22 Engine Lubrication Systems Practice Questions & Answers

1. 1. Besides reducing friction between moving parts, engine oil in a reciprocating engine performs which additional set of functions?

   • A.Cooling, sealing the piston rings against the cylinder wall, cleaning by carrying particles to the filter, cushioning shock loads, and corrosion protection✓ Answer
   • B.Cooling, sealing the crankcase breather, cleaning by burning off deposits in the cylinders, cushioning valve seating, and preventing detonation
   • C.Cooling, sealing the valve stems in their guides, dissolving carbon deposits already formed, cushioning shock loads, and corrosion protection
   • D.Cooling, sealing the piston rings, chemically neutralizing acids in the crankcase, damping crankshaft torsional vibration, and raising fuel octane

   Oil does five jobs beyond reducing friction: it carries heat away from bearings and piston undersides, it completes the gas seal between the rings and the cylinder wall, it cleans by holding particles in suspension until the filter traps them, it cushions the shock loads imposed on crankshaft and rod bearings by combustion, and its residual film prevents corrosion on parked engines. Oil is a dispersant carrier, not a solvent, so it cannot dissolve deposits already formed, and it has no effect on fuel octane or detonation.

   Source: FAA Aviation Maintenance Technician Handbook — Powerplant, Lubrication and Cooling Systems (functions of engine oil)Report a problem with this question

2. 2. Which factor has the greatest effect on the viscosity of an engine oil in service?

   • A.The temperature of the oil, because viscosity falls sharply as the oil is heated✓ Answer
   • B.The quantity of oil in the sump, because a full sump recirculates its charge less often
   • C.The oil pressure in the system, because pressure compacts the oil molecules
   • D.The engine speed in rpm, because the pump shears the oil more rapidly at high rpm

   Viscosity is resistance to flow, and it is dominated by temperature: heating an oil thins it and cooling thickens it, which is why oil pressure reads high on a cold engine and why a grade is chosen for the climate and the operating temperature the engine sees. Pump shear, system pressure, and sump quantity do not change the oil's viscosity in any comparable way.

   Source: FAA Aviation Maintenance Technician Handbook — Powerplant, Lubrication and Cooling Systems (viscosity and temperature)Report a problem with this question

3. 3. What does a high viscosity index tell a mechanic about an oil?

   • A.Its viscosity changes comparatively little over a wide range of operating temperatures✓ Answer
   • B.It has been refined to a higher quality level than another oil of the same viscosity grade
   • C.Its viscosity is high enough to protect the bearings under the heaviest crankshaft loads
   • D.It thickens rapidly when heated, which keeps the oil film intact on hot cylinder walls

   Viscosity index expresses the rate at which viscosity changes as temperature changes, so a high index means a small change over a wide temperature range: the oil is still thin enough to circulate on a cold start and still thick enough to hold a film when hot. It is not a measure of quality, and no oil thickens when heated.

   Source: FAA Aviation Maintenance Technician Handbook — Powerplant, Lubrication and Cooling Systems (viscosity index)Report a problem with this question

4. 4. A container of aviation oil is marked W100. What does the letter W indicate?

   • A.The oil is a straight mineral oil with a pour point depressant added to it
   • B.The oil is a synthetic oil approved for turbine and piston engines alike
   • C.The oil is a winter-weight oil intended for cold-weather starting below freezing
   • D.The oil is an ashless dispersant oil with a viscosity comparable to commercial grade 100✓ Answer

   In aviation oil designations a W placed in front of the grade number identifies an ashless dispersant oil, and the number that follows is the commercial viscosity grade. This is routinely confused with the automotive SAE system, where a W after the number (20W) means a winter rating; the two conventions are unrelated.

   Source: FAA Aviation Maintenance Technician Handbook — Powerplant, Lubrication and Cooling Systems (oil classification and ashless dispersant designation)Report a problem with this question

5. 5. A newly overhauled horizontally opposed engine is being returned to service. Which lubrication practice is correct?

   • A.Break the engine in on straight mineral oil, then change to ashless dispersant oil once oil consumption has stabilized✓ Answer
   • B.Break the engine in on a blend of mineral and ashless dispersant oil, then drain and refill with synthetic turbine oil
   • C.Break the engine in on the preservative oil left in from assembly and leave it in service until the first annual inspection
   • D.Break the engine in on ashless dispersant oil, because its additives seat the rings faster and hold wear metal in suspension

   New, newly overhauled, and freshly recylindered reciprocating engines are broken in on straight mineral oil because an ashless dispersant oil can retard ring and cylinder wall seating and produce high oil consumption. When consumption stabilizes the oil is drained, not mixed, and dispersant oil is used thereafter, with the first change made early and the filter examined for sludge. Turbocharged engines are the exception, being broken in and operated on dispersant oil, and turbine synthetic oil is never used in a piston engine.

