Rick's Free Auto Repair Advice

When to replace a serpentine belt

When should I replace my serpentine belt

Do you know when to replace a serpentine belt? Do you replace it as soon as you see cracks? If so, how many cracks? Well, you’ve come to the right place because I’m going to ‘splain it all to you.

Serpentine belts are made from either Neoprene or ethylene propylene diene terpolymer (EPDM). Nitrile belts generally last about 30,000 to 40,000 miles before cracking to the point where they need replacement. How many cracks before you replace a serpentine belt?

Replace a neoprene serpentine belt when it has three or more cracks in a 3-inch section.

when to replace a serpentine belt, crack in serpentine belt.

This one is toast. It has too many cracks in a a three inch section.

replace serpentine belt

This one must go–too many cracks in a three-inch section

Replace a Neoprene serpentine belt when chunks are missing

replace serpentine belt

Replace if any ribs are missing

But EPDM serpentine belts are different

EPDM doesn’t crack like neoprene. They last much longer–almost 100K miles. But they’re also much harder to evaluate. In fact, the mini ribs can wear to the point where the small “V” ribs no longer wedge into the tapered pulley grooves. When that happens, the pulley engages with the top ridge of the belt. The tensioner can apply more tension, but since the belt has far less surface area engaged with the pulley grooves, it slips. Simply put, an EPDM belt can look fine, but if the ribs are worn, the belt will slip.

Illustration showing how to determine if serpentine belt is worn

This illustration shows how rib wear can cause the belt to lose gripping power. The belt’s only contact with the pulley is at the bottom of the rib valley. It simply loses its ability to wedge into the pulley “V”. So the belt slips, chirps, squeals and the driven component loses efficiency.

So you can’t judge EPDM belt wear with just a visual examination. You must use a gauge to actually

You need a wear gauge to measure how deep the ribs have worn. Gates offers a free app for apple and android devices. You boot up the app and snap a picture of the belt ribs. The app measures the wear.

serpentine belt wear app

Click here to see how the Gates serpentine belt wear app works

Check the backside of the serpentine belt

And don’t forget to check the backside of the belt. The backside of a serpentine belt drives the water pump and idler pulleys. It can glaze over, chunk out, fray, or simply wear too thin.

© 2015, Rick Muscoplat

serpentine belt wear

Backside wear

serpentine belt wear

Notice the wear on the backside. This can cause squealing and slipping


©, 2015 Rick Muscoplat



Posted on by Rick Muscoplat

Custom Wordpress Website created by Wizzy Wig Web Design, Minneapolis MN