Idler pulleys seem to be a fairly unimportant part of your car. However, they play a critical role in maintaining optimum performance for your air conditioning, power steering, alternator, and water pump. They are an inexpensive part and don’t take too long to change out. But when do you need to schedule the maintenance before the pulley fails?

What is an Idler Pulley?

Nearly every car, truck, and SUV on the road today have one or more idler pulleys under the hood. They are usually about two to four inches in diameter and are mounted to the front of the engine block. They roll freely, are not connected to a power source, and do not provide power to any unit. It may appear that they serve no real function, but they are actually a crucial moving part of your vehicle.

Maintaining the Path for Optimum Belt Performance

The idler pulley serves to redirect the path of your serpentine or timing belt for optimum contact between the belt and the crankshaft, water pump, or other auxiliary pulleys. The larger the contact patch for the belt, the more power that is transferred from the crankshaft to the various pumps and motors controlled by the serpentine belt. If an idler pulley goes out of alignment or stops working, it will significantly impact the performance of the vehicle.

Inspect Your Pulleys when Servicing the Serpentine or Timing Belts

Your idler pulleys are designed to last as long as the belt that they support. Most manufacturers recommend inspecting the serpentine belt for wear every 10,000 miles after the 30,000-mile mark. As you tug on the belt to check for cracks, worn edges, and depth of grooves, you should also give the idler pulleys a spin. The belt should ride over the pulley without resistance. You can expect to replace the idler pulley between 50,000 and 100,000 miles.

Indications of a Worn Out Idler Pulley

How do you know if you need to replace the idler pulley? The belt ought to move smoothly over the pulley when you turn the crankshaft. There should be no chips or cracks on the edges of the pulleys. The pulley should spin evenly and not immediately stop or grind. If you see any of these problems, you should plan to replace all the pulleys associated with the serpentine belt.

Another obvious indication of a problem with your pulley is a loud squealing caused by uneven rubbing on the serpentine belt. The squeal may go away after the engine warms up, but returns with each cold start of the engine.

The reason for changing all the pulleys and not just the one with obvious problems is that they all were manufactured at the same time and likely have the same number of miles of wear on them. That means that you can expect all the pulleys to fail similarly within a few thousand miles of one another.

What Happens when an Idler Pulley Fails?

If a pulley seizes up, it will increase friction and wear on the serpentine belt. A rough edge on a pulley can grab at the belt and actually rip off parts of the belt. Once your serpentine belt fails, you can lose your power steering, engine coolant system, and air conditioning. That leads to engine overheating and potentially can cause you to get into an accident.

It is very noticeable if a belt completely fails. You may hear a loud thump under the hood followed by a sudden change in steering.

How Long Does it Take to Replace an Idler Pulley?

Your local repair shop will charge you an hour or two to replace one idler pulley. But if you have the tensioner pulley, serpentine belt, and all idler pulleys changed at the same time, it will likely add just one more hour to labor costs while completely replacing the serpentine belt system.

If you are doing the job at home, give yourself about four hours to change all the parts. You will need the following tools and parts: