From a cold start-up, just put your seatbelt on and drive. No need to worry about it. A diesel will take forever to warm up if you just leave it idling, so drive away.

When switching off, the only time you really need to let the motor idle is if you've been cruising at high speed for a while, and (for example) pull into a service station quickly ... in other words, if you go from 80+mph to a dead stop in 30 seconds. In these situations, just let the motor idle for a minute. It helps dissipate the heat from the turbo.

In most other circumstances, after a fast drive you'll be driving at low speed through urban areas / towns, which also dissipates heat, so here it's not necessary to wait the minute before switching off.

Is it worth idling for 30s or so on start-up to let oil circulate around the turbo bearings?

The turbo kicks in at such low revs in a modern turbodiesel that it's not really possible to drive 'off-boost' for the first mile or so...

Surely at a steady 80 mph on the Motorway,the turbo wouldn't be boosting ?

If so, one would never get decent mpg ?

The turbo is only there to force extra fuel into the engine when one needs more performance,at least that's what I believed !

The turbo is only there to force extra fuel into the engine when one needs more performance,at least that's what I believed !

No. Turbos force more air into the engine. In a diesel, this always improves thermal efficiency.

In petrols, air flow is directly coupled to fuel flow and petrols usually perform poorly on boost.

At a steady 80 mph, a typical 2 litre diesel will be producing a modest amount of boost -probably 5 psi or so. This still provides a useful leaning effect. VG turbos can start producing boost at less than 20% of rated output.

Well I've learnt something there ! I've been wrong for years !

Never too old too learn eh ?

Regards - Mick.

Thanks to all for your valuable tips and advice.

As a first time diesel car user, I really needed this.

Its only over the past few years here in Australia, diesel engined cars have become popular.

After a daily 15 km run each way in heavy traffic, which takes me a minumum of 45 min and upto 70 min to do this daily trip to work (which will give you an idea of how bad the traffic is here in Sydney) I ensure that the engine remains on for about a minute before I turn it off. After a steady 30 min run at about 80-90 km per hr on the motorway, I keep the engine running for 90 to 120 seconds before turning off.

At start, I just leave it on for about 30 seconds, which I may discontinue based on advice received. I will just take off.

cheers