   Source: FAA Aviation Maintenance Technician Handbook — Powerplant, Lubrication and Cooling Systems (break-in with straight mineral oil; changing to ashless dispersant oil)Report a problem with this question

6. 6. How does a dry sump lubrication system differ from a wet sump system?

   • A.The oil is delivered to the bearings as a mist by the crankcase breather instead of by a pressure pump
   • B.The oil is stored in the accessory case and returns to the bearings by gravity with no pump at all
   • C.The oil supply is carried in a separate tank, and scavenge pumps return the oil from the engine to that tank✓ Answer
   • D.The oil supply is carried in the crankcase, and a scavenge pump shifts it between the front and rear sumps

   A wet sump engine keeps its oil supply in the crankcase sump; a dry sump engine keeps it in an external tank, and scavenge pumps plus external plumbing return the oil that collects in the engine to that tank. Radial and turbine engines use dry sump systems because their oil collects in several places, because a large external supply is needed for cooling, and because a wet sump floods the engine in inverted flight. All aircraft engines are pressure lubricated, or pressure and splash; splash alone is never used.

   Source: FAA Aviation Maintenance Technician Handbook — Powerplant, Lubrication and Cooling Systems (wet sump and dry sump systems)Report a problem with this question

7. 7. Why is the capacity of the scavenge pump greater than the capacity of the pressure pump in a dry sump system?

   • A.Scavenged oil is foamy and mixed with air, so it occupies more volume than the oil the pressure pump delivers✓ Answer
   • B.The scavenge pump runs at a lower drive speed than the pressure pump and must displace more per turn
   • C.Scavenged oil is cooler and therefore denser, so a larger pump is needed to move the same weight of oil
   • D.The scavenge pump must also supply oil to the propeller governor and to the turbocharger controller

   Oil returning from the bearings has been churned by rotating parts and is full of entrained air, so the same weight of oil now occupies a much larger volume. The scavenge elements must therefore have greater capacity than the pressure element, or oil would accumulate in the engine faster than it could be returned to the tank. Scavenged oil is hotter, not cooler, than the oil leaving the tank.

   Source: FAA Aviation Maintenance Technician Handbook — Powerplant, Lubrication and Cooling Systems (scavenge pump capacity)Report a problem with this question

8. 8. As bearing clearances increase with normal wear, what happens in the lubrication system at a given rpm?

   • A.Pump output stays about the same, and less oil is returned to the pump inlet through the relief valve✓ Answer
   • B.Pump output drops off sharply because the gears cannot keep up with the enlarged bearing clearances
   • C.Pump output stays about the same, and more oil returns to the pump inlet through the relief valve
   • D.Pump output rises automatically because the relief valve senses the loss and commands more flow

   The engine driven oil pump is positive displacement, so at a given rpm it delivers essentially the same volume regardless of engine condition. Wider bearing clearances simply let more of that fixed output pass through the engine, so the relief valve returns less oil to the pump inlet to hold the set pressure. The pump cannot sense wear or increase its own output.

   Source: FAA Aviation Maintenance Technician Handbook — Powerplant, Lubrication and Cooling Systems (oil pump and pressure relief valve operation)Report a problem with this question

9. 9. Where is the oil pressure relief valve located, and what does it do?

   • A.Between the filter and the tank return line, sending the unfiltered oil back there when it clogs
   • B.Between the pump and the engine's internal system, bypassing excess oil back to the pump inlet✓ Answer
   • C.Between the scavenge pump and the cooler, holding pressure on the cooler core to prevent surging
   • D.Between the oil tank and the pump inlet, bleeding the air out of the oil before it reaches the pump

   The valve sits downstream of the pump and upstream of the engine's internal oil passages, and it works as a regulating valve: when pump output exceeds what the system needs, it opens and routes the surplus back to the pump inlet, holding the pressure the engine sees within limits. Because a positive displacement pump would otherwise build pressure without limit as rpm rises, some oil passes through this valve at cruise as a normal condition.

