Every so often someone here repeats the oft-quoted advice to idle or 'simmer' a turbocharged engine before switching it off. While I understand the principle that this allows the turbo to cool while the oil is still moving, I'm not so sure how often this will be necessary in real use.
Most journeys begin and end in areas where only low speeds are possible. My regular run features 75 miles of M40 but has a good ten minutes at either end where speeds are much lower. When I get to work or home, I reverse the car into its space. It's hard to see how a minute's idling is going to cool the turbo significantly after that.
In fact, the only situation I can think of where i might stop the engine before the turbo has had a chance to cool naturally is at French motorway service area, where it's possible to pull up, nose first, within a minute of travelling at 130 km/h. On these few occasions, I generally remember to let it run for a bit, but it's a tiny fraction of the times I've stopped my car. Does anyone here encounter situations more often where this technique is actually necessary?
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I agree the technique is rarely needed, but I will do it when pulling into a service area.
The perceived wisdom is turbo diesels run cooler than petrols, so it's not as critical with a diesel.
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When the engine has been run at or near full output, e.g. a long climb in Alpine regions, or a track session, and it hasn't been possible to trundle for a few miles: yes. Running at 70-ish mph requires something of the order of 35hp: barely taking breath, exhaust gas temperature well down, and turbo also. There is an awful lot of twaddle on this, especially as the exhaust temperature of diesels is somewhat lower than petrol engines.
Edited by Honestjohn on 09/02/2010 at 06:15
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I've never read of premature turbo failure on a petrol engined car on here, always diesel, how come?
up
Edited by Honestjohn on 09/02/2010 at 06:15
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So add to that that most diesels with oil cooled turbos hold less than 5L of oil and most of there drivers never check levels so many are running around a litre down on oil and half a litre on coolant and wonder why their turbos fail waiting for the idiot light to flash up on the screen.
I bet if you were to survey a motorway service station less than 1 in 100 would idle before switching off
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There will be people who live in hilly areas who's speeds may well be low but who's turbo may have been working it's little cotton socks off, unless i've been travelling very slowly or manouevering speeds for several minutes my motor always gets to cool down and swmbo is just as sympathetic.
I give the turbo a chance to warm up too before asking it to work hard, same as with a cold engine i hate hearing the sound of tortured engine being forced to scream away having started from freezing cold seconds before, the same folk you just know would pull up in the services and switch straight off.
I'm going to stick me neck out here...up until the last ten or twelve years it was virtually unheard of for a Diesel turbo to blow or seize despite most users thrashing the living daylights out of the engines and not allowing any cool down time, i realise they were less common in those days in car sized engines.
The growth industry in turbo failures has coincided with extended service intervals (and the cars involved seem to have common turbo failures) and the use of oils suitable for both petrol and Diesel engines whereas before most Diesel engines used Diesel specific oils changed at around 6K...and on that note i make no comment for i'm off to bed..;)
Edited by gordonbennet on 08/02/2010 at 22:21
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Have been driving Turbo cars for the last 12 years, 3TDs and one Petrol.
Never bothered but . . .
. . . the last couple of minutes both going home and to the office is in 30 areas so the engine is just above idle.
The Vetra was 20 months old with 56k when I resigned
THe Passat 1.8T had done 96k
The Honda Accord reached 125k
The Octavia is coming up to 2 years old and has done 50k.
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When I asked BMW about this, I was informed that there was an electric oil pump that continued to circulate oil through the turbos to prevent this problem, and if you open the bonnet at the end of a journey, you can hear a faint buzzing noise which I assume is the pump.
Is this right? (It's a 335D)
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There are posts on the VAG sites about the effects of this on the slightly older 1.8T and 2.0T engines. Apparently, even though the turbo may not fail straight away, the little 'stones' of carbonised oil get pushed through to the sump, where they finally end up impacted in the oil pick up strainer. Over time this accumulation can apparently restrict oil flow to the pump.
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I always do this without fail but my turbo on an unchipped vw 130pd tdi went ping at 34000 miles. Variable vane turbos fitted to most modern Diesel engined cars are an awfully lot more complicated than the wastegated turbos on petrol cars. I think my turbos issue was a sticking vane: banshee shriek and sudden total loss of power rather than catastrophic blowup.
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Back in the days of the Renault 18 turbo, early 80s?, the Garda in Ireland got a few of them and they, the Guards that is, had a reputation for wrecking the turbos.
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