Any ideas on if & how long should we be idling the engine & cooling the turbos down before switch off? I've spoken with BMW & they have no position on it. I know TD engines run cooler the petrol so do we need to idle the motor at all ?????

 

I think that my local BMW person would probably say.. 'what diesel?'

 

It's not for cooling the engine, but to cool off the turbo. 30 - 60 seconds would be enough.

The turbo is greased with the engine oil. When the engine is hot (after a long ride, or after heavy duty) and you turn-off the engine right away, the oil isn't being pumped through the turbo anymore. Because of the heat, the existing oil around the turbo will evaporate and therefore the turbo won't be lubricated anymore (because the turbo spins so many rpm, it doesn't stop right away).

Hope I explained it right. If not, hopefully someone will correct me!

 

I don't hink you have to nowadays, i haven't seen anything in the handbook, and having run diesels for the last few years i have not had any problems just turning them off.

 

I don't usually leave the engine running to cool the turbo, although I've been told it's more important to let it idle when you've just been driving it hard (a mate of mine who has had several 330d's always let them idle for 30-60 seconds before switching off if he'd just had a fast run).

 

It's indeed only when you had a fast run, or for example when you're stopping for gas at the Autobahn.

The 35i engine has special watercoolers for the turbo's, so this is the only engine where the cooling off period is not needed.

 

I think that advances in turbo bearing technology, cooling and lubrication systems and fluids, have reduced or even eliminated the cool-down recommended in past years. That said, I always make it a habit (regardless of what car I'm driving) to take the last few minutes at a more relaxed pace to permit a 'gentle' shut down at the end of a journey.

This might parallel the same advice about the start up ... drive the first few minutes at a moderate pace to get systems up to temp before beating your car to death!

 

EGT have to cool down before shutdown... even in the 35d...

just let it rattle for about 1 min 30 sec if you have been reving it before coming home....

i've made a good rule not to rev it while driving in the streets around home...

just ease off the pedal, for the last 2 minutes you drive home, idle for 15sec.. and kill it...

 

You could be right, but what is the factual information that leads to what you believe? To clarify a couple posts' assertions above, the turbos are both lubricated and cooled by engine oil, and with high EGTs the problem with an immediate shutdown has been coking of the stationary engine oil within the turbocharger's channels. This coking then leads to reduced oil circulation and on an ongoing basis has historically caused premature turbo failures.

Maybe this scenario has been eliminated through some combination of design and oil chemistry, I don't know. But if it were me, given that I keep my vehicles several years and the possible $ consequences of turbo failure, I think I'd let the turbo cool down a little before switching off. Petrol or diesel, it would be my practice until I was shown factually that it isn't necessary. Others may chose to do differently,

Cal

 

thanks for your feedback - my opinion is to let it rattle for a few minutes to, certainly won't harm it & like others here this is a keeper so might as well do what you can make it last......ta