How Long Do You Wait, before turning off turbodiesel?

My friend told me lately that you should wait a while before turning off the engine in turbodiesel.
The question is what does this WHILE correspond to?
One minute, more minutes, less?

Please let me know.

As a hile mileage and short journey driver, on the xm diesel dont worry, its usually to allow the turbo to cool so as not to cook the oil in its bearings, not a worry on a xm the turbo does not get as hot as most normal cars, even with hard use

Spoken as someone who really did everything by the book, under the heading of 'dont...'

I have always turned mine off immediatly and have never had to replace a turbo, including a CX 266k miles and an XM at 292k miles. I think this idea comes from turbo petrol engines (excuse the language) as if driven hard the turbo's can get red hot! Diesels tend to have a much more way of relaxed life.

Peter.N.

yeah but even the manual(which I am so cursed to have in German:D) states that you should wait a while before turning the engine off...:/

This post has been edited by sophie on December 30, 2008 12:43 am

Sorry, havn't read the manual That would have been printed nearly 20 years ago when turbo diesels were comparativly new. If you thrash it and then abruptly turn it off while still very hot, repeatedly, then there could be a problem, but the majority of diesel owners dont drive like that. I can only go by my own experience, turbos very rarely fail on theses engines, for any reason, I have never had to replace one in about 20 years and half a million miles of driving them.

Peter.N.

Hi Sophie

You need to wait momentarily after the engine has returned to idle, the reason is two fold, first as Lez has said it is to allow the turbo to cool to stop the oil burning onto the bearings when the engine/oil flow stops, the other reason is to let the turbine slow down before the oil supply is removed by turning the engine off, the turbine shaft runs on a film of oil and if the turbine is spinning fast when you turn the engine off it will increase the rate of wear on this shaft and its bearing points, so to get to the point let the engine drop to idle then wait 3 to five seconds and switch off.

Regards
D

Hi Sophie

I live barely two minutes off the motorway, so my motor is always pretty warm by I get home and any cooling down the turbo gets is in that last two minutes to home ---- never had any issues at all. Wouldn't lose any sleep over it. Much, much more important in my opinion are regular oil and filter changes. Do mine every 3000 miles regardless of what the book says.
Incidentally, see yours is auto --- don't forget to change the fluid in there, as well. If you browse the forum you will find various threads regarding the auto boxes.

Mike.

My recollection is the same as Dean's, give it a few seconds to let the turbine slow before you cut off the pressure oil supply from the engine.

Of course you are all right! if it was that important to let the turbo spool down and there was that much risk cit would have fitted a turbo timer which they havnt because a derv doesnt reach those sorts of temperatures but leting it spool down aint gona hurt and will extend the life of the indistructable turbo. Onthecut's coments are more important though, concentrate on regular oil changes.

D

This post has been edited by dean on December 30, 2008 05:35 pm

ok, thank you guys, you made it all clear
Thanks a lot!

Ive heard this before, it makes sense i supose but its not something i worry about with my Turbo Diesel. As said its servicing you need to concentrate on the most.

Funny this has just cropped up on the FCF too, here is the quote:

"Owners of cars with a turbo, including diesels, may or may not know that it is considered wise to allow the engine to idle for a while after a long, fast run. This allows the turbo to cool down a little (with oil still circulating) and not "cook" after the engine is turned off. The following quote is from Wikipedia:
"After high speed operation of the engine it is important to let the engine run at idle speed for around one to three minutes before turning off the engine. This lets the turbo rotating assembly cool from the lower exhaust gas temperatures. Not doing this will also result in the critical oil supply to the turbocharger being severed when the engine stops while the turbine housing and exhaust manifold are still very hot, leading to coking of the lubricating oil trapped in the unit when the heat soaks into the bearings and later, failure of the supply of oil when the engine is next started causing rapid bearing wear and failure. Even small particles of burnt oil will accumulate and lead to choking the oil supply and failure. Oil coking is completely eliminated by foil bearings. This problem is less pronounced with turbochargers used in diesel engines, due to the lower exhaust temperatures and generally slower engine speeds. It is usual for the manufacturer to specify a 10-second period of idling before switching off to ensure the turbocharger is running at its idle speed to prevent damage to the bearings when the oil supply is cut off."