   Source: FAA Aviation Maintenance Technician Handbook — Powerplant, Lubrication and Cooling Systems (oil pressure relief valve)Report a problem with this question

10. 10. A mechanic must adjust engine oil pressure. Which procedure is correct?

    • A.With the engine cold and shut down, turn the adjusting screw counterclockwise to raise the pressure setting
    • B.With the oil at operating temperature and the engine running, turn the adjusting screw clockwise to raise the pressure✓ Answer
    • C.With the engine cold and running, turn the adjusting screw clockwise to lower the indicated pressure
    • D.With the oil at operating temperature and the engine at takeoff power, add washers beneath the spring

    Oil pressure is adjusted with the oil at normal operating temperature and the engine running at the speed the maintenance manual specifies, after confirming that the oil in the engine is the correct grade, because cold or wrong-viscosity oil gives a false reading. Turning the adjusting screw clockwise adds spring tension and raises the pressure; counterclockwise lowers it. The locknut is loosened before and retightened after each adjustment, and the target value comes from the current maintenance data.

    Source: FAA Aviation Maintenance Technician Handbook — Powerplant, Lubrication and Cooling Systems (adjusting oil pressure)Report a problem with this question

11. 11. What happens when the element in a full-flow oil filter becomes completely clogged?

    • A.A bypass valve opens and unfiltered oil continues to be supplied to the engine bearings✓ Answer
    • B.The pump shear section parts to protect the drive and the engine runs on splash lubrication
    • C.A bypass valve opens and the oil is routed back to the tank until the element is changed
    • D.Oil flow to the bearings stops and the low pressure warning switch shuts the engine down

    In a full-flow system all of the oil passes through the filter on its way from the pump to the bearings, so the filter housing contains a bypass valve. When the element clogs, or when cold congealed oil will not pass through it, the differential pressure opens the bypass and unfiltered oil goes on to the bearings, because dirty oil is far less damaging than no oil at all. Finding the bypass open is a reason to investigate the element, not evidence that flow stopped.

    Source: FAA Aviation Maintenance Technician Handbook — Powerplant, Lubrication and Cooling Systems (full-flow filter bypass valve)Report a problem with this question

12. 12. In an oil cooler fitted with a flow control valve, what path does cold oil take?

    • A.Straight into the engine bearings, bypassing both the tank and the pressure relief valve
    • B.Through the core tubes first, so that the temperature element warms quickly and opens the valve
    • C.Back through the scavenge pump for a second pass until the bellows senses operating temperature
    • D.Around the core through the annular bypass jacket and on to the tank without being cooled✓ Answer

    The flow control, or thermostatic, valve on the cooler senses oil temperature and chooses the path. Cold oil is sent around the core through the annular bypass jacket so it is not cooled further and warms up quickly; as the oil heats, the thermostatic element expands, closes the jacket outlet, and forces all of the oil through the core tubes, where cooling air passing through the tubes carries the heat away.

    Source: FAA Aviation Maintenance Technician Handbook — Powerplant, Lubrication and Cooling Systems (oil cooler flow control valve)Report a problem with this question

13. 13. Federal airworthiness regulations require the oil tank of a reciprocating engine installation to have an expansion space of at least what amount?

    • A.Ten percent of the tank capacity or one-half gallon, whichever is less
    • B.Two percent of the tank capacity, the same as a reserve tank not connected to an engine
    • C.Five percent of the tank capacity or one quart, whichever the tank shape will permit
    • D.Ten percent of the tank capacity or one-half gallon, whichever is greater✓ Answer

    14 CFR 25.1013 requires a reciprocating engine oil tank to have an expansion space of not less than the greater of ten percent of tank capacity or one-half gallon, while a turbine engine oil tank needs ten percent of capacity and a reserve tank not directly connected to an engine needs two percent. The rule also requires that it be impossible to fill the expansion space inadvertently while the aircraft is on the ground, since the oil must have room to expand and foam as it heats.

    Source: 14 CFR 25.1013(a) — oil tank expansion spaceReport a problem with this question

14. 14. What is the purpose of the hopper, or temperature accelerating well, built into some oil tanks?

    • A.It holds a reserve of oil for feathering the propeller after the engine is shut down in flight
    • B.It traps water and sediment at the bottom of the tank where they can be drained before flight
    • C.It reduces the volume of oil circulated during warm-up so the oil reaches operating temperature sooner✓ Answer
    • D.It swirls the returning oil against the tank wall so that entrained air separates before the oil is reused

    The hopper is an inner compartment connected to the tank outlet, so only the oil inside it circulates during warm-up. Circulating a smaller quantity lets the oil reach operating temperature much faster on a cold morning, and where oil dilution is installed only the hopper oil has to be diluted. Air separation is the job of the tangential return line and the tank baffles, not of the hopper.

