The Volkswagen (VW) belt tensioner pulley tightens the serpentine belt that turns the engine accessories, such as the air-conditioning compressor and water pump. The newer model VWs have an automatic tensioner pulley that tightens the serpentine belt as it stretches, but the older model VWs have a tensioner pulley that needs to be adjusted. The tensioner pulley shows symptoms when it is going out or requiring replacement.
Serpentine Belt Squealing
The VW belt tensioner pulley can become too tight or too weak, allowing the serpentine belt to wear prematurely or slip under normal operating conditions. The belt begins to squeal when the tensioner pulley is not tight enough, causing the engine to overheat because the water pump is not operating efficiently. This symptom can be caused by the tensioner pulley spring, which weakens over time and does not place enough tension on the belt. The serpentine belt can also begin to run too hot and prematurely fail. The tensioner pulley needs to be replaced when these symptoms occur.
The engine in the VW can overheat when there is a problem with the belt tensioner pulley. This symptom is caused by corrosion building up on the tensioner pulley that does not allow the pulley to adjust the serpentine belt. When corrosion builds up, the pulley becomes jammed or does not rotate, causing the serpentine belt to stretch and loosen on the engine accessories. The corrosion does not allowing the pulley to adjust to the stretched belt, creating the water pump problem. This corrosion is generally caused by road debris and dampness splashing onto the tensioner pulley. Proper lubrication of the tensioner pulley periodically can prevent this corrosion build-up.
Another symptom of a VW belt tensioner pulley going bad is the battery not charging properly. A failing tensioner pulley does not provide enough tension on the serpentine belt, preventing the alternator from recharging the battery. The loose serpentine belt does not allow the alternator to turn fast enough to charge the battery, and the battery can quit working or fail to provide enough charge to the ignition and electrical system to start the engine. The tensioner pulley needs to be replaced or inspected when the serpentine belt is replaced to ensure that the tensioner pulley keeps operating efficiently.