Hi all (from New Zealand... yep, we do have Cits here!)
I've just purchased my first Citroen - 1993 XM 2.0 turbo. I'm gong to write a few things about it - how great it is, etc- once I've taken it to the local indy guy for a check up.
One question before I do that. It has no turbo timer. The book says to let the egine run for a few seconds before turning off the engine. But I always thought turbos ran for a few minutes before shut down. I've been running mine for 4 mniutes before shut down. A fan keeps going for a few minutes after that.
Has anyone fitted a turbo timer (so you don't have to hang around to manually shut off)? Or don't you need to worry about it with the XM?
Full Version Turbo timer
HI Ross,
Welcome to club-xm and congratulations at being the first 'petrol' poster.
I have a diesel myself and therefore don't have first hand knowledge of the petrol turbo. However, the theory should be the same. The spinning shaft of the turbo sits on a bed of pressurised oil fed from the oil pump. The shaft spins at up to 13000 rpm but there is no metal to metal contact since the oil film keeps the surfaces apart.
The reason why you're advise to keep the engine running for a short time after coming to a stop is that when the engine is turned off, the oil pump stops. If the turbo is still spining at a high rate of knots then, without the protective layer of oil, the shaft will run dry on the bearing surfaces. Do this too many times and the turbo will pack in. Keeping the engine running for a minute or so allows sufficient time for the turbo to slow down before stopping the oil pump.
There is another, secondary reason for having some idle time after you come to a stop. If you have just finished a half hour high speed burn then the turbo is likely to be glowing a dull cherry red (or bright cherry red if you're a bit of a tearaway ;-). The idle time is needed to let the turbo body cool off to prevent the heat carbonising the stationary oil on the shaft.
There's no timer as such since it's a human decision to keep the engine running for a little while.
Hope this helps.
cheers
noz 8)
Welcome to club-xm and congratulations at being the first 'petrol' poster.
I have a diesel myself and therefore don't have first hand knowledge of the petrol turbo. However, the theory should be the same. The spinning shaft of the turbo sits on a bed of pressurised oil fed from the oil pump. The shaft spins at up to 13000 rpm but there is no metal to metal contact since the oil film keeps the surfaces apart.
The reason why you're advise to keep the engine running for a short time after coming to a stop is that when the engine is turned off, the oil pump stops. If the turbo is still spining at a high rate of knots then, without the protective layer of oil, the shaft will run dry on the bearing surfaces. Do this too many times and the turbo will pack in. Keeping the engine running for a minute or so allows sufficient time for the turbo to slow down before stopping the oil pump.
There is another, secondary reason for having some idle time after you come to a stop. If you have just finished a half hour high speed burn then the turbo is likely to be glowing a dull cherry red (or bright cherry red if you're a bit of a tearaway ;-). The idle time is needed to let the turbo body cool off to prevent the heat carbonising the stationary oil on the shaft.
There's no timer as such since it's a human decision to keep the engine running for a little while.
Hope this helps.
cheers
noz 8)
A bit more about turbo timers on XMs. I was curious about turbo timers - they're very common in New Zealand, mainly on all the Japanese "sports" cars that the kids drive. They allow you to set a time (10 secs-10 minutes) that your engine can be left running to cool things while you leave the vehicle. I asked a general question on this post about that, and got a reply from Norrie. Not that I don't trust Norrie's advice, I asked my local citroen guy. He said they're unnecessary for the XM, and he wouldn't recommend one. So I'm not going to get one - I'm prepared to sit around in my car (coz it's so darn comfortable) and wait for things to cool down a for a few seconds (but not the 3-4 minutes that I have been doing).
You see, I've just bought my car, and I'm a bit paranoid. It's done 144,000 miles. I'm going to write a bit more about it in a general post soon.
Cheers
You see, I've just bought my car, and I'm a bit paranoid. It's done 144,000 miles. I'm going to write a bit more about it in a general post soon.
Cheers
Ross,
You are quite right. My experience of turbo's is limited to the 2.5TD I have at the moment.
I asked around after I read your post and most of the high spec Japanese cars do have run on timers as you say.
Apparently you park the car, turn the ignition key, take the key out, get out of the car, close & lock the doors and walk away with the engine still running ! - very disconcerting for the unaware.
The reason for the run-on was not explained but the principle can't be wrong. The two reasons remain as
1)allowing the turbo shaft to slow down and
2)allowing the cold incoming air to cool down the body of the turbo.
Whilst your Citroen guy says he doesn't recommend one I think a bit of common sense is the best here. If you've just finished some time trials at Brands Hatch and pull into the pit lane - you'd be well advised to keep the engine running for a couple of minutes for the above reasons. However if you're just back from the local paper shop having never got above 30mph then switching the engine off as soon as you stop wouldn't appear to have any long lasting effect.
Cheers
noz 8)
You are quite right. My experience of turbo's is limited to the 2.5TD I have at the moment.
I asked around after I read your post and most of the high spec Japanese cars do have run on timers as you say.
Apparently you park the car, turn the ignition key, take the key out, get out of the car, close & lock the doors and walk away with the engine still running ! - very disconcerting for the unaware.
The reason for the run-on was not explained but the principle can't be wrong. The two reasons remain as
1)allowing the turbo shaft to slow down and
2)allowing the cold incoming air to cool down the body of the turbo.
Whilst your Citroen guy says he doesn't recommend one I think a bit of common sense is the best here. If you've just finished some time trials at Brands Hatch and pull into the pit lane - you'd be well advised to keep the engine running for a couple of minutes for the above reasons. However if you're just back from the local paper shop having never got above 30mph then switching the engine off as soon as you stop wouldn't appear to have any long lasting effect.
Cheers
noz 8)
The info the others are all very good advice to follow !!!!!
Do what you have been doing in the past a bit of fuel is cheaper than a new turbo
That is the most common way of keeping your turbo lasting longer than just turnong the engine off like a lot of people do.
Forget what the nips do with there cars no needs to waste your money keep it for more fuel (You will need it with a petrol turbo)
Good luck
It's illegal to walk away from a running vehicle -
Endorse what Noz said about cooling, oil carbonising on the turbo shaft etc
but some reason needs to be applied - if you red-line it up to your house
you should let it run for a minute or so - most turbos are water-cooled as
well as cooled by the flow of oil - and the oil flow alone is massive - and
these carry heat away from the bearing area - so about a minute would
be good - if the turbo was glowng, there will be heat-soak into the bearing
housing; usually the under-bonnet temperature will cause the fans to run.
Just need to watch the plot intelligently.
Otherwise, if I arrive briskly but not banshee, I give it 10-15 secs.
G/.
Endorse what Noz said about cooling, oil carbonising on the turbo shaft etc
but some reason needs to be applied - if you red-line it up to your house
you should let it run for a minute or so - most turbos are water-cooled as
well as cooled by the flow of oil - and the oil flow alone is massive - and
these carry heat away from the bearing area - so about a minute would
be good - if the turbo was glowng, there will be heat-soak into the bearing
housing; usually the under-bonnet temperature will cause the fans to run.
Just need to watch the plot intelligently.
Otherwise, if I arrive briskly but not banshee, I give it 10-15 secs.
G/.
This is a "lo-fi" version of our main content. To view the full version with more information, formatting and images, please click here .