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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > N54 Turbo Engine / Drivetrain / Exhaust Modifications - 335i > question about cooling off turbos



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      06-19-2007, 04:59 PM   #1
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question about cooling off turbos

Not sure if it is necessary and I am pretty sure bmw says it is not necessary..But I am just wondering what you guys think.

Occassionaly I will go out for a late night run where I drive my car alot harder than usual. In those instances when I come home I tend to let the car sit and idle for about a minute or so to let the turbos cool off.

Not sure if it is necessary or if it is either good or bad for the car. Some people have told me that I should thats why I do it. I only do it when I have been beating on the car.

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      06-19-2007, 05:00 PM   #2
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They have electric-powered water pumps for after the car is shut off. It's fine.
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      06-19-2007, 05:18 PM   #3
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I am not an expert, and don't know much about the BMW turbos, but after running, we would idle the cars to let the turbos slow down while the engine was on to keep them lubricated. When the engine shuts down, the oil pump shuts down and the turbos would be running without lubrication.

This of course was from years ago and I'm sure technology may have changed.
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      06-19-2007, 05:28 PM   #4
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Why would the turbos be running when the engine is shut down?
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      06-19-2007, 05:42 PM   #5
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Quote:
Originally Posted by rds95991 View Post
I am not an expert, and don't know much about the BMW turbos, but after running, we would idle the cars to let the turbos slow down while the engine was on to keep them lubricated. When the engine shuts down, the oil pump shuts down and the turbos would be running without lubrication.

This of course was from years ago and I'm sure technology may have changed.
The issue isn't lubrication, turbos have their own liquid bearings. The issue is cooling. The oil pump is shut off so no oil gets through to cool it down and that can cause them to stress and fracture. That's not true with BMW's turbos because they have an electric water pump that takes over when the car is shut off.
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      06-19-2007, 05:47 PM   #6
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The oil pump also runs too, a BMW tech on here confirmed that. so not only does the water continue cool the turbos the oil is still flowing for a short period you can hear them run if you really get the engine and turbos hot.
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      06-19-2007, 05:53 PM   #7
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you are supposed to drive around the block at 5mph to cool off the turbos with the driver side door slightly open. And then stay parked for another 10 mins before you can shut off the engine with the passenger side door open.
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      06-19-2007, 06:29 PM   #8
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I remember the

"Turbo Timer"- which would allow the car to run for a pre-determined amount of time after the key was removed and the car locked. The idea was to allow the turbos to continue to get the lubrication/or cooling the needed AFTER shutdown.
I believe coking was the problem- the small amount of oil left that was superheated.
Anyway, time and technology moves on. With electric pumps and such, it seems they have eliminated the need.
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      06-19-2007, 06:31 PM   #9
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Quote:
Originally Posted by urnuts View Post
I believe coking was the problem- the small amount of oil left that was superheated.
Anyway, time and technology moves on. With electric pumps and such, it seems they have eliminated the need.
Yes, coking is (was) the problem. With turbos that are oil AND water cooled, this is not a problem.
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      06-19-2007, 06:52 PM   #10
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We had a relative who had a 1986 944 Turbo, which pumped coolant to the turbo after the key was turned-off, that's 21 y.o. technology and not anything new....
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      06-19-2007, 07:44 PM   #11
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The coolant pump does run after the car is shut off if conditions warrant, however I assure you the oil pump does not. Its mechanically driven, not electric. And as others have said, the issue with cool down on old oil cooled-only turbos was oil coking, or basically boiling out of the bearing hoursing (CHRA) once the car was turned off and sludging in the CHRA and feed line which eventually leads to bearing contamination and/or oil starvation.
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      06-19-2007, 07:52 PM   #12
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the water cooling of turbos has nothing to do with the issue about keeping the car running on iddle for a while. U have to have an electric oil pump which keeps running independently after engine shutdown. If U shut down the engine with shinig turbos, the oill flow stops and has a potential to bake on hot bearings. Now a water pump which keeps running only helps to cool the turbos down faster, but does not prevent this oil-baking-to-bearings effect which happens a few seconds after the oil stops flowing (mech oil pump) and the turbo axle stops spinning. I also doubt an independent oil pump does prevent that for 100%. Think about it - is the oil able to flow inside the bearing with turbo axle not spinnig? Cuz it stops spinning after engine shutdown, right?
I admit the technology moved forward since I started to use turbos, but I'd rather keep it running for a while.

Another thing I got used to is keeping my right foot easy on the throttle s/t like 5-10 mins before the target - living in a block of flat I cant let the car run in front of the windows for lets say 5 mins with that exhaust... result - turbo cooled down before engine shutdown with no need to wait
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      06-19-2007, 10:22 PM   #13
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Quote:
Originally Posted by A418t81 View Post
The coolant pump does run after the car is shut off if conditions warrant, however I assure you the oil pump does not. Its mechanically driven, not electric. And as others have said, the issue with cool down on old oil cooled-only turbos was oil coking, or basically boiling out of the bearing hoursing (CHRA) once the car was turned off