What Causes the Abnormal Noise After a Cold Start?
3 Answers
Abnormal noise after a cold start can be caused by poor oil lubrication or carbon canister solenoid valve noise. The specific reasons are as follows: Poor oil lubrication: When a car is parked for a day, the engine oil basically all flows back to the oil pan. During a cold start, the oil pump cannot immediately establish oil pressure, and oil film formation between components is delayed. Especially for the valves inside the cylinder head, they lack lubrication during a cold start. Whether it's hydraulic lifters or mechanical rocker arms, there will be some valve clearance, resulting in abnormal noise. Carbon canister solenoid valve noise: The function of the carbon canister solenoid valve is to open the electromagnetic valve between the carbon canister and the intake manifold after the engine starts. This not only reduces emissions but also lowers fuel consumption. However, noise may occur during its operation.
I've been repairing cars for over 20 years, and cold start noises are extremely common. Belts can squeak when they get wet or age, just like rubber bands hardening over time. Insufficient lubrication inside the engine can also cause metal friction sounds, especially in northern winters when temperatures drop below zero and oil flows slower, leaving valve lifters prone to dry friction. The exhaust system can also act up, with the catalytic converter making particularly loud cracking noises as it contracts in the cold. The key is to observe the frequency of the noise: if it's a continuous tapping or metal knocking sound, it's likely due to insufficient oil pressure in the hydraulic lifters; a brief squeak is usually just belt slippage. I recommend warming up the car for a minute to let the oil circulate and see if the noise persists. If it continues, immediately check the belt tensioner and oil viscosity.
Last year, my car had the same issue—annoying rattling noises from the chassis during cold starts. I initially thought the engine was failing, but it turned out to be just the thermal expansion and contraction at the exhaust pipe connections. Actually, identifying strange noises depends on their location: a high-pitched squealing from the front is likely a slipping belt, a clattering sound near the transmission could indicate a flywheel problem, and clicking from the exhaust pipe is just normal metal expansion. The most deceptive is the carbon canister purge valve, which makes a knocking-like "tick-tick" sound when operating. Since then, I’ve developed a habit: during every service, I ask the mechanic to thoroughly inspect the belt for cracks and the bearing system, and I switch to 0W oil in cold weather. If a new strange noise suddenly appears, I immediately head to the repair shop to pinpoint it with a stethoscope—unlike my neighbor who stubbornly drove until the belt snapped.
