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Q: What Are Common Signs That Your Drive Belt Is Loose?

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What are common signs that your drive belt is loose?

A: A loose drive belt will often be noisy, squ...

A loose drive belt will often be noisy, squeaking a bit, or emitting a high-pitched squeal. The most obvious sign of a loose drive belt, though, is in its appearance and tension. A loose belt, simply stated, looks and feels loose. If this appears to be the case, you should have a mechanic adjust the belt tension so that it doesn’t come off and damage your engine or leave you stranded.

There are two types of drive belts used in automotive vehicles. They are the v-belt and serpentine belt. Belts are used to rotate components on the engine assembly, such as a coolant pump (water pump). This pump flows coolant through the engine to remove heat.

An alternator produces electricity to maintain a balance on the electrical system and keep the battery charged. If equipped with a power steering pump, it provides assistance in steering the vehicle.

A cooling fan can also be belt driven; this moves air across a radiator to cool the engine coolant to prevent overheating of the engine at slow road speeds or idle. These belt driven components can affect the tension of a belt.

The v-belt type has a narrow taper to a V shape that goes around a pulley. It will have a manual adjustment for the proper belt tension and proper tension will increase its belt life. If the tension is loose, the belt will make a high pitch noise. If you visually look at the belt as the engine is running, there will be a lot of movement with the belt.

Depending on the component the belt is rotating, it will have a low output effect. It will create higher steering effort in the power steering because the power steering pump pulley will have a slipping condition. You will lose frictional contact between pulley and belt, and the pump cannot produce enough pressure. The coolant pump could cause an engine overheating condition. The alternator would cause a low-voltage battery issue, no crank condition, or low system operating voltage. In most of these cases, a Check Engine Light could illuminate.

These components have a bearing to support the pulley. The bearing can fail creating a loose condition at the pulley, making the belt loose. Bearing failure would create a growling type noise (low tone sound).

A serpentine belt is the most common automotive belt type used today. It has a ribbed-wide band design look to it. This belt has an automatic tensioner assembly that maintains the proper tension on the belt under all load conditions. The belt tensioner reacts to a load such as, the A/C compressor operating. Sometimes the belt will make noise when the high load is present only. Automatic belt tensioners operate in a range, they use a calibrated spring to create this tension on the belt, that spring can fail causing a loose belt.

Let's summarize the signs of your drive belt being loose:

  • Sound is an indication of a belt being loose. This noise could manifest as a high pitch or whirring noise. The level of looseness will create different sounds.

  • Movement of the belt up and down while operating is normal at ½” to ¾”. More than that is considered worn or a concern

  • Low output from the component the belt is operating could be an indication of a loose belt

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