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

New tensioner (FINIS 1371224, 1S7Q-6A228-A*)
New belt if you choose to do this (FINIS 1120198, 1S7Q-6C301-A*)

Tools needed

Wheelbrace & alloy wheel key if required
Jack
Axle stand (optional, but recommended)
8, 10 and 15mm sockets
Torque wrench to do the job properly

Method

It's best to clean up as much as possible prior to starting work. Give the car a good wash, including the wheels and wheelarches.

Accessing the part

Loosen the wheelnuts on the RH front roadwheel.
Jack up the RH front of the car. Pay attention to the jacking points.
Support the car on an axle stand at an appropriate point. You'll be pulling the car around - the standard jack isn't intended for this level of work.
Remove the wheelnuts and the wheel.
Remove the one 8mm and two 10mm headed screws from the lower front plastic cover - circled in green below.

That should give you access to the tensioner, arrowed in green. When working, take care to avoid damaging the crankshaft position sensor (arrowed in red) and the brake line (partially obscuring the tensioner pulley).