FAA Aviation Mechanic Powerplant (AMP)Reciprocating EnginesMedium
During an engine ground run, a technician observes oil pressure that remains abnormally high at all RPM settings, even though oil temperature is within the normal operating range. Which malfunction is most likely responsible?
- AThe oil temperature bulb is malfunctioning
- BThe oil pressure relief valve is stuck closed
- CThe oil pump drive gear is excessively worn
- DThe oil pressure relief valve is stuck open
Show answer & explanationAnswer & explanation
Correct answer: B. The oil pressure relief valve is stuck closed
The oil pressure relief valve limits maximum system pressure by diverting excess oil back to the pump inlet or sump. If it sticks closed (fails to open when pressure exceeds the set value), pressure will build and remain abnormally high regardless of RPM or oil temperature.
Why the other options are wrong
- A. A faulty temperature bulb affects temperature indication, not pressure readings.
- C. A worn pump gear reduces oil delivery, causing low pressure, not high pressure.
- D. A relief valve stuck open would cause low, not high, oil pressure by continuously bypassing oil.
Oil Pressure Relief Valve
A spring-loaded valve in the lubrication system that limits maximum oil pressure by bypassing excess oil back to the pump inlet or sump.
- Set to open at a maximum pressure limit
- Stuck closed causes excessively high pressure
- Stuck open causes low pressure
Memory trick: Closed valve traps pressure like a clogged drain—pressure climbs.