What Causes the Zizzing Sound After a Cold Start?
3 Answers
Reasons for abnormal sounds after a cold start include poor oil lubrication and noise from the carbon canister solenoid valve. The details are as follows: Poor Oil Lubrication: After a car has been parked for a day, the engine oil mostly flows back into the oil pan. During a cold start, the oil pump cannot immediately build up oil pressure to form an oil film between components. Especially the valves inside the cylinder head do not get lubricated during a cold start, leading to a certain valve clearance whether it's hydraulic lifters or mechanical rocker arms, which results in abnormal noise. Carbon Canister Solenoid Valve Noise: The carbon canister solenoid valve opens 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 can occur during its operation.
I remember when I drove my old car, on winter mornings when starting the engine, I often heard a squealing sound that seemed like something was rubbing. That was actually a belt issue, especially the alternator belt or AC belt. When cold, the rubber hardens and becomes slightly loose, making it prone to slipping and producing noise. Later when I opened up my car, I saw cracks on the belt with severe wear. Upon starting, it would rub against the metal edge of the pulley, creating that high-pitched sound. Another time it was the water pump bearing - insufficient lubrication when cold caused the bearing to rotate slowly, producing similar noise. If not repaired promptly, the belt might snap, leading to charging system failure or AC breakdown. Back then, I immediately replaced the belt and checked the tensioner to ensure proper tightness. During regular maintenance, remember to have the mechanic inspect belt conditions to avoid sudden failures affecting your trips. While the sound is annoying, it's not a major issue and can be easily resolved if addressed early.
I've repaired quite a few cars, and the squealing sound is common during cold starts. The main cause is usually a fault in the belt system, such as aging or slipping of the alternator belt or fan belt. When the engine is cold, it contracts, reducing the belt tension, and the hardened rubber creates noise as it rubs against the pulley. During inspection, first use a stethoscope to locate the sound—if it's coming from the front of the engine, it's likely a belt issue. Then press the belt to check if it's loose. Additionally, it could be due to bearing wear, such as in the alternator or water pump, where poor lubrication during cold starts can also cause squealing. It's best to listen for a few seconds after startup; if the noise persists, parts need replacement. My experience is not to delay—if the belt cracks, not only is the noise annoying, but it might also snap and affect the car's performance. Regular maintenance can prevent this. If you're a beginner and can't handle it yourself, it's better to take it to a workshop for inspection—it's more convenient and worry-free.
