Turbo heat

[SGH1]

I was told by a friend that after a spirited drive in my BiTdi, I should let the car idle for a few minutes before switching off as the turbos get too hot. I'm not mechanically minded, and would have thought the car would protect itself from damage caused by this. I want to treat my car with appropriate mechanical sympathy, so my questions to the forum are: is this legitimate advice, does the car not have systems to protect against this, and what is actually happening if this is a risk?

[zollaf]

about the best advice you will ever get. a turbo does indeed get hot, very hot. it is driven by hot exhaust gas after all. a petrol turbo can and will glow cherry red if pushed hard. turn it off with a hot turbo and the oil supply stops. oil is used to cool it and some are also water cooled. the oil left in the turbo will then burn and form carbonised deposits. too much of this and the oil way blocks with it thus leading to oil starvation and a new turbo being required. allowing the car to cool down on tickover for a while will let the turbo cool so removes the problem. some high performance cars are fitted with turbo timers so you tun the engine off and it stays running for a minute.

[SGH1]

Thanks zollaf, how long would you typically wait?

[zollaf]

it depends on what you have done. i have a 3 or 4 mile drive along slow country lanes before my house, so i just pootle along those and turn the engine straight off, as that driving doesn't use the turbo. if you have been doing 130 mph along an autobahn and pull into the services, then i would be giving it about 2-3 minutes. after 'general' driving, 20 -30 seconds should suffice. this can be the difference between a turbo that lasts 40,000 miles and one that lasts 250,000 miles.

[Doctle Odd]

People don't do it any more Z IMO it contributes to many of the turbo problems in modern cars

[daycartes]

about the best advice you will ever get. a turbo does indeed get hot, very hot. it is driven by hot exhaust gas after all. a petrol turbo can and will glow cherry red if pushed hard. turn it off with a hot turbo and the oil supply stops. oil is used to cool it and some are also water cooled. the oil left in the turbo will then burn and form carbonised deposits. too much of this and the oil way blocks with it thus leading to oil starvation and a new turbo being required. allowing the car to cool down on tickover for a while will let the turbo cool so removes the problem. some high performance cars are fitted with turbo timers so you tun the engine off and it stays running for a minute.

An excellent explanation Zollaf, thanks.

[skibuddy]

Does this apply to any turbo diesel or just the biTDI?

[zollaf]

any turbo'd engine, petrol, diesel, one turbo or 2 (or 3,4 etc..).

[Mike'A]

Could this advice apply to petrol turbos as well? Do they differ from one fitted to a diesel engine? These days there is no or little information regarding this in many manuals, suggesting there is no need for such actions, it was common practice to leave the engine ticking over to enable the turbo to slow down whilst still getting an oil supply to those hard worked bearings, is this no longer the case? Has turbo design changed? I too like zollaf slow things down before switching the engine off. I'm intrigued as to why information in manuals appears not to cover this in any detail, any ideas?

[zollaf]

petrols more so really, as they tend to run hotter than oil burners.
if you told everyone they couldn't just turn their engine off, how many would follow the advice ? people would run a mile. most turbo's don't tend to get run hot and hard enough anyway so most turbo's will make it out of warranty. many years ago only 'real ' drivers had a turbo, nigel mansell, ayrton senna and those that could afford something like a cossy or audi s2. now all cars have a turbo, near enough. maybe this is why so many turbos seem to self destruct so early and give turbo's an unreliable name. they are still the same design as 30 years ago, not much has changed. i swapped my 305 mile turbo for one that had 180k on it, as the original high mile one had a bit of play. the low mile one is as new. treat a turbo badly enough and destroy it within a few runs. treat it well and it will last a lifetime. these new vn't require running hard when they are hot to prevent clogging, but still need running down.