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.

[Mike'A]

Thanks, vn't? I've 1.4 tsi does that have one? It's just done 2,400 mls in France in a fortnight and performed brilliantly returning an average of 46 mpg, considering load, speed and town and city work I thought that was a good return.

[zollaf]

most modern stuff has a vnt rather than wastegated. it means you get planty of boost from low down the revs rather than waiting until 2000 rpm and the boost hitting you like a bus driving into the back of your car.

[skibuddy]

So Stop Start is a bad thing then for your turbo?

[zollaf]

if you are in traffic then stop start won't matter. if you come off a motorway into the services and stop then you don't want the engine to stop, so in this situation its bad.

[silo24]

Bear in mind that the synthetic oils used in modern Turbocharged engines are designed to ensure that these issues do not occur and you do not have to let the engine idle before shutdown.

The main issue that used to affect turbo engines was oil residue sitting under no pressure on the hot turbo and cooking off, leaving carbon deposits which then cause friction problems or oil blockages, meaning extra wear.

These new oils are designed to withstand these temperatures hence less of an issue and no "post-running" needed. Having said all the above, it won't do any harm at all just to be sure as those temperatures probably don't do the oil much good, despite it not burning off.

[jbanfie]

There is another thing in your favour here, the Bi-turbo engine has a water fed cooling jacket around the exhaust manifold to help the engine heat up quicker which has the added bonus of reducing the temperature of the gases before they get to the turbos. I read that on the latest TFSI 2.0 engine in the S3 the gases are something like 178 degrees cooler when they get to the turbo as a result, but can't find the article to post the link.

As the motto goes, every little helps, but I was recommended to avoid start-stop after hard driving and I often consult the oil temperature on the lap timer screen (VCDS mod), to ensure the oil temperature is not hot before switch off. By way of guidance, I can't get the oil above 103 degress C when driving hard, but would like it to be under 100 when I turn off. I have knowledge that 130 is when the car gets upset, but that is Autobahn storming territory which none of us Brits are going to get too and as a result I wouldn't worry too much.

[jbanfie]

Everyone should read and fully understand the following:

http://www.aachener-kolloquium.de/pdf/vortr_nachger/2011/a1.1_wurms_audi.pdf

It's very interesting, but does say that as the exhaust cooling is improved, they can run the engine hotter!!!!

Cheers

[daycartes]

Everyone should read and fully understand the following:

http://www.aachener-kolloquium.de/pdf/vortr_nachger/2011/a1.1_wurms_audi.pdf

It's very interesting, but does say that as the exhaust cooling is improved, they can run the engine hotter!!!!

Cheers

Is this the 21st century edition of the Diet of Worms?

[SGH1]

All useful advice and very informative. Cheers.

[Tripletrouble]

Is this the 21st century edition of the Diet of Worms?
No, I think however you will find it is the 21st century version of the can of worms!

[boof]

This came up on here recently and I'll say the same now as I said then (which is very much against the grain) - every engine builder / performance specialist I've spoken to about my (now previous) performance turbo cars have guffawed at the ideas of turbo timers and letting turbos cool in this age of water cooling and better oils. The bi-turbo unit in the a6 certainly has a water cooling element - not sure about the 2.0's but I'd imagine they do.

It absolutely does no harm to let your car idle to 'cool down' but in my opinion we're long past the days where this should be a concern.

Regarding the failure rate of modern turbos I think this can be more down to :

- The fact there are in general a far, far higher proportion of cars on the road with turbos now. Turbos will fail so by that token we'll hear about it more.

- Extended / 'long life' official oil service intervals. That's a whole different subject in itself..

I wouldn't worry about it at all. I've owned a half dozen turbo cars over the years and never had the sniff of an issue. I don't personally know of anyone who ever has either - at least in unfettled form.

Regardless of if it's technically necessary I also think if you look at your average drivers journey it would be reasonably rare to be ragging the behind off your turbos and then coming to an immediate complete engine off. Most journeys will likely have an element of time towards the end where the driving is, by nature, gentler for a few minutes.

[Tripletrouble]

Extended / 'long life' official oil service intervals. That's a whole different subject in itself..Indeed it is. I have just sold my Mondeo which was serviced every 12k on the dot. The turbo was starting to whine when I sold it.
Now I cannot see how a manufacturer would say 20k is OK for a car to go between oil changes if it knew it wasn't? The bad press would be monumental.
Hyundai state 20k for the i40 and give a 5 yr unlimited mileage warranty so they must have some faith. The sales guy in Cardiff Audi told me quite categorically that I should have my car switched to long life servicing ASAP as I do 20k+ P/A.
Would they do that knowing it will eventually FUBAR the engine?

[boof]

I don't have anything at all to back this up but I'm fairly sure BMW for one have been quietly reducing service intervals heavily for new models as of this year, at least in the NA market. If you're doing 20k per annum would it also be true you will at least be getting the oil changed, time wise, once a year?

Therefore there could be a nice balance there for you. 'Traditional' long life servicing could see you two years between changes for some marques if your mileage was average.

If you're in this thread worrying about turbo cool down - then I would hope you're also on the fixed term 10k scheduling as well..

[Tripletrouble]

Oil would be changed once a year at 20k, yes.
Turbo cool down is not something that worries me as I have a routine when I get home that means the car is in neutral for the last 200 yrds just ticking over.
A bigger concern should be allowing the turbo to spool down after a spirited run so it's not at 100k rpm when the oil supply is cut off!!