So, if you didn't know already, now you do"

The critical words there are 'high speed operation', doesn't apply to me.

I was aware of this issue, but besides that I've found that when I park somewhere, as long as I'm not in a mad rush, for example if I'm arriving home, or at work, then generally the engine will idle for about 30 seconds or so while I take the seatbelt off, gather my stuff, turn the radio down, get the wee one out of her car seat etc etc. I always do everything first and turn the engine off last thing before I get out.
So unintentionally, I've always done that. I guess its something probably overlooked by non-mechanically minded owners of turbo cars though...

Ciarán

let me give you a kick in the right direction......... the kind and knowledgable gentlemen on here (splutter !!) are saying the right thing......oil changes regularly are very important. but let me get technical for a min....."Clean combustion resulting in clean oil (assuming it has the proper grade, not some cheap concoction) is essential not only for the engine but for the turbo as well. Most people are not aware that a turbo can be--and actually should be--cleaned every 150,000 km or so. This procedure will make it last forever.

To clean it, the turbo should be removed from the manifolds, dissasembled to pieces which are then cleaned thoroughly of carbon and crud deposits. This involves mostly the bearing case, the bearings themselves, the shaft, and the heat sheild on the hot side. The shaft should also be re-balanced when the whole unit is put together again, although with some attention to detail this can be avoided. It is essentially the same process a turbo rebuilder service would do except you need no spare parts.

If you have a turbo seizure, don't think of driving with it even temporarily. Also, for obvious reasons the turbo should not be removed (open manifolds), nor should the intake be bypassed and the turbo left to blow into the atmosphere (over-revving will occur because it will not reach waste gate pressure at any rpm). If a working turbo needs to be disabled it's actually safer to put a piece of pipe at the pressure output and plug it at the end, leaving a very small hole (say 0.5 cm, unfortunately this will result in lots of noise) thus creating a small reservoir and something for the turbo to do without revving itself apart. Merely pulling out the manifold pressure tube that goes to the compensator on the pump will not disable the turbo--it will still work, albeit at a much lower efficiency.

If exhaust gases end up hitting a seized turbo, they eventually burn off the blades of the turbine and the debris ends up in the converter, not to mention the overheating of the turbo itself. There are people who overhaul turbos: this will mean a new set of hydrodynamic bearings, oil seal rings, a new shaft and a new set of turbine (and possibly compressor) blades. In any event it will be cheaper than a new one.

Alternatively, you can look at scrapyards for the same basic model, and have the refurbishing people do a 'make one out of two' job, which actually only involves exchanging the parts that attach to the manifolds, plus cleaning the salvaged turbine.

The main reasons a turbo can fail are the following: it is not allowed to spin down before oil pressure drops. This results in the spinning shaft crashing into the hydrodynamic bearings. This in itself may not damage the bearing or the shaft, unless it happens repetitively. The oil that remains there offers some lubrication for a while until its temperature reaches a very high level because of drag to the shaft; this will produce a local carbonisation. This builds up until it either damages the soft bronze bearing the next time the shaft drops or until enough carbon builds up to seize the turbine. The situation is much worse if the turbo was under a great deal of strain just before this, the temperature of the shaft being quite high. Always allow then engine to run on idle for a minute or two to let the turbo cool down before you switch the egine off, especially after highway runs.

If the oil seal wears out on the hot side, the oil will pour out between the seal and the heat shield, getting burned. The resultant crud produces drag and more heat on the shaft, and as it builds up, it may actually end up pushing out the heat shield as it expands under heat. The resulting impact on the hot side rotor will brake it down. The added (signifficant) drag may then literally burn off the rotor blades. This is usually caused by contaminants in the oil carbonising on the oil seal and wearing it out, This is responsible for most turbo failures on a diesel. The occasional cleaning of the turbo will prevent this failure completely (unless the engine and the turbo are already on their last legs)." so changing the engine oil will be your best bet. and if your car is used on motorways or high stress stuff ie caravanning , towing heavy trailers up hills etc please remember to allow the turbo to cool down before you turn of the engine for a minute or so....every little bit of care helps and will not hit your wallet......was this enough info to answere your question??