Why does the engine squeak when cold but not when hot?
2 Answers
Cold engine squeaking while hot engine remains quiet is mainly caused by poor sealing of engine valves, inadequate lubrication; overly tight belts or bearing noise. If abnormal noises persist after the engine warms up, it is recommended that the owner promptly visit a repair shop for inspection to identify the specific cause. When a car is parked for more than a day, the engine's lubricating oil basically all flows back to the oil pan. During a cold start, the oil pump cannot immediately establish oil pressure or form an oil film between components, especially in the cylinder head and internal valves, which do not receive lubrication during a cold start. Whether it's hydraulic lifters or mechanical rocker arms, there will be some valve clearance, leading to a tapping noise. After the engine runs for a while, oil pressure is established, the oil film forms, and the oil temperature rises. Once the engine operates normally, the tapping sound disappears, which is a normal condition.
A typical symptom is a squeaking sound from the engine when cold but not when hot, often caused by belt aging or tensioner failure. Cooling contraction makes the belt hard and prone to slipping and squeaking; thermal expansion restores normal tension. The water pump bearing may also produce friction noise during cold starts due to insufficient lubrication. Checking for belt cracks and tension is crucial. Ignoring this can lead to more expensive issues, so early intervention ensures smooth driving.
