How to Diagnose and Fix Bad Idler Pulleys, Bad Tensioner Pulleys, and More
If you hear a chirping or screeching sound from your car, it could have a bad idler pulley, bad tensioner pulley, bad water pump pulley, or another type of bad pulley. These steps explain how to inspect a bad pulley in your car and what you can do to fix it yourself.
How to Tell If You Have a Bad Pulley
Signs and Symptoms of a Bad Idler Pulley
Different vehicles will have different kinds of pulleys and designs, but there are commonalities. For example, it’s common to have an alternator pulley, idler pulley, tensioner pulley, and water pump pulley, and any of these can go bad. The diagnosis for these pulleys is similar and these symptoms and fixes generally apply, whether you have a bad idler pulley or a bad AC compressor pulley.
1. Chattering, Squealing, or Chirping Sound
If you hear a chattering, chirping, or squealing noise in the car, it’s likely from a bad belt or from a seized or loose bearing in the pulley.
- A chattering noise means there is a seized up or loose pulley
- A squealing noise is from a pulley bearing seizing up and overheating
2. Corroded Surface
- A bad pulley will be rusted and rotted, which can cause premature wear on the serpentine belt.
- A normal pulley in good condition will have a smooth surface.
How to Fix a Rusted Idler Pulley
You can clean off the pulley with sandpaper until it’s clean or replace the pulley.
2. Excessively Loose Idler Pulley
- The loose pulley can make chattering noises as it spins and the vibration can knock the serpentine belt off. A loose pulley can also mean its bearings are bad. If the pulley is excessively loose and there is a lot of play after wiggling it back and forth, it needs to be replaced.
- A normal pulley in good condition will only move slightly.
3. A Bad Idler Pulley May Spin Excessively
- Spin the pulley. If the pulley keeps spinning or spins for more than a few rotations, there is an issue with the bearing. It may also make a noise at normal RPMs.
- A normal working pulley should spin for a few rotations and stop.
4. Slow to No Spin or Binding
- The pulley may also not spin and it may bind up. The center area should remain stable and still while the outer portion spins. If the pulley is binding, it also needs to be replaced, and if the bad pulley is on a part like the alternator or water pump, it will require a rebuild or replacing the part.
- A working pulley should spin for a few revolutions with no resistance and then stop.
How to Test the Pulley with a Pry Bar
A last-resort test to diagnose a bad pulley
- Start the Vehicle
Start the engine and make sure it is running for this test
- Wear Eye and Hand Protection
Wear eye and hand protection before trying this test
- Get a Long Pry Bar
Get a long pry bar or screwdriver
- Place the Pry Bar Near the Pulley
Get as close to the pulley as possible without touching it where the bearing will be.
- Listen for Screeching
Listen for a loud screeching noise, which will indicate the pulley is no good
Replace Bad Idler Pulleys, Bad Tensioner Pulleys, and More Yourself
Replace broken and worn tensioners, bad idler pulleys and more yourself with 1A Auto’s how-to videos that will show you the steps for removing and replacing a pulley on many vehicles.