Signs of a Failing Drive Belt Tensioner

If you open the hood of your car and take a look at the engine, you will see one or more rubber belts that wind their way around several gadgets that are hanging off of your engine’s front or side. These belts are called drive belts.

While older cars can have more than one drive belt, most modern cars use a single belt, also known as a serpentine belt (for the way in which it “snakes” itself around all of the necessary components). Drive belts use the rotating power of the engine to “drive” several accessories. These accessories usually include your water pump, alternator, power steering pump, and air conditioning compressor.

As long as your drive belt is under the right amount of tension, all of these accessories should operate correctly and your car should run just fine. Let’s take a look at what your drive belt tensioner is and what it does, signs that it has gone bad, and how to fix it!

What is a drive belt tensioner?

The purpose of your drive belt tensioner is to apply the correct amount of tension to your drive belt. This helps to keep the drive belt in place, preventing it from slipping or coming off (from not enough tension), and also preventing premature wear to the accessories that it drives (from too much tension).

There are several types of drive belt tensioners:

Manual pivot tensioner: This is simply a slotted bracket that attaches the alternator or other engine-driven accessory to the engine. By moving the alternator along the slot, and then tightening the bolt that holds it on, the proper tension can be applied to your drive belt. The good news is that there is nothing to wear out. The not-so-good news is that the tension may have to be periodically readjusted as the drive belt stretches and wears throughout its lifespan.

Spring tensioner: This is a spring-loaded pulley that your drive belt runs through. The pressure of the spring applies the correct amount of tension to your drive belt, even when it stretches over time. Spring tensioners can wear out or seize up and stop applying the correct pressure to your drive belt.

Hydraulic tensioner: This one uses hydraulic oil under pressure and functions like a shock absorber, applying the necessary tension to your drive belt. Hydraulic tensioners can eventually leak, losing both their oil and their ability to tension your drive belt as they should.

Signs of a bad drive belt tensioner

When your drive belt tensioner is failing (or needs adjustment if you have a manual tensioner), there can be a variety of possible warning signs. These include:

• A squealing noise coming from the drive belt at low engine RPMs
• Your drive belt comes off the pulleys
• Your battery warning light comes on
• The drive belt wobbles or tracks off-center
• Rattles or squeaks coming from the spring or hydraulic tensioner
• Rust, corrosion, or cracks on the spring tensioner
• Oil leaking from the hydraulic tensioner
• Your drive belt is worn or damaged (look for fraying, cracks, broken grooves)
• The drive belt’s tension feels loose, allowing you to push it down more than an inch (check only when engine is off)

How do you fix it?

If you have a manual belt tensioner, this is an easy fix. Simply use a wrench to adjust the tension to the proper level. If the drive belt shows any wear, it should be replaced.

If you have a bad spring or hydraulic drive belt tensioner, it is not repairable. It will need to be replaced with a new one. Also replace the drive belt at the same time. Why? Because that worn drive belt is sure to fail soon and leave you stranded. A new tensioner and drive belt, properly installed, will take you many miles down the road.

If you have some experience working on engines, this is not a difficult do-it-yourself project. But because it is not very complicated, it won’t cost much more to have your mechanic do it. The mechanic will also be sure that the belt is properly tensioned after the repair, and will check that all of the engine pulleys that the belt runs through are properly aligned. This will assure you of maximum belt life in the future.