Would someone be kind enough to explain when it is necessary to
Spool down the turbo. Is it recommended after short journeys of say 5 miles in town driving conditions? or only after motorway trips. Your advice would be appreciated.
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I *think* HJ recommends idling any turbo engine, but particularly diesel turbos, when it has been at full temperature for any length of time, e.g. a motorway run, for a couple of minutes to 'simmer' the oil round the turbo bearings. Other back roomers will know more than me, as I drive expensive petrol engined cars.....
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Hoseman, it's necessary to leave the engine running so that the oil feed to the turbo's bearings is still active - if you turn off immediately the turbo will be spinning down with no oil feed, and this can result in the bearings being damaged. Around town I doubt that this will ever be a problem, but sustained motorway speeds will be, so if you pull off into a service area it's wise to let the engine tick-over for 30-60 secs, to allow the very hot turbo to run down with oil pressure maintained. That said, you won't often see this happen, but it is good practice.
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www.honestjohn.co.uk/forum/post/index.htm?t=31653&...f
then follow the links to more HJ threads within the one above
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Idling the engine after a period of hard driving is probably very sensible and the figure of 30-60 secs should be okay.
On my previous car, (turbo diesel) I removed the turbo outlet pipe and observed how the turbo spooled up and down visually. On revving the engine hard and letting the revs die back the turbo slowed to virtually a standstill almost immediately.
So unlike turbos of yesteryear there is no chance that it may windmill on for ages as I beleive used to be the case. So 30 seconds should be fine.
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I think that people thinking in terms of the shaft spooling up or down may be misled.
I would argue that the vital function being performed by allowing the engine to run for a while before shutting off is cooling.
If you stop a hot engine, the turbo is soon enough spinning slowly, but there is still lots of heat energy left in the turbine and casing. Instead of the oil passing through the oilways quckly, picking up a little heat on the way through, you have a static pool of oil which wouldn't take a huge amount of energy to begin to seriously overheat. So, next time you start up, you don't have a nice free clean oil supply, instead your oil has to struggle through the carbon layer left after the last "fry up"
Number_Cruncher
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My old Audi had an after run pump that kicked in about 30 secs after the engine had been turned off to pump water through the turbo. It ran for a few minutes ensuring that the turbo didn't overheat.
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Many thanks for your help and information on this subject.I was concerned about all the adverse articles about turbo charger problems and I am trying to avoid them.
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