ASE A1 Engine RepairEngine Block AssemblyMedium
A technician observes unusually high oil consumption and blue smoke from the exhaust, especially during engine deceleration. A compression test shows low readings across all cylinders. Which of the following is the MOST likely cause?
- AWorn or broken piston rings.
- BLeaking head gasket.
- CClogged PCV valve.
- DWorn valve guides or valve stem seals.
Show answer & explanationAnswer & explanation
Correct answer: A. Worn or broken piston rings.
High oil consumption with blue smoke and low compression across all cylinders, especially during deceleration (when high manifold vacuum pulls oil past rings), strongly indicates worn or broken piston rings.
Why the other options are wrong
- B. A leaking head gasket would likely affect only one or two adjacent cylinders and could cause coolant loss or overheating, but less likely systemic low compression and blue smoke.
- C. A clogged PCV valve can cause oil consumption and leaks, but generally not low compression across all cylinders.
- D. Worn valve guides/seals typically cause blue smoke, especially on startup or deceleration, but would not cause low compression across all cylinders.
Piston Ring Failure Symptoms
Worn or broken piston rings cause high oil consumption (blue smoke) and low compression, often worsened during deceleration.
- Reduces cylinder sealing efficiency.
- Allows oil to enter combustion chamber.
- Leads to power loss and increased emissions.
Memory trick: Blue smoke and low compression? Ring failure's the main contention!