What causes the thud sound when starting the car after it has been parked for several days?
2 Answers
This occurs due to ignition delay, where unburned gasoline is expelled into the exhaust pipe just as the spark plug ignites, causing the atomized gasoline to combust within the exhaust system and produce the sound. The primary cause is prolonged parking, which drains the battery and leads to this abnormal noise. Precautions for long-term vehicle storage are as follows: 1. Disconnect the battery's negative terminal: Even when the vehicle is locked with the remote, the anti-theft system remains active. Although the voltage is low, extended periods can still deplete the battery, preventing the car from starting next time. 2. Protect the paintwork: Use a car cover to shield the vehicle. This prevents rapid oxidation of the paint due to exposure to sun and rain, and also avoids excessive interior temperatures from direct sunlight. 3. Check tire pressure: Ensure the tire pressure is adequate. If it's too low, inflate to the standard pressure to prevent insufficient pressure after long-term parking, which could hinder driving upon next startup.
Once I left my car parked outdoors for several days, and when I started it again, I heard a clunking sound. This is usually due to rust on the brake discs because prolonged parking in humid conditions causes rust to form on the discs, making a noise when the brakes are released. It typically goes away after driving a few meters. It could also be due to rusted suspension ball joints or bushings sticking, which release and make a popping sound when starting. It's advisable not to leave the car parked for too long after rain, regularly lubricate chassis components, or lightly press the brakes a few times before driving to warm them up and prevent rust, ensuring the brake system operates smoothly. If this happens frequently, it might indicate aging components, so timely inspection is recommended to prevent potential hazards.
