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[r1]

 a mate has just bought a 1.2 renault clit which is quite a fast car[100 bhp] which has a low pressure turbo.now on my 2.5 diesel i always let my car tick over for a while before switching it off to look after the bearings in the turbo. he has now asked the garage where he bought it from [main dealer] and they said you dont need to do this.it sounds wrong to me but i dont know so any one any thoughts? do low pressure turbos work diffrent?

[aaronjb]

They work in exactly the same way (well, in that there's still a central shaft spinning around in oil - either with plain bearings or ball/roller bearings).. but no dealer is going to tell people that they have to do something special or unusual to look after their shopping trolley

Fully synthetic oil is much more resistant to cooking and coking up the bearings than semi or mineral ever was, but it's still not a bad idea to either not rag it the last couple of miles or sit with it ticking over for a minute or two. Though to be fair, I just used to do the former on the MR2 and the turbo was just peachy after 30k (a plain bearing IHI unit) - given a low pressure unit ought to be less stressed with (one would think) lower EGTs, he'll likely be fine unless he comes barrelling into the car park/garage on boost

[doz]

Modern oils make a lot of difference. Something like my LC which is running 20/50 Semi I let spoil down. If you've been driving normally then your be ok. If you've just been giving it the beans then let it idle for a while. Most people have just pootled in from the commute home in that situation just switch it off. If you've just finished the Le Mans 24 hour Asda car park race then it's probably best to let it idle

[Lazydocker]

I always let any car, turbo or not, warm up gently before giving it the beans and cool down a little at the end of the journey. At least 5 mins either end is normally enough and I normally let it Idle while I sort my sh!t out and get ready to get out, which is normally 30 seconds to a minute

[aaronjb]

I always let any car, turbo or not, warm up gently before giving it the beans and cool down a little at the end of the journey. At least 5 mins either end is normally enough and I normally let it Idle while I sort my sh!t out and get ready to get out, which is normally 30 seconds to a minute

Ditto - never figured out how other people seem to scream to a halt and have the engine off & door open before the car has settled on it's suspension.. I just can't do it that fast!

[Marks DTM Calib]

I personaly wouldn't run an engine for more than 30 seconds on idle before turn off.

[aaronjb]

I personaly wouldn't run an engine for more than 30 seconds on idle before turn off.

You must stop & start a lot in traffic jams, then

[Marks DTM Calib]

I personaly wouldn't run an engine for more than 30 seconds on idle before turn off.

You must stop & start a lot in traffic jams, then

As above....before turn off. (RTFP!) 

There is a an understanding that, particularly on turbos, they will cool a good amount within 30 seconds of idling. Furthermore, whilst idling on modern engines the oil pressure is still pretty high and hence oil can seep past the turbos seals which can sit in the turbo assembly for some time .

[r1]

thanks for all the replies.
now he users to do some home delivery parcel service so lots of stop start says he will try to keep it ticking over but not to bothered as its under warranty!!!

[D]

I had a focus ST with a turbo and it had been mapped by Mountune. The ST forums were full of people suggesting waiting a few mins to let it cool down etc.

Me on the other hand, would start and show it no mercy straight away. Similarly on stopping I couldnt be ars** to let it tick over and would just stop and shut off. Did 50k before I sold it to a colleague at work. He is now on 90k I think and still no issues. You could say I was lucky. On the other hand to remember to let it cool down etc, I really didnt have the time to waste and at the end of the day its only a car. There are more important things to worry about.

If its a clit, then I wouldnt really bother. Perhaps if it was a M5, then I would probably be a bit more careful, maybe....

[maracus]

Don't the focus st have an electric oil pump that keeps pumping after the engines turned off??

[D]

Who knows. I just wanted to beat the sh** out of that engine and enjoy it. Which I did. 

[Kevin Wood]

The fact that a turbo survives the abuse it gets "on boost" without melting despite the turbine and compressor rotors being small in mass tells me that the path for heat to be conducted away from these parts into the oil, coolant, turbo housing or wherever is pretty effective, thus it would only take a few seconds "off boost" for it all to cool off again. Leaving it idling for minutes is probably not going to help.

Yes, the heat from the exhaust side of the turbo casing will soak through into the oil in the bearing, but that isn't going to cool significantly until you stop the engine, so you can't really help that. Just use a decent synthetic oil so the oil in the bearing can cope with the heat. This will be why some turbo cars have an electric oil or coolant pump that "runs on" - to stop the oil / coolant sitting in the turbo after switch off from overheating.