ASE A1 Engine RepairLubrication and Cooling SystemsHard
A technician is performing a cooling system pressure test. The system is pressurized to 15 PSI. After 10 minutes, the pressure has dropped to 10 PSI, and no external leaks are visible. The engine oil appears normal, but the technician notices a strong sweet smell from the exhaust and periodic white smoke, especially on startup. What is the most likely cause of the pressure drop?
- AInternal head gasket leak into the combustion chamber
- BExternal heater core leak
- CCracked engine block
- DFaulty radiator cap
Show answer & explanationAnswer & explanation
Correct answer: A. Internal head gasket leak into the combustion chamber
A pressure drop during a cooling system pressure test with no external leaks, combined with a sweet smell and white smoke from the exhaust (especially on startup), strongly indicates an internal head gasket leak where coolant is entering the combustion chamber and being burned.
Why the other options are wrong
- B. An external heater core leak would result in visible coolant leaking into the cabin or from under the dash, which contradicts 'no external leaks are visible'.
- C. A cracked engine block could cause similar symptoms, but a head gasket leak is a more common failure point for coolant entering the combustion chamber in this scenario without affecting the oil (as oil appears normal).
- D. A faulty radiator cap could cause pressure loss, but it wouldn't typically lead to a sweet smell or white smoke from the exhaust.
Head Gasket Leak (Combustion Side)
A failure of the head gasket allowing coolant to leak directly into the engine's combustion chambers, leading to coolant loss and exhaust symptoms.
- Causes cooling system pressure loss without external leaks.
- Results in white, sweet-smelling exhaust smoke.
- Can lead to engine overheating and misfires.
Memory trick: Pressure drop, no drip, means an internal slip.