ASE A1 Engine RepairLubrication and Cooling SystemsMedium
A vehicle's cooling system is losing coolant, but no external leaks are visible, and the engine oil appears normal. The exhaust has a distinct sweet smell and produces white smoke, especially on cold starts. A combustion leak detector test shows positive. What is the most likely cause?
- AA failed radiator cap
- BA cracked engine block
- CA leaking intake manifold gasket
- DA blown head gasket
Show answer & explanationAnswer & explanation
Correct answer: D. A blown head gasket
Coolant loss with no external leaks, normal oil, sweet-smelling white exhaust smoke, and a positive combustion leak test are classic indicators of a blown head gasket. This allows combustion gases to enter the cooling system and coolant to enter the combustion chamber.
Why the other options are wrong
- A. A failed radiator cap would cause coolant loss and possibly overheating, but not typically sweet-smelling white exhaust smoke or a positive combustion leak test.
- B. A cracked engine block is possible, but a blown head gasket is a much more common failure mode for these specific combined symptoms.
- C. A leaking intake manifold gasket could cause coolant loss and possibly white smoke on some engines, but a positive combustion leak test points more directly to a head gasket or block issue.
Blown Head Gasket Symptoms
A blown head gasket allows combustion gases and coolant to mix, leading to unexplained coolant loss, sweet-smelling white exhaust smoke, and often a positive combustion leak test.
- Unexplained coolant loss (no external leaks)
- Sweet-smelling white exhaust smoke
- Positive combustion leak test
- Engine overheating (common)
Memory trick: Sweet smoke, no oil mix? Head gasket's the fix!