A few days ago I was chugging up the M5 around 80mph when one of the main tensioner pulleys failed.... I say main as there are two belts. One that drives the Alternator, Power Steering and Water pump. And another that drives the A/C.

I'd noticed a squeal upon starting the car that was worse in cold damp weather and to be fair it had been doing this since last winter, so didn't come as a great surprise, but of course I didn't know exactly which tensioner it was.

The result of this failure is that you loose alternator, power steering and very importantly, the water pump. As soon as I saw the battery light and the heavy steering I immediately pulled onto the hard shoulder and shut off. Even in the few seconds it took me to cross the lanes the stationery coolant in the engine had boiled and coolant shot out of the pressure relief valve of the header tank.

The twin tensioner part was £75 plus fitting came to £140 in all which wasn't too bad in terms of repair bills.