Omega Owners Forum
Chat Area => General Car Chat => Topic started by: Auto Addict on 03 August 2014, 07:30:28
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Is it true you should let a diesel turbo idle for 30 secs. before switching off?
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Is it true you should let a diesel turbo idle for 30 secs. before switching off?
It's not good for any turbo'd engine to turn it off straight away after 'enthusiastic' driving where the turbo has been in use. Letting it idle for a short time before turning it off allows oil to circulate the turbos bearing to remove heat from them
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Is it true you should let a diesel turbo idle for 30 secs. before switching off?
It's not good for any turbo'd engine to turn it off straight away after 'enthusiastic' driving where the turbo has been in use. Letting it idle for a short time before turning it off allows oil to circulate the turbos bearing to remove heat from them
Well, you live and learn, thank you :y
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So just like the rest of the engine? :-\
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So just like the rest of the engine? :-\
Looks like it.
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So just like the rest of the engine? :-\
No ..... the oil in the rest of the engine isn't subjected to the same high temp as that around the turbo's bearings
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So just like the rest of the engine? :-\
No ..... the oil in the rest of the engine isn't subjected to the same high temp as that around the turbo's bearings
You live and learn - again :y
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So just like the rest of the engine? :-\
No ..... the oil in the rest of the engine isn't subjected to the same high temp as that around the turbo's bearings
Maybe so, but that's relevant to a turbo, be it petrol or diesel. Why would a diesel turbo get special treatment any more than a petrol turbo.
I wouldn't give an engine any more of a chance to cool down after a thrashing or a pootle, but that's the nature of the speed limits and built up areas on the roads leading to my house.
Obviously after a track day that would "might" be different into pit lane.
But to say any turbo diesel must run at idle for an amount of time after a run would be ridiculous. IMO.
Let's face it if something is over heating, the quickest way to cool to down is to turn it off. Then apply un related cooling such as a fan. Hence the fans run after switch off.
No.....?
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So just like the rest of the engine? :-\
No ..... the oil in the rest of the engine isn't subjected to the same high temp as that around the turbo's bearings
Maybe so, but that's relevant to a turbo, be it petrol or diesel. Why would a diesel turbo get special treatment any more than a petrol turbo.
I wouldn't give an engine any more of a chance to cool down after a thrashing or a pootle, but that's the nature of the speed limits and built up areas on the roads leading to my house.
Obviously after a track day that would "might" be different into pit lane.
But to say any turbo diesel must run at idle for an amount of time after a run would be ridiculous. IMO.
Let's face it if something is over heating, the quickest way to cool to down is to turn it off. Then apply un related cooling such as a fan. Hence the fans run after switch off.
No.....?
I think what Andy is referring to is the spool down time for the turbo be it petrol or diesel,the turbo can be spinning at many thousands of rpm after a burst of acceleration and there is a risk that a sudden engine stop can leave the turbo still spinning without oil being pumped around the bearings :y
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I've always understood that you should also let a TD idle for a while when started from cold so oil is pumped into the turbo. :-\
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The turbo on a car engine will spool down almost instantly and the oil is pumped through the turbo bearings at some rate so if you should burst a oil feed pipe you end up with the sump contents on the road pretty fast.
If it were a bigger engine like a train of which ive driven at a railway preservation you always left the triple pump running for at least 2 minutes to let the turbo stop spinning
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I think what Andy is referring to is the spool down time for the turbo be it petrol or diesel,the turbo can be spinning at many thousands of rpm after a burst of acceleration and there is a risk that a sudden engine stop can leave the turbo still spinning without oil being pumped around the bearings :y
Yes, and, in addition, the turbo will be very much hotter than any other part of the engine to which the oil circulates. Shut it down at this temperature and the residual oil in the bearing might get hot enough to scorch, leaving deposits on the bearing which will result in its' untimely demise. Leave it idling and it will continue to be cooled by the oil.
Probably only needs to be 30 seconds or so without load but, in a scenario where it comes from towing a caravan on a motorway, into a service station and engine off.. might be good practice to let it idle a little. :y
Some turbo cars have a water cooled turbo with either a thermo syphon or an electric pump that runs after the engine, but many have only an oil supply, which doesn't allow any flow after shutdown.
