Discussion
What's the procedure for the 996tt? I've obviously heard about this cool down period before turning off the engine, otherwise the turbos are too hot and the standing oil will burn in the bearings causing damage.
But I can't see this in the manual anywhere, and you don't see people with turbo diesels carefully cooling their turbos down when they've stopped, although I guess their exhaust temperatures are cooler anyhow.
Any science behind this? I idle it for a little while, maybe a couple of minutes if I've been leathering it in the last couple of miles, but usually I'll take it easy for the last two minutes of my journey anyhow and wait a minute, check the oil, turn off the radio, etc, etc.
How can I know I'm doing right?
SM
But I can't see this in the manual anywhere, and you don't see people with turbo diesels carefully cooling their turbos down when they've stopped, although I guess their exhaust temperatures are cooler anyhow.
Any science behind this? I idle it for a little while, maybe a couple of minutes if I've been leathering it in the last couple of miles, but usually I'll take it easy for the last two minutes of my journey anyhow and wait a minute, check the oil, turn off the radio, etc, etc.
How can I know I'm doing right?
SM
kayc said:
Last car i heard of with Turbo over heating problems after thrashing was the Renault 5 turbo which had to idle for a couple of minutes after use.
That's because it was carb fed. Heat soak would vapourise the fuel in the chambers causing problems on hot start - a percolator fan was fitted but it proved to be next to useless as it was drawing in hot hair.
Does, in my own unqualified opinion 
,leaving the engine at idle for 30 secs or so before switching off allow the turbine shaft speeds to slow down enough, so as not to to still be spinning too fast when oil is no longer being pumped through the turbo(s), so therefore not spinning to a standstill unlubricated and causing premature wear on the bearings? Or something like that...
prepares for being told I'm talking total and utter bollox
,leaving the engine at idle for 30 secs or so before switching off allow the turbine shaft speeds to slow down enough, so as not to to still be spinning too fast when oil is no longer being pumped through the turbo(s), so therefore not spinning to a standstill unlubricated and causing premature wear on the bearings? Or something like that... prepares for being told I'm talking total and utter bollox
nervous said:
you could get a turbo timer if youre really worried. though if you live anywhere with even a smattering of crime, id advise caution.
2 mins idling is ample. its only a case of transfering the heat around the system through the liquids. its not overly scientific.
Nervy in sensible post shocker...............
I guess the shaft might go on for a few seconds if you shut down at hight boost but I wonder for how long?
I think the main problem is (said to be) that the castings in the exhaust are hot and boil the oil and water that's in there.
Certainly I recall listening to my old Rover 420GSi turbo boiling up just after I shut down if I'd done it too soon...
SM
I think the main problem is (said to be) that the castings in the exhaust are hot and boil the oil and water that's in there.
Certainly I recall listening to my old Rover 420GSi turbo boiling up just after I shut down if I'd done it too soon...
SM
Yup most diesel manuals advise letting it idle for a period before
shutting down. The wifes Corolla manual actually gives times
accoring to how fast it's been driven distance etc.
With the ALfa I always let it idle to cool the turbo, also
the last 1-2 miles home I short shifted so the turbo was barely spinning.
The bill at 48K for a new turbo for it was around £900 fitted, hence I looked
after it!
shutting down. The wifes Corolla manual actually gives times
accoring to how fast it's been driven distance etc.
With the ALfa I always let it idle to cool the turbo, also
the last 1-2 miles home I short shifted so the turbo was barely spinning.
The bill at 48K for a new turbo for it was around £900 fitted, hence I looked
after it!
c2look said:
Does, in my own unqualified opinion
prepares for being told I'm talking total and utter bollox
That is also my understanding of the main reason for a turbo idling period before shut down.....so that is 2 of us talking bollox.....same reason for not using high revs at start up.
c2look said:
Does, in my own unqualified opinion
prepares for being told I'm talking total and utter bollox
That is also my understanding of the main reason for a turbo idling period before shut down.....so that is 2 of us talking bollox.....same reason for not using high revs at start up.
c2look said:
Does, in my own unqualified opinion
prepares for being told I'm talking total and utter bollox
I think that you're talking total and utter bollox!
I would expect the turbine to spin down very rapidly, i.e. in seconds. The 2 minute wait is all about heat soak - if you've just been thrashing your beastie then the turbo's rotor and casing are very damned hot. A quick shutdown will allow the heat soak to fry the oil in the turbo rotor bearings to carbon, a good way of scoring the bearing surfaces the next time that the turbo spins up. The 2 minutes idling or "driving the last mile like a curb-crawler" allows the turbo to cool down, avoiding this problem.
Raven Flyer said:
Nel has it right.
Simply drive slowly for the last mile or two of your journey and it will be fine to just turn off. Under load, the turbo exhaust casing will be over 700degC. Within 5 seconds of lifting off, it will be sub 400degC. Within one minute, it will be around half that.
oh, yeah. just ignore me being right. fine. thats just fine.
nervous said:Are you having bladder issues today Nervy?
long story short, it wont hurt to let youre car cool down. a better way yet is to pick a point 1 mile from home and always slow down at the point and drive like a vicar. this will do the job nicely.
of course, this will be less effective if you really need a wee.
Nervy do you HAVE a job 
And you want to lay off the Stellas man. You're so pi55ed you're giving sensible advice.
The answer here is wot Nervy sed *faint* *thud*
You should always run the car gently for the last couple of minutes,. If you need to stop after a good pasting (i.e after pulling off (!) the Autobahn) then you should allow to idle for not less than a couple of minutes to allow the heat to be distributed through the oil system.
Ithangyou....
And you want to lay off the Stellas man. You're so pi55ed you're giving sensible advice.
The answer here is wot Nervy sed *faint* *thud*
You should always run the car gently for the last couple of minutes,. If you need to stop after a good pasting (i.e after pulling off (!) the Autobahn) then you should allow to idle for not less than a couple of minutes to allow the heat to be distributed through the oil system.
Ithangyou....
nervous said:
Nel has it right.
Simply drive slowly for the last mile or two of your journey and it will be fine to just turn off. Under load, the turbo exhaust casing will be over 700degC. Within 5 seconds of lifting off, it will be sub 400degC. Within one minute, it will be around half that.
oh, yeah. just ignore me being right. fine. thats just fine.
Stop being so needy ya big poof! Anyone would think that you need recognition on PH to prop up your fragile ego or something!
vesuvius996 said:
Nervy do you HAVE a job
And you want to lay off the Stellas man. You're so pi55ed you're giving sensible advice.
The answer here is wot Nervy sed *faint* *thud*
You should always run the car gently for the last couple of minutes,. If you need to stop after a good pasting (i.e after pulling off (!) the Autobahn) then you should allow to idle for not less than a couple of minutes to allow the heat to be distributed through the oil system.
Ithangyou....
finally...someone who notices that ive been grown up today. all
day no less. i didnt like it though, so im going back to being a tit tommorow.Gassing Station | Porsche General | Top of Page | What's New | My Stuff