Nanny your turbo
QI have a Saab 9000 with a 2.3-litre turbo engine. I often read advice about letting turbo engines run ‘for a while’ before switching them off. Why is this, and how long is ‘a while’? robert Young, Winchester
AExhaust gases pass through the turbocharger, making it very hot. If the engine is turned off after the turbo’s been worked hard – such as a stretch of highspeed motorway driving or a thrash around a circuit – the engine oil is ‘cooked’ in the turbocharger’s bearings. This lays down abrasive carbon deposits and reduces the life of both the oil and the bearings.
Letting the engine idle for a couple of minutes allows the circulating oil to cool the turbo, so no harm is done. Don’t bother if you’ve been pottering around, but it’s a very good idea if you’ve been driving hard.