    Source: FAA Aviation Maintenance Technician Handbook — Powerplant, Lubrication and Cooling Systems (hopper tank / temperature accelerating well)Report a problem with this question

15. 15. Why do turbine engines use a synthetic oil of much lower viscosity than a reciprocating engine oil?

    • A.Turbine bearings run cooler than piston engine bearings and would never need a heavy oil film
    • B.Turbine rotors ride on antifriction ball and roller bearings, which need a thin film that flows freely when cold✓ Answer
    • C.Turbine oil is consumed as it passes through the bearings, and a thin oil limits that consumption
    • D.Turbine oil also serves as the hydraulic fluid for the fuel control, which requires a thin fluid

    A turbine rotor is carried on antifriction ball and roller bearings with no reciprocating parts and no large running clearances, so it needs only a thin film, and that oil must still flow at low starting temperatures while resisting coking at high ones. A reciprocating engine needs a much heavier oil because of its large clearances, sliding bearings, and high bearing pressures. Turbine bearings run hotter, not cooler, and turbine oil is not a fuel control hydraulic fluid.

    Source: FAA Aviation Maintenance Technician Handbook — Powerplant, Lubrication and Cooling Systems (turbine engine lubricants)Report a problem with this question

16. 16. What is the purpose of the dwell chamber, or deaerator tray, in a turbine engine oil tank?

    • A.To hold a reserve of oil for restarting the engine after an in-flight shutdown
    • B.To warm the returning oil with bleed air so the pump inlet is not starved on a cold start
    • C.To settle water and sediment out of the returning oil so they can be drained at each servicing
    • D.To separate the air entrained in the scavenged oil before that oil returns to the pressure pump✓ Answer

    Scavenged turbine oil returns to the tank badly aerated. The dwell chamber, or deaerator tray, gives that oil time and surface area for the entrained air to break out and vent through the tank vent, so the pressure pump is fed solid oil rather than foam. Feeding aerated oil to the bearings would give erratic pressure and a poor film at the bearing jets.

    Source: FAA Aviation Maintenance Technician Handbook — Powerplant, Lubrication and Cooling Systems (turbine oil tank deaerator)Report a problem with this question

17. 17. What is the primary purpose of the fuel-oil heat exchanger on a turbine engine?

    • A.To heat the fuel so that ice crystals cannot block the fuel filter, cooling the oil incidentally
    • B.To cool the engine oil, while incidentally warming the fuel enough to prevent filter icing✓ Answer
    • C.To hold the fuel control at a steady temperature so that its metering stays in calibration
    • D.To raise the oil temperature quickly after start so the oil reaches its operating viscosity

    The fuel-oil cooler is an oil cooler that uses fuel on its way to the engine as the cooling medium, so its primary purpose is to cool the oil; warming the fuel enough to keep ice crystals from blocking the fuel filter is a useful by-product. A thermostatic valve lets the oil bypass the cooler when no cooling is needed, and that spring-loaded bypass also opens if the cooler becomes dented or clogged.

    Source: FAA Aviation Maintenance Technician Handbook — Powerplant, Lubrication and Cooling Systems (fuel-oil heat exchanger)Report a problem with this question

18. 18. Where are the last-chance filters in a turbine engine lubrication system, and why do they matter?

    • A.In the tank vent line ahead of the deoiler; they are cleaned at every scheduled oil servicing
    • B.Downstream of the scavenge pumps ahead of the cooler; they are inspected at every filter change
    • C.In the accessory gearbox ahead of the pressure pump; they are removed and washed at each inspection
    • D.At each bearing just ahead of the oil jet; they are reachable only when the engine is disassembled✓ Answer

    Last-chance filters are fine screens installed at each bearing immediately upstream of the fixed-orifice spray nozzle, and their job is to catch any particle that could block that small orifice. They are not accessible for routine cleaning; because they can only be reached with the engine disassembled, a clogged last-chance filter is normally discovered as part of a bearing failure investigation.

    Source: FAA Aviation Maintenance Technician Handbook — Powerplant, Lubrication and Cooling Systems (last-chance filters and oil jets)Report a problem with this question

19. 19. A magnetic chip detector pulled from a turbine engine scavenge line carries a light gray metallic fuzz. What does this indicate, and what should the mechanic do?

