Diesel turbo's don't require "spinning" down

Sorry Chris i disagree there, they may not get as hot but DO need cooling down before switch off.

My stepson couldn't see why he was eating turbo's every year, until he drove the last mile 'normally' at low revs (the way a diesel is designed to work) since then he has had no more problems.

When we get a new make of vehicle delivered all the manufactures recommend letting them idle for 30 seconds before switch off.

The problem is the heat soak when you stop moving, so letting them idle pushes cooler oil round the bearings helping to preserve them.

ap0gee i wasn't aware of a water cooled turbo on a car?

ap0gee i wasn't aware of a water cooled turbo on a car?

I'm guessing the expert who wrote the response to the question is referring to 'proper' high-performance cars as regards the water-cooled thing...?

Sorry Chris i disagree there, they may not get as hot but DO need cooling down before switch off.

Then how do you account for the hundreds of thousands of diesel rep mobiles who don't follow this and don't have any problems? The oil pump is constantly circulating oil and unless you come skidding to a halt (on full boost), sufficient hot oil will have been removed from the turbo, imho.

If you wanna do it, then please be my guest, but imho it's just a waste of diesel

Chris

As you yourself suggested the problem could be oil starvation, this can be caused if the engine is just turned off, the turbo's heat soaks into the bearings,

letting it idle however replaces that very hot oil with much cooler oil (and cooler exhaust gasses) so there is less chance of the bearings having no oil in them on start-up. This is why most of the turbo's that go have bearing failure.

To run the engine at a lower speed for the last mile actually saves money, so the penny or two it might cost to let it idle has already been saved,

compared to a £500+ bill to replace a turbo (DIY) it actually makes sense.

I am not trying to make anyone change the way they stop there car, but the OP wanted to know why it had happened so soon.

At least when you understand what the internals are doing you are in a better position to be more mechanically sympathetic.

I know of atleast one car where its NEVER driven slowly, its hammered from the moment its key is turned to the moment the engine is turned off, never given a hint of mechanical sympathy, and the turbo still lasted well over 30k IIRC. The car couldn't have been given more abuse, and it was mapped, and run in using the above technique... so to kill 3 in 15k is simply not possible imho without some kind of other problem.

A man after my own heart

Diesel turbo's don't get anywhere near as hot as petrol turbos and therefore don't require "spinning" down - look at how many diesel repmobiles and taxis are abused and then just switched off. Most make astronomical miles without ever needing to replace the turbo.

Chris

You sure?

Sure I saw someone mention their turbo was glowing after a RR run.

I always let my turbo spin down after a blast, especially a long motorway run. A good 30 seconds idling is a small price to pay for avoiding a £1k bill, even if we're unsure as to the levels of benefit it has.

Why all the fuss anyway? It's only 30 seconds. Better safe than sorry, and it doesn't cost anything to leave the engine running whilst you take your murdering/ leather driving gloves off and take the radio fascia off.

ap0gee i completely missed your #23 post!

It does appear (after Googled'!) that quite a few turbo's are water cooled, you learn something new every day.

I knew they existed just not in cars.

The turbo on my 51 plate astra 1.7 cdti (isuzu engine) was watercooled if i remeber correctly. Im a military mechanic and the number of turbos we change in landrovers is staggering. The vehicles get thrashed all the time they are in use and never allowed to cool for a short period, the vanes/spindles rarely fail but they leak oil like fook and as such smoke really bad and would never pass the emissions checks. New turbo solves it every time. It would save me 3 hours work every time if the lazy gets let them cool for a minute or so!

The PD130 turbo is a KKK one isn't it? And the PD150 one is a Garrett one isn't it?

The upgraded one has stronger shafts and bearings IIRC hence less failures, plus as it's bigger allows more boost. In standard form I imagine they're pretty underworked.

The problem is the heat soak when you stop moving, so letting them idle pushes cooler oil round the bearings helping to preserve them.

I always thought that oil is better when it's at working temperature hence the guide to start up and go as opposed to sitting there waiting like my dad does.

The time the oil takes to get to the turbo from the sump after a hard run it isn't going to 'cool' down that much before it reaches the turbo, IIRC the turbo is the first thing supplied after the filter.

