ASE G1 Auto Maintenance and Light RepairEngine SystemsHard
A vehicle's engine develops a noticeable ticking or tapping sound that seems to come from the top of the engine, especially prominent during cold starts and sometimes becoming quieter as the engine warms up. This noise does not typically change with engine RPM as dramatically as a rod knock. What is the most likely cause?
- AAn exhaust manifold leak
- BA worn crankshaft bearing
- CA collapsed hydraulic lifter
- DA failing main bearing
Show answer & explanationAnswer & explanation
Correct answer: C. A collapsed hydraulic lifter
A ticking or tapping sound from the top of the engine, especially on cold starts and potentially quieting when warm, is characteristic of a collapsed or worn hydraulic lifter. These components rely on oil pressure to maintain proper valve lash, and low oil pressure or worn components can cause noise until oil flow stabilizes.
Why the other options are wrong
- A. An exhaust manifold leak can produce a ticking or 'chuffing' sound, but it's typically more consistent and less likely to quiet down significantly with engine warmth as a lifter would.
- B. A worn crankshaft bearing would produce a deep 'thump' or 'knock' from the bottom of the engine, usually proportional to RPM, not a ticking from the top.
- D. A failing main bearing would produce a heavy, deep knock from the bottom of the engine, distinct from a top-end ticking.
Hydraulic Lifter Noise
A collapsed or worn hydraulic lifter (tappet) causes a distinct ticking or tapping sound from the top of the engine, often more noticeable on cold starts due to insufficient oil pressure or worn components.
- Noise comes from the top of the engine.
- Often worse when cold, improves as oil pressure builds.
- Indicates insufficient oil to lifter or lifter wear.
- Affects valve lash and can reduce engine efficiency.
Memory trick: Top tick, cold start, lifter's playing a noisy part.