Cooling down?

[edwin98]

I have my audi s3 for 5 weeks now and i love the car. Before this i'v drivin a corrado vr6, honda fireblade and a seat ibiza. The s3 is simple the best. Only it is my first turbo charged car. I now it is importand to warm op slowly the engine. But how about cooling down the turbo? Some people say it is importand that when you stop you don't turn the engine of immediatly? Is this so? What can you do best? Our is there no problem at all?

My car is only equipped with an other ecu (250 pk i think, the say) and airfilter, all the rest is standard.

 

[Gambba]

Edwin, whereabouts are you from in the Netherlands? Maybe I've asked before...??!!

Anyway, yes cooling down is very important for a turbo, normal practice is to take it easy for the last 10 minutes of your journey....but I find this hard to do, so just spend 2 minutes with the car at idle when parked up.

I would say the better of the two is to let the car idle for a couple of minutes before switching off, but it does depend on how much you thrash it.

 

[mramage]

Hi Edwin. It's not quite so bad with the S3. There is a pump which keeps circulating water after you stop the engine. It helps cool the turbo.

If I come off the motorway to services I sit for about 3-5 minutes before shutting it off. I also drive a little slower in the last mile to the service, if possible. To see why, try driving at 120KPH for 5-10 minutes at night, then stop and open the bonnet. It'll be easy to spot the turbo /ubbthreads/images/graemlins/grin.gif

It's worth noting that a lot of heavy acceleration in town driving is just as bad though.

 

[Gambba]

Put it neutral before getting out though is a good idea...I believe. /ubbthreads/images/graemlins/grin.gif

Greedy do a turbo timer, but save your pennies and just spend a little time cooling it down.

 

[edwin98]

Think the same !

Thanks

 

[mramage]

[ QUOTE ]
Gambba said:
I agree to a certain extent with what you say Seizure, but I disagree on some points. The turbo will not increase in temperature when the engine is at idle with no load and nor will the engine, this cannot generate heat it's physically impossible. The engine is at it's hottest when under load regardless of moving or not, yes the air flow assists, but then that's what the fans are for!



[/ QUOTE ]

Surely letting an engine idle results in heat soak, coupled with the engine itself producing even more heat, which isn't being removed through the normal method of air while driving? Happy to listen to a full explanation Gambba, since you work in engineering /ubbthreads/images/graemlins/beerchug.gif

That's one reason why I only let the car idle if I think the turbo will be glowing hot.

Under most circumstances it's very gentle driving before switching it off anyway. i.e. Parking after coming off a low speed limit road. Cases where idling may cause increased heat build up.

I don't recall reading anywhere in the manual about turbo cooling, so I guess it's down to a bit of common sense.


/ubbthreads/images/graemlins/beerchug.gif

 

[Gambba]

Ok, when driving the fans are next to useless becuase the airflow created at high speed is more than the fans could possibly produce. So when driving slowly or stopped at Idle this is where the fans really come into there own. Now you consider when the engine is at it's hottest, when it's at full chat under load, so this is when it needs most cooling, where as idling produces relatively small amount heat.

So with the above in mind how could the engine possibly build up heat when stopped idling? Answer it can't, whilst the fans are blowing and the coolant is recirculating is has no choice to cool down. As long is there is air flow you will have cooling, thus no heat soak.

 

[Seizure]

[ QUOTE ]
Gambba said:
The turbo will not increase in temperature when the engine is at idle


[/ QUOTE ]
Not after some enthusiastic driving it won't, but from cold it will. It's relative from that respect. But bear in mind a turbo off boost is a restrictive device, so some heat soak will occur.

[ QUOTE ]
Gambba said:
nor will the engine,


[/ QUOTE ]
Yes it will, otherwise your engine wouldn't get up to working temperature if you left it idling, which it does. It can even get the fans to kick in i.e. when stuck in traffic.

[ QUOTE ]
Gambba said:
The engine is at it's hottest when under load regardless of moving or not,


[/ QUOTE ]
Granted, but what about heat soak. Some of that heat will still be retained when you slow down/stop.

[ QUOTE ]
Gambba said:
yes the air flow assists, but then that's what the fans are for!


[/ QUOTE ]
The fans are there for the cooling system. Any additional airflow through the engine bay is a bonus. And bear in mind the turbo has an engine block between it and the fan.

[ QUOTE ]
Gambba said:
I let my car cool down for a couple of minutes for the simple reason is that while the fans are operating and the water pump is pumping then that means everything is being cooled, not heated up.


[/ QUOTE ]
That's providing the fan is running when you stop. If you only leave it for 30 seconds the coolant may not hit the temp at which the fans kick in, therefore you are putting more heat in there.

[ QUOTE ]
Gambba said:
I would strongly disagree about turbo's being designed and built to withstand abuse,


[/ QUOTE ]
I didn't say they were designed to withstand abuse. I said they were designed to withstand working temperatures.

[ QUOTE ]
Gambba said:
I have seen extremely large and expensive diesel turbochargers fecked up because the operator just jumped out of the machine without a cool down.


[/ QUOTE ]
Everything can be broken. That's why I said it does need to cool down if it's glowing, but if it's been subjected to normal driving conditions it doesn't. Hence the "That's what it was designed for" bit.

[ QUOTE ]
Gambba said:
keeping the turbo lubed and cool is essential for the bearings when shutting down. The turbo on the car does not stop turning just because you leave the car to idle, it will continue to rotate and lubricate itself, and when we say turbo spooling up we don't mean it goes from a standing start, we just mean the time it takes to go from it's idle speed up to 180,000-200,000 rpm.


[/ QUOTE ]
I agree. That's why you shouldn't blip the throttle then shut the engine off with the revs above idle. I realise the turbo is spinning, relatively slowly compared to when it's boosting, but leaving it there spinning slowly with the least amount of oil pressure feeding it is probably more detrimental than just turning the engine off, saving it from 2-3 minutes of slow operation in a low oil feed situation.

[ QUOTE ]
Gambba said:
Most turbo failures are down to lack of lubrication to the bearings....this is a fact!


[/ QUOTE ]
Again, I'm with you. Usually caused by people who blip the throttle on start-up when all the oil has drained from the turbo - The oil hasn't had chance to be circulated round the engine and back into the turbo. NOT from turning it off without leaving it to idle for 5 minutes.

 

[Gambba]

Sorry Seizure some of my points were not made so clear due to over enthuastic typing, brought on by my half wit dealers stressing me out!

My meaning about the turbo and engine heating up when at idle is refering to after having driven the car, not from cold!

And reference the airflow, airflow across the engine is hardly worth talking about, I refer to airflow through the Rad.

Everything else I think is pretty resonable, although I still disagree with some of your points, but don't see the point in arguing about petty things. And I think that we can agree that after 'spirited driving' then a coll down is a good idea, but under normal controlled driving (Not that I know what this is) then there is no problem with switching off once stopped....agreed?

I only tend to leave my car idling for 1 min max after any sort of driving, but this is more to do with problems I had in the past regarding start up problems. The only reason i mentioned two minutes in my orignal post is because that's what I always say "Yeah hang on two minutes" yet 20 seconds later I'm done.....and plus I wasn't expecting any comments so didn't explain myself very well.