Automotive Service Excellence (ASE) A8 Engine PerformanceGeneral Engine DiagnosisMedium
A vehicle exhibits excessive oil consumption (1 quart per 1,000 miles) but shows no external oil leaks. The exhaust has a bluish tint, especially during acceleration after idling. What is the most likely cause?
- AA clogged PCV valve.
- BWorn valve stem seals.
- CA faulty turbocharger.
- DA leaking oil cooler.
Show answer & explanationAnswer & explanation
Correct answer: B. Worn valve stem seals.
Bluish exhaust smoke, particularly after idling and during acceleration, is a classic symptom of oil burning due to worn valve stem seals. During idle, oil can seep past the seals, and then it burns off when the engine accelerates.
Why the other options are wrong
- A. A clogged PCV valve can lead to oil leaks or sludge buildup, but is less likely to cause consistent blue smoke on acceleration after idle compared to worn valve seals.
- C. A faulty turbocharger (specifically internal seal failure) can cause blue smoke, but it's typically more constant and often accompanied by a distinct whine or loss of power.
- D. A leaking oil cooler would cause an external oil leak, not oil consumption through combustion.
Oil Consumption Diagnosis - Blue Smoke
Identifying the cause of engine oil burning, characterized by bluish exhaust smoke, to differentiate between internal engine wear and external leaks.
- Blue smoke indicates oil burning.
- Smoke on acceleration after idle points to valve stem seals.
- Constant blue smoke suggests piston rings or turbo issues.
Memory trick: Blue smoke's a clue, 'cause oil's burning through.