
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The type of oil pumps most commonly used on turbine engines are classified as
Show the answer and explanation
Answer: positive displacement.
Why: Per FAA-H-8083-32, turbine engine oil pumps are positive-displacement types, such as gear or gerotor pumps, which deliver a fixed volume of oil per revolution regardless of outlet pressure. This guarantees a steady oil supply proportional to engine speed.· FAA-H-8083-32 — Engine Lubrication Systems
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What will result if an engine oil filter becomes completely blocked?
Show the answer and explanation
Answer: Oil will flow at the normal rate through the system.
Why: Per FAA-H-8083-32, a blocked oil filter causes the bypass (relief) valve to open, allowing oil to flow around the filter and continue to the engine at the normal rate. The oil is then unfiltered, but lubrication is maintained to prevent bearing failure.· FAA-H-8083-32 — Engine Lubrication Systems
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A turbine engine dry-sump lubrication system of the self-contained, high-pressure design
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Answer: consists of pressure, breather, and scavenge subsystems.
Why: Per FAA-H-8083-32, a self-contained high-pressure dry-sump system comprises three subsystems: pressure, which feeds oil to the bearings; scavenge, which returns it from the bearing chambers; and breather, which controls chamber pressure. Oil is held in a separate tank, not in a crankcase.· FAA-H-8083-32 — Engine Lubrication Systems
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What is the primary purpose of the hopper located in the oil supply tank of some dry-sump engine installations?
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Answer: To reduce the time required to warm the oil to operating temperature.
Why: Per FAA-H-8083-32, the hopper isolates a smaller volume of oil within the tank so only that quantity must be warmed initially. This reduces the time taken for the oil to reach operating temperature after a cold start, improving warm-up performance.· FAA-H-8083-32 — Engine Lubrication Systems
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What determines the minimum particle size that will be excluded by a Cuno-type (stacked-disc, edge-filtration) oil filter?
Show the answer and explanation
Answer: The spacer thickness.
Why: Per FAA-H-8083-32, in a Cuno stacked-disc edge-filtration filter the cleaning blades pass through gaps set by spacers between the discs. The thickness of those spacers fixes the clearance and therefore the minimum particle size that can pass, so spacer thickness determines the filtration fineness.· FAA-H-8083-32 — Engine Lubrication Systems
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A full-flow oil system has
Show the answer and explanation
Answer: a variable oil pressure dependent upon throttle setting.
Why: Per FAA-H-8083-32, in a full-flow system the positive-displacement pump delivers oil at a rate set by engine speed, so the oil pressure rises and falls with throttle (RPM) setting rather than being held at a single fixed value or switched between hot and cold limits.· FAA-H-8083-32 — Engine Lubrication Systems
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A felt-type oil filter element in a turbine engine lubrication system should be
Show the answer and explanation
Answer: removed and replaced with a new filter element.
Why: A felt filter element traps contaminants within its fibrous body and cannot be satisfactorily cleaned, because solvents leave a residue and degrade the felt. Per FAA-H-8083-32, this type of element is a throwaway item and must be removed and replaced with a new element at the specified interval.· FAA-H-8083-32 — Engine Lubrication Systems
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What type of filter is generally fitted on the inlet side of a turbine engine oil scavenge pump?
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Answer: A wire-mesh screen filter.
Why: A coarse wire-mesh (screen) filter is fitted on the inlet side of a scavenge pump to catch larger debris before the oil enters the pump, protecting it without unduly restricting the high flow of aerated scavenge oil. FAA-H-8083-32 describes these inlet screens in the scavenge subsystem.· FAA-H-8083-32 — Engine Lubrication Systems
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The output of a vane-type oil pump is controlled by
Show the answer and explanation
Answer: outlet pressure acting against spring pressure.
Why: A vane-type oil pump regulates its delivery by balancing outlet (delivery) pressure against a control spring, which adjusts the eccentricity or relief path so that delivery pressure is held within limits as engine speed varies. FAA-H-8083-32 describes pressure-regulated positive-displacement oil pumps.· FAA-H-8083-32 — Engine Lubrication Systems
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In a dry-sump turbine engine oil system, the sump
Show the answer and explanation
Answer: is used as a collecting point only.
Why: In a dry-sump system the sump serves only as a collecting point for oil draining from the bearing chambers, from where the scavenge pumps return it to a separate oil tank. Per FAA-H-8083-32, the bulk of the oil is stored in the external tank, not in the sump.· FAA-H-8083-32 — Engine Lubrication Systems
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A turbine engine gearbox breather is prevented from losing oil to the atmosphere by the action of
Show the answer and explanation
Answer: an impeller and centrifugal force.
Why: A centrifugal breather uses a rotating impeller to fling oil droplets outward by centrifugal force, separating them from the breather air. Per FAA-H-8083-32, the de-oiled air is vented to atmosphere while the separated oil is returned to the system, preventing oil loss through the breather.· FAA-H-8083-32 — Engine Lubrication Systems
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An air-cooled oil cooler is fitted with an anti-surge (bypass) valve in order to
Show the answer and explanation
Answer: protect the cooler core from over-pressure damage.
Why: The anti-surge valve opens to bypass oil around the cooler core when a pressure surge occurs, such as with cold, thick oil at start-up. Per FAA-H-8083-32, this protects the cooler core from over-pressure damage; it does not set general engine oil pressure.· FAA-H-8083-32 — Engine Lubrication Systems
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A thread-type (screw-type) oil seal in a lubrication system
Show the answer and explanation
Answer: has a thread on a stationary portion that pumps oil back toward the bearing.
Why: A thread (screw) type oil seal has a fine thread cut into a stationary member surrounding the rotating shaft. As the shaft turns, the thread pumps any escaping oil back toward the bearing, preventing leakage along the shaft. FAA-H-8083-32 describes such dynamic shaft seals.· FAA-H-8083-32 — Engine Lubrication Systems
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The oil system generally used on most modern turboprop engines is the
Show the answer and explanation
Answer: dry-sump type.
Why: Most modern turboprop engines use a dry-sump oil system, storing oil in a separate tank with engine-driven pressure and scavenge pumps. Per FAA-H-8083-32, this suits their high-speed bearings and varying attitudes far better than a wet-sump arrangement.· FAA-H-8083-32 — Engine Lubrication Systems
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Compared with other positive-displacement designs, a spur-gear oil pump generally produces
Show the answer and explanation
Answer: a low flow rate at high pressure.
Why: A spur-gear pump is a positive-displacement pump that moves a relatively small, fixed volume per revolution but can develop high delivery pressure. Per FAA-H-8083-32, this makes it well suited as the engine pressure-supply pump in a lubrication system.· FAA-H-8083-32 — Engine Lubrication Systems