I thought the turbos worked on the fluid bearing principle, no rollers in there, the shaft just runs on a thin film of oil so as long as there is oil it's ok? it costs a lot of money to use ceramic rollers as the steel ones are no good. I think they can use them for slower running machinery but not for the speeds a car turbo gets up to.

I let mine run down for about 15 - 20 secs and then switch off but then i don't really thrash it that often.

Still going strong after 60k

I always thought that oil is better when it's at working temperature hence the guide to start up and go as opposed to sitting there waiting like my dad does.

The time the oil takes to get to the turbo from the sump after a hard run it isn't going to 'cool' down that much before it reaches the turbo, IIRC the turbo is the first thing supplied after the filter.

I thought the turbos worked on the fluid bearing principle, no rollers in there, the shaft just runs on a thin film of oil so as long as there is oil it's ok? it costs a lot of money to use ceramic rollers as the steel ones are no good. I think they can use them for slower running machinery but not for the speeds a car turbo gets up to.

I let mine run down for about 15 - 20 secs and then switch off but then i don't really thrash it that often.

Still going strong after 60k

Your totally correct there mate.

Its not a case of letting the turbo cool.

The kkk turbos have a floating bearing, which needs oil pressure in order to work correctly.

If you think about it this way, you come home from a blast, and your turbo is still spinning at say 5000 rpm. If you switch the engine off, you also stop the oil pump, which in turn cuts the oil pressure to the turbo bearings. this means that the bearing is then running metal to metal. Which isnt good.

_____

john

If you think about it this way, you come home from a blast, and your turbo is still spinning at say 5000 rpm.

But how long does it take the turbo to spin down to very little rpm as surely to stop after a blast you're going to be off the gas for at least 10 seconds while you're slowing down, probably more? Also a turbo will peak at between 80k and 200k rpm so even if it is as high as 5k rpm at idle, it seems in the big scheme of things it's pretty insignificant?

Chris

But how long does it take the turbo to spin down to very little rpm as surely to stop after a blast you're going to be off the gas for at least 10 seconds while you're slowing down, probably more? Also a turbo will peak at between 80k and 200k rpm so even if it is as high as 5k rpm at idle, it seems in the big scheme of things it's pretty insignificant?

Chris

Indeed it is, But id always still let it idle for a few seconds just in case.

Thats where the advantage of a Roller bearing turbo comes in, they dont need oil pressure to spin freely. They wear less and spin up quicker.

I'm worried, I haven't replaced a turbo on mine but it did come with a piece of paper saying it had been replaced before I got it...

my longest mileage turbo car was my Lancia Thema turbo (155,000 miles) that was the 220bhp petrol 2 litre from the integrale....

was still working fine when I got rid.....

*misses his lancia......

i think a point has been missed in this thread , its not only the bearings that need cooling down , but the whole turbo itself , someone mentioned glowing red hot , yes they can do when thrashed (more so on petrols) , so this heat needs to be allowed to dissapate before the engine is turned off otherwise the small amount of oil on the bearing shaft will be fried due to the excess heat in the turbo , the oil will then be a carbon build up on the shaft , not a good situation

also when replacing a turbo , the oil pressure pipe to it has to be replaced , these have been known to block or become partially blocked , hence oil starvation to the turbo

catalysts should be replaced if the oil from the turbo has gone into them , and the whole exhaust system if it was a bad turbo failure, also the intercooler and pipework needs checking for debris, and drained of oil

Well when it went the first time the entire sump went out the exhaust. All that was replaced according to the warrenty sheet was the gaskets, the turbo, the oil and oil filter. The second and third times I never got any paper work but I was told the same things where done.

They said this time they wanted to fit a Garret as they have had loads of KKK's fail on them - but apparantly SUK would not authorise it so its had another KKK fitted.

Hi all

Well I got my car back with new turbo fitted - took the dealer 3.5 days to do the job.

2 year warranty on the new one (parts and labour I think)

I asked what was the dealer price for replacement if it hadn't been covered underwarranty - they said close to £1800

cheers

bren

Hi all

Well I got my car back with new turbo fitted - took the dealer 3.5 days to do the job.

2 year warranty on the new one (parts and labour I think)

I asked what was the dealer price for replacement if it hadn't been covered underwarranty - they said close to £1800

cheers

bren

3.5 days?? Ouch. Doesn't take that long to change a turbo and IC (if indeed they did the IC?) I take it that included ordering the parts and lots of tea breaks?