FAA Aviation Mechanic Powerplant (AMP)Fuel, Induction and LubricationHard
A pilot reports that during a long descent, the engine oil temperature dropped significantly, causing a noticeable increase in engine friction and reduced oil pressure. What component is likely malfunctioning?
- AThe oil pressure relief valve.
- BThe oil filter bypass valve.
- CThe oil cooler thermostatic bypass valve.
- DThe engine-driven oil pump.
Show answer & explanationAnswer & explanation
Correct answer: C. The oil cooler thermostatic bypass valve.
If the oil cooler thermostatic bypass valve is stuck open or malfunctioning, oil will continuously flow through the oil cooler, even when temperatures are low (like during a long descent). This overcooling can lead to excessively low oil temperatures, increased viscosity (friction), and reduced oil pressure.
Why the other options are wrong
- A. An oil pressure relief valve stuck open would cause low oil pressure but not necessarily excessively low oil temperature.
- B. An oil filter bypass valve stuck open would allow unfiltered oil to circulate but wouldn't directly cause overcooling.
- D. An engine-driven oil pump malfunction would typically cause a general loss of oil pressure or no oil pressure, not specifically overcooling.
Oil Cooler Thermostatic Bypass Valve
A valve that regulates the flow of engine oil through the oil cooler, bypassing it when oil is cold and directing it through the cooler when hot, maintaining optimal oil temperature.
- Maintains oil at operating temperature.
- Stuck open leads to overcooling.
- Stuck closed leads to overheating.
Memory trick: Thermo valve stuck open, oil gets too cold, like shivering.