It goes without saying that petrol or diseasel is irrelevant, as the turbo is pretty much identical.
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I guess also that turbos are generally mounted high up, so that the oil will drain out quickly. :-\
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So just like the rest of the engine? :-\
No ..... the oil in the rest of the engine isn't subjected to the same high temp as that around the turbo's bearings
Maybe so, but that's relevant to a turbo, be it petrol or diesel. Why would a diesel turbo get special treatment any more than a petrol turbo.
I wouldn't give an engine any more of a chance to cool down after a thrashing or a pootle, but that's the nature of the speed limits and built up areas on the roads leading to my house.
Obviously after a track day that would "might" be different into pit lane.
But to say any turbo diesel must run at idle for an amount of time after a run would be ridiculous. IMO.
Let's face it if something is over heating, the quickest way to cool to down is to turn it off. Then apply un related cooling such as a fan. Hence the fans run after switch off.
No.....?
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It's not good for any turbo'd engine to turn it off straight away after 'enthusiastic' driving where the turbo has been in use. Letting it idle for a short time before turning it off allows oil to circulate the turbos bearing to remove heat from them
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So, 99 times out of 100, no, not necessary.
Unless your drive way is directly at the end of a motorway slip road after hard engine use. ::)
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So, 99 times out of 100, no, not necessary.
Unless your drive way is directly at the end of a motorway slip road after hard engine use. ::)
yes Chris ................. :-X
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Ok thats all logical but im going to upset it all,how come my transit with eco stop start will turn off if i get stuck in traffic,or stop at lights after long drive,and it shuts engine off...so all seems pointless to let it idle after a long drive ,ecu knows best lol :)
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Ok thats all logical but im going to upset it all,how come my transit with eco stop start will turn off if i get stuck in traffic,or stop at lights after long drive,and it shuts engine off...so all seems pointless to let it idle after a long drive ,ecu knows best lol :)
we have a poxy KA at work with a turbo bolted to it and that does the same with eco stop :y
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So, 99 times out of 100, no, not necessary.
Unless your drive way is directly at the end of a motorway slip road after hard engine use. ::)
yes Chris ................. :-X
Good, that's that sorted then. :)
;D
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From my understanding, and this is from conversations with people in the trade, its to do with the tree huggers. A manufacturer cannot recommend to leave an engine running unnecessarily due to emissions. They had to use better oils that wouldn't leave as many deposits on the turbo bearings which also lead to better designed engines. Its the same as they done away with the autolubes on new trucks as the small grease deposits that drip from stubs etc is bad for the environment, so they used rubber bushes on spring shackles that now are replaced at least every four yrs and stubs that still take grease anyway.
That's also why that I see so many vag tdi turbos being changed due to bearing failure. The manufacterer has to be seen to be protecting the environment over looking after an engine.
Only my view which people don't have like but its what I think anyway.
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So what happens if you have a twin scroll turbo?
Its spinning for longer and therefore is likely to be hotter, so do you have to leave that ticking over for a longer period of time??
But then if you do leave it ticking over how do you stop heat soak?
:-)
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Heat into the turbo comes from exhaust gases, friction in the bearing and the work done by the compressor. All 3 of these are negligible at idle when the exhaust gases are cool, since the engine is not under any significant load, the bearing generates little heat since the turbo will only be spinning slowly, and the compressor is not producing boost but having cool air sucked through it by the engine.
Heat soak is only ever going to come from the engine, which is limited to 90 odd Celcius by the cooling system In turbo terms, that's very cool. ;)
The turbo has very little rotational inertia (otherwise it's take an age to spool up!), so the instant you stop the engine, and the flow of exhaust gas stops, the turbo stops.
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So years ago in days gone by, when turbos were high strung and attached to what would be considered basic engines (little if any engine management) you suffered a few things the most significant being Very high exhaust temperatures resulting in very high turbo temperatures.
