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▷▷ 2021 ▷ Symptoms of a bad or failing idler pulley

3 julio, 2021

For Dan collins

Published December 10, 2018

The engine of our cars is not only responsible for producing the energy necessary to turn the wheels. It also generates the energy necessary to run other components in our vehicles so that we have a more comfortable, safe and definitely more pleasant trip. But what if the system that connects these components to the engine breaks down or starts to fail?

car engine

The idler pulley

We said that the engine is the power source of our car, literally. In the engine there are drive belts that are connected to various components such as the air conditioning compressor, the power steering pump, the alternator and the water pump. Each of these components requires energy to function and must extract this energy from the power produced by the motor.

Since the energy produced by the engine comes from the linear movement (generally up and down) of the pistons, this must be transmitted to the crankshaft to convert it into rotary movement. The drive belts that are connected to the engine also move as the crankshaft rotates. As these drive belts work, they also power the various components that depend on the power of the engine, such as the power steering pump, the water pump, the air conditioning compressor, and the alternator. Without the engine drive belts, there will be no mechanism to transmit the rotary motion of the engine crankshaft to the power needed by these components.

Engine drive belts follow a specific path in a very specific way designed by the car manufacturer to optimize the energy transmitted to the various components or accessories. These drive belts must be guided and positioned in such a way that they do not interfere with each other or with other nearby components in the engine compartment. This is the function of the accessory belt pulleys.

Cars have 2 types of belt pulleys, the idler pulley and the tensioner. Some cars have only one of each type, although there are those that may have more than one idler pulley. Idler and idler pulleys look the same and work the same way, too. They eliminate the often annoying engine drive belt vibration that usually occurs if there is too much slack in the drive belt system. The difference between the two is that the idler pulley is mounted on a fixed frame while the idler pulley is attached to an adjustable device.

Specifically, the idler pulley provides a smooth and efficient pivot point for the car’s engine belt drive to move and twist, avoiding unnecessary play. This also helps increase the tension on the belt, allowing the engine to deliver power to the different accessories in a more efficient way. The idler pulley also acts to prevent slippage of the flat belt drive. As the name implies, a flat belt is one that has a relatively flat surface throughout the length of the belt. The pulley prevents this belt from slipping out of position. The idler pulley may have a smooth outer wall, but the edges often have retainers, while some may have a middle groove to hold the drive belt in place.

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How to tell if you have a bad or failing idler pulley

We know that an idler pulley rotates on its own axis, moving the motor drive belt along its path. As such, a bad or failing idler pulley can lead to the following symptoms.


How many of us always worry about inspecting the engine drive belt system every time we take our cars out of our garages? The chances are very slim. While we do check our brake fluid levels, transmission fluid levels, and radiator fluid levels, very few of us will see the integrity of our drive belts, let alone the pulley. As such, the only time we can be alerted to the presence of a bad or even failing idler pulley is when we start the engine and hear that deafening screech coming from under the hood. Screaming is one of the first signals to alert us to a problem, although the problem may have existed long before.

Remembering what we said about the idler pulley ensuring the proper path for the drive belt, a squeal is almost always indicative that an idler pulley bearings are really bad. The bearings allow a smoother rotation of the …

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