How to inspect serpentine belts for wear causing squealing noise.

Learn How to Diagnose and Fix Belt Squeal on Startup

Engine belts like the serpentine belt or the timing belt help time and operate different parts of the engine and hearing belt noise like a screech or squeal on startup, especially when it’s cold outside, probably means an engine belt needs replacing. These steps explain how to diagnose an engine belt and what might happen if one is worn.

How to Diagnose Serpentine Belt Noise

Symptoms of a Bad Engine Belt

Cracked belt
Loose belt
Belt squeal or serpentine belt noise on startup
Belt squeal when turning the vehicle

If you hear a loud squealing or squeaking noise when starting the vehicle, especially in the cold, you might have a worn engine belt. Hearing a squeaking noise when turning might also mean the engine belt is worn.

Causes of a Serpentine Engine Belt

A belt on a manual tensioner will slip as it wears, making a squealing serpentine belt noise. A belt on an automatic tensioner will not squeal because the tensioner picks up the slack. Engine belts can also stretch and crack from use.

How to Check For Serpentine Belt for Wear

How to Inspect an Engine Belt

Check for Tightness
Feel how tight the belt is. The belt should not feel stretched, loose, or overly flexible on the pulleys, and should not feel stiff or hard off the pulleys
Check for Wear
Wear can make a belt squeal. Since the belt has grooves, it might look smooth with worn rubber marks or less rubber, like a tire after a burnout
Look for Cracks
Look for cracks, brittling, or dry rotting in the rubber
Look for Broken Grooves
Look for broken, missing pieces, or a loss of grooves since they can deteriorate and break apart over time
Check for Fraying
Check the edges of the belt for fraying or splitting

How to Replace Engine Belts

Some engine belts can be replaced by novices. Some parts may need to be removed to access the belts and in some cases the engine cover. Replacing a timing belt, for example, will require more time and expertise than a serpentine belt.

Check out 1A Auto’s how-to video library to learn how to replace different kinds of engine belts on your vehicle. Our video library has instructional videos for many different makes and models.