Auxiliary belt tensioner replacement

Gradual failure of the auxiliary belt tensioner on the Mk3 petrol is fairly common, causing a tinny rattle to the engine, particularly at idle. It also causes superfluous vibration of the belt, which must accelerate wear of the components it drives: the water pump, A/C compressor, alternator and power steering pump.

If you think your tensioner is on the way out, listen carefully with the bonnet open, the engine cover removed and the engine running at idle. The aux belt is on the left hand side as you stand at the front of the car looking at the engine. Obviously, keep clothing and hair out of the way of the running belt! The alternator can be seen at the back of this side at the top - the tensioner is at the bottom of the engine directly below it. The Haynes manual is sadly quiet on replacement, so here's a quick guide.

Replacement is fairly easy despite the location, but the part isn't cheap. You may also want to replace the belt at the same time - the normal service interval is 150k miles or 10 years, so if you're close to this, do it. You need to partially remove the belt anyway, so replacement is little extra work, just extra cost.

Parts needed