    • A.Nonferrous debris shed by the oil cooler; replace the cooler and send an oil sample for analysis
    • B.A shorted detector circuit; replace the detector and disregard the material found on the element
    • C.Normal wear; clean the detector, reinstall it, safety wire it, and return the engine to service✓ Answer
    • D.Bearing failure; the engine must be removed and the whole oil system flushed before any further flight

    A magnetic chip detector attracts ferrous particles only, and a small amount of fine fuzz or gray metallic paste is the product of normal wear. Chips, slivers, or flakes are what call for investigation of the source before further flight. The normal action for fuzz is to clean the detector, reinstall it with a new seal as required, safety wire it, and continue in service.

    Source: FAA Aviation Maintenance Technician Handbook — Powerplant, Lubrication and Cooling Systems (magnetic chip detectors)Report a problem with this question

20. 20. What is the limitation of a spectrometric oil analysis taken from an engine for the first time?

    • A.A first sample reads high in every metal because assembly residue is still suspended in the oil
    • B.A first sample gives no trend of its own, so it cannot forecast the engine's condition reliably✓ Answer
    • C.A first sample measures only nonferrous metals, so iron wear is left entirely unevaluated
    • D.A first sample cannot detect iron or chromium until the engine is past its break-in period

    Spectrometric oil analysis reports wear metals in parts per million, and its value lies entirely in the trend built from successive samples taken at regular intervals. A single first sample establishes a baseline but has nothing to be compared against, so no accurate forecast of engine condition can be made from it; that is why a program should begin when the engine is new and continue for its whole life.

    Source: FAA Aviation Maintenance Technician Handbook — Powerplant, Lubrication and Cooling Systems (spectrometric oil analysis)Report a problem with this question

21. 21. The oil pressure gauge on a reciprocating engine fluctuates widely between zero and normal pressure. What is the most probable cause?

    • A.A partially clogged full-flow filter element holding the bypass valve wide open
    • B.A restricted oil cooler core that sends the oil through the bypass jacket
    • C.A broken or weak relief valve spring that lets the valve chatter on its seat✓ Answer
    • D.An oil grade heavier than the one the maintenance data lists for the season

    A wide, rapid swing from zero to normal is the classic signature of a relief valve that is no longer being held on its seat, most often from a broken or weakened spring, so the valve opens and closes erratically instead of regulating. A clogged filter, a heavy oil grade, or a restricted cooler changes the pressure level or the temperature steadily; none of them produces a fluctuation of that kind.

    Source: FAA Aviation Maintenance Technician Handbook — Powerplant, Lubrication and Cooling Systems (oil pressure troubleshooting)Report a problem with this question

22. 22. A horizontally opposed engine is using an excessive amount of oil, and no external leaks can be found. Which condition is most consistent with the finding?

    • A.Worn valve guides that let oil be drawn down the stems into the cylinders✓ Answer
    • B.A partially clogged oil cooler core that raises the oil temperature in cruise
    • C.A loose oil temperature bulb that indicates below the actual oil temperature
    • D.A relief valve adjusted a few psi above the value the maintenance manual specifies

    When oil is disappearing with no external leakage it is being burned in the cylinders, and worn valve guides are a leading cause: manifold pressure below the guide draws oil down the valve stems into the combustion chamber. High oil consumption is in fact the best single indication of worn guides. Worn rings and, on radial or inverted engines, oil pooling in the lower cylinders are the other internal paths, while relief valve setting, cooler condition, and an indicating fault do not consume oil.

    Source: FAA Aviation Maintenance Technician Handbook — Powerplant, Lubrication and Cooling Systems (excessive oil consumption; worn valve guides)Report a problem with this question

Practice questions based on the Aviation Mechanic Airman Certification Standards (FAA-S-ACS-1), 14 CFR parts 43, 65, and 91, and the FAA Aviation Maintenance Technician Handbook—Powerplant (FAA-H-8083-32). This site is not affiliated with or endorsed by the Federal Aviation Administration. This bank covers the POWERPLANT written test only; the General and Airframe written tests and the oral and practical tests are separate. Torque values, running clearances, compression limits, magneto timing angles, spark plug gaps, temperature and pressure limits, servicing quantities, and overhaul intervals always come from the manufacturer's current maintenance data, the type certificate data sheet, and the applicable airworthiness directives — never from a practice test. Confirm current eligibility and testing requirements with the FAA before you test. About the A&P mechanic certificate →