Add to this basic lubrication setups and you needed some cold no low air to cool the unit down for 30 seconds or so whilst the bearings remained lubed (often with the waste gate open to minimise spindle speed).
Modern setups are much better, exhaust temperatures are significantly lower (thanks to modern engine control), oil lube systems much better and the turbos often have some oil reservoir capacity in them and the bearings are much better. As a result, its not needed, in fact the most highly strung engines often have water coolers in them and electric lube pumps.
So for a modern turbo petrol, I would say only needed if you have spanked it just before stopping (often taking it easy the last mile or so will be more than enough)
Throw in a diesel engine where the exhaust temperatures are even lower and the need totally goes away. :y
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If it were a bigger engine like a train of which ive driven at a railway preservation you always left the triple pump running for at least 2 minutes to let the turbo stop spinning
Key reason for keeping the triple pump running is to keep the oil lube going for a period plus it also keeps water circulation, two minutes is excessive though, 30 seconds is more than enough and ensures you don't take to much out of the (often tired in preservation hence its a balance) batteries ready for the next start. :y
On the likes of the Sulzer and EE engines, the turbos are so huge and barely moving at EO or notch off they stop spinning before the engine does (including the baby ones on the likes of the V8's on the c20's).
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So years ago in days gone by, when turbos were high strung and attached to what would be considered basic engines (little if any engine management) you suffered a few things the most significant being Very high exhaust temperatures resulting in very high turbo temperatures.
Add to this basic lubrication setups and you needed some cold no low air to cool the unit down for 30 seconds or so whilst the bearings remained lubed (often with the waste gate open to minimise spindle speed).
Modern setups are much better, exhaust temperatures are significantly lower (thanks to modern engine control), oil lube systems much better and the turbos often have some oil reservoir capacity in them and the bearings are much better. As a result, its not needed, in fact the most highly strung engines often have water coolers in them and electric lube pumps.
So for a modern turbo petrol, I would say only needed if you have spanked it just before stopping (often taking it easy the last mile or so will be more than enough)
Throw in a diesel engine where the exhaust temperatures are even lower and the need totally goes away. :y
Ive never let a turbo diesel idle before switching it off and never had a problem with the turbo....except that wnkr of a Fiat....which went thro 2 turbo's but that was oil starvation to the turbo as it turned out...
But in AA's case, when he is towing the tin tent on the motorway....the turbo maybe working hard, especially on an uphill climb.....and if he has to nip into the services to use the loo, it maybe worth leaving mrs AA in the car with the engine idling whilst he pops off the use the facilities (you know these pensioners are like for using the loo) ::) ;D ;D
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So years ago in days gone by, when turbos were high strung and attached to what would be considered basic engines (little if any engine management) you suffered a few things the most significant being Very high exhaust temperatures resulting in very high turbo temperatures.
Add to this basic lubrication setups and you needed some cold no low air to cool the unit down for 30 seconds or so whilst the bearings remained lubed (often with the waste gate open to minimise spindle speed).
Modern setups are much better, exhaust temperatures are significantly lower (thanks to modern engine control), oil lube systems much better and the turbos often have some oil reservoir capacity in them and the bearings are much better. As a result, its not needed, in fact the most highly strung engines often have water coolers in them and electric lube pumps.
So for a modern turbo petrol, I would say only needed if you have spanked it just before stopping (often taking it easy the last mile or so will be more than enough)
Throw in a diesel engine where the exhaust temperatures are even lower and the need totally goes away. :y
Ive never let a turbo diesel idle before switching it off and never had a problem with the turbo....except that wnkr of a Fiat....which went thro 2 turbo's but that was oil starvation to the turbo as it turned out...
But in AA's case, when he is towing the tin tent on the motorway....the turbo maybe working hard, especially on an uphill climb.....and if he has to nip into the services to use the loo, it maybe worth leaving mrs AA in the car with the engine idling whilst he pops off the use the facilities (you know these pensioners are like for using the loo) ::) ;D ;D
You know nothing, I'm on tablets for that.
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as long as he is gentle along the sliproad and parking area, it should have slowed the turbo spinning and cooled a bit,