FAA Aviation Mechanic Powerplant (AMP)Fuel, Induction and LubricationHard
During overhaul, a mechanic inspects an oil cooler's thermostatic bypass valve. Which statement correctly describes its function when the engine oil is cold?
- AThe valve opens the bypass passage, routing oil directly to the engine and away from the cooler
- BThe valve remains fully closed at all times regardless of oil temperature
- CThe valve diverts oil to the fuel heater to warm the fuel supply
- DThe valve closes the bypass passage, forcing all oil through the cooler to reach operating temperature faster
Show answer & explanationAnswer & explanation
Correct answer: A. The valve opens the bypass passage, routing oil directly to the engine and away from the cooler
When oil is cold and thick, the thermostatic bypass valve opens the bypass passage so oil flows directly to the engine bearings, bypassing the cooler, allowing the oil to reach normal operating temperature quickly and preventing excessive pressure drop through a cold, restrictive cooler core.
Why the other options are wrong
- B. The valve is thermostatically actuated and does change position with temperature.
- C. Oil coolers are not connected to fuel heating systems.
- D. Forcing cold, thick oil through the cooler would cause excessive pressure drop and slow warm-up, opposite of actual function.
Oil Cooler Thermostatic Bypass Valve
A temperature-sensitive valve that routes oil around the cooler when cold to speed warm-up and through the cooler when hot to control operating temperature.
- Opens bypass when oil is cold, sending oil directly to engine
- Closes bypass and routes oil through cooler core when oil is hot
- Protects against excessive pressure drop through a cold cooler core
Memory trick: Cold oil takes the shortcut; hot oil takes the scenic cooler route.