What causes the hissing sound when a car engine is first started?

[DelMakayla]

The reasons for the hissing sound when a car engine is first started: 1. If the car has not been used for a long time, the engine oil will return to the oil pan. When the vehicle starts, the valves will lack the sealing and lubrication of the oil, resulting in a hissing sound, which is normal; 2. The abnormal sound from the belt during startup. In this case, it is necessary to promptly check whether the belt has a problem. An engine is a machine that can convert other forms of energy into mechanical energy, including internal combustion engines, external combustion engines, jet engines, electric motors, etc. For example, an internal combustion engine usually converts chemical energy into mechanical energy. The engine can refer to both the power generation device and the entire machine including the power device.

[McRichard]

My car had a similar issue last time - a hissing sound right after startup, like air leaking or belt friction. Based on my experience, this is mostly caused by belt problems. Think about it: those rubber belts in the engine compartment harden and age over time, with small cracks possibly appearing on the surface, making them prone to slipping and producing this screeching sound during startup. Some vehicle models may experience this when the alternator belt or AC compressor belt becomes loose. Of course, it could also be something more troublesome like water pump bearing wear or compressor failure causing abnormal noises. For safety, I recommend checking the belt condition as soon as possible to see if there are cracks or looseness. If you can't handle it yourself, it's best to take it to a professional repair shop - they can precisely locate the issue using a stethoscope. After all, a broken belt is dangerous as it can suddenly cause loss of power steering.

[DiJayla]

My neighbor Lao Wang's car had this issue before - it made a worrying hissing sound when starting up. He later told me the problem was with the intake manifold gasket. When that rubber seal aged and couldn't maintain proper sealing, the engine would suck in air upon starting, creating that leaking sound. Another common scenario is when the exhaust manifold gasket cracks from aging - exhaust leaks will produce a similar hissing noise. The most troublesome case is turbocharger failure, though that's relatively rare. If the sound resembles metal grinding, it might be the belt tensioner pulley bearing running dry without lubrication. I recommend checking all pipe connections under the hood when the engine's cold, looking for oil stains or carbon deposits. If the sound comes and goes intermittently, pay extra attention - letting a minor issue develop into major damage would be a real shame.

[SanBeau]

The strange noise during startup is indeed worrying. My car had this issue last year. I specifically consulted a mechanic, and he said the first step is to identify the source of the sound. If it's coming from the front of the engine, it's likely an issue with the drive belt or accessory pulley system. When the belt ages, its friction coefficient decreases, causing it to slip and make strange noises during startup as it struggles to drive all the accessories. However, if the sound comes from beneath the engine, it might be an abnormal current sound from the solenoid on the starter motor. A simple way to check is to have someone listen outside the car during startup—if the noise is near the front wheels, it's probably a belt issue, while sounds closer to the bottom of the cabin might indicate a starter motor problem. Don’t judge based solely on the noise level; some minor faults may sound quiet but cause significant damage to the car.

[BlakelyMarie]

After driving for so many years, I've found that the most common cause of cold start noises is belt system failure. Those belts in the engine compartment endure high temperatures, and the rubber material tends to harden and become brittle after three or four years. Especially during cold winter mornings, the belts lose elasticity at low temperatures and can slip momentarily, producing a screeching sound. A stuck tensioner pulley can also exacerbate this noise. Another case I handled for my cousin involved a noise that turned out to be a faulty electromagnetic clutch in the air conditioning compressor. During startup, the compressor failed to engage properly, causing internal parts to rub and create noise. So, besides checking the belts, don’t forget to see if the AC knob position affects the compressor's startup state. Always be cautious when inspecting to avoid getting hit by moving fan blades.