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Frequently asked questions

What does engine oil do besides lubricate?: It cools, by carrying heat from pistons, bearings, and cylinder walls to the sump, tank, or oil cooler. It cleans, by picking up carbon and metal particles and delivering them to the filter or screen. It seals the gap between piston rings and cylinder walls, cushions shock loads on gears and bearings, and leaves a film that protects internal surfaces from corrosion when the engine sits.
Where is the oil stored in a dry-sump engine?: In a separate oil tank mounted outside the engine, not in the crankcase. A pressure pump draws from that tank and feeds the engine, and one or more scavenge pumps pull oil out of the sump and return it to the tank. The tank includes expansion space above the oil for foaming and thermal expansion, so it is never filled to the very top.
Why is the scavenge pump larger than the pressure pump?: Because the oil coming back is not the same oil that went out. After being thrown around by the crankshaft, gears, and bearings, it is hot and full of entrained air, so the same weight of oil occupies noticeably more volume. Extra scavenge capacity keeps that frothy return moving out of the sump instead of accumulating where it would be churned further.
What does the oil cooler bypass valve do?: It routes oil around the cooler core instead of through it. When the oil is cold and thick at start-up, or when the core is congealed or obstructed, sending oil through the cooler would slow warm-up and could burst the core. The valve senses that condition and opens a path around the cooler, then closes it as the oil reaches normal operating temperature.
What causes high oil temperature during cruise?: Treat it as a symptom rather than an answer. Common causes are low oil quantity, so less oil absorbs the same heat, restricted cooling airflow or a blocked cooler core, a bypass valve stuck open, the wrong oil grade, or an internal problem such as a failing bearing adding friction. Check quantity and the cooling path first, then look inside.

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