What Causes the Squealing Noise in a Newly Replaced Belt?

[LeJade]

Newly replaced belts may produce a squealing noise due to the presence of metal, stones, or other impurities on the friction surface, or because the belt tension is inappropriate. Reasons for Replacement: To ensure the normal operation of the engine and extend its service life, reliable and regular maintenance is essential. For ordinary vehicles, the engine belt should be replaced after one and a half to two years of use. If the mileage reaches 60,000 kilometers, replacement is necessary. Hazards of Belt Breakage: If the belt breaks while driving, it poses a significant safety risk. In such cases, the owner cannot replace the belt themselves and must rely on a repair shop. Considering various factors, replacement is recommended when the total mileage reaches 80,000 kilometers. Solutions for Belt Noise: If the belt makes unusual noises, first check the assembly. The noise may be caused by friction between the timing belt and the timing cover. Loosening the screws on the timing cover by half a turn can help determine if the noise disappears. Additionally, inspect the condition of the generator belt. If the noise comes from the accessory belt, it might be due to the timing belt being adjusted too tightly. Removing the generator and air conditioning power steering belts can help identify if the issue lies with these belts.

[EmersynLynn]

Last time I replaced the alternator belt myself, I also encountered a squealing noise. This kind of sharp noise is 90% likely caused by belt slippage—either the new belt surface is too smooth or it wasn't tensioned properly during installation. Once, a mechanic applied chalk to the inner side of the belt, and the noise stopped immediately—the principle is to increase friction. Remember, never use engine oil as a temporary fix, as it will only make things worse! Here's a lesser-known tip: replacing belts in sub-zero temperatures is especially prone to squealing because the rubber hardens, causing tension changes. If the noise persists after adjusting the tensioner, it's best to remove the belt and check if there's any coolant or power steering fluid contamination in the pulley grooves.

[StAaron]

The newly replaced belt is squealing like a whistle? I've looked into this. Belt tension is crucial—press the middle of the belt with your thumb, a 5-6mm deflection is ideal, anything over 10mm will definitely cause slippage. Some apprentices at repair shops cut corners by not replacing the tensioner pulley bearings, and worn bearings can't properly drive the new belt. Once, my car made noise on rainy days, and the mechanic said it was due to low-quality belts swelling when wet—switching to a brand-name part fixed it. I recommend checking if the crankshaft pulley has developed a mirror-like surface; overly smooth pulleys can't grip the belt properly.

[Kennedy]

New Belt Squealing Focus on Three Areas: First, check if the idler pulley is aligned correctly—even a half-millimeter misalignment can cause the belt to scrape and squeal. Next, verify if the belt model is correct—the rib depth difference between 6PK and 7PK is 1mm, and mixing them will definitely cause noise. Last week, a neighbor’s car squealed after a belt replacement, and it turned out the A/C compressor bearing was failing—the new belt couldn’t handle the old bearing. A reminder: when replacing the belt, it’s best to replace the idler pulley and tensioner as a set. Rubber belts last about 4 years, but metal components may not last that long.

[LondynAnn]

This is a common case in my auto repair shop. Belt squealing resembling a whistle mostly occurs during cold starts and tends to ease as the engine warms up, which is a typical break-in phenomenon for new belts. However, persistent screeching is dangerous: one customer used a non-OEM belt that cracked after just 300 km. Nowadays, high-quality belts incorporate nylon fibers, while inferior products use recycled rubber prone to stretching. There's also a hidden danger—a deformed alternator mounting bracket can cause belt misalignment. I recommend using a stethoscope to pinpoint the pulley with the loudest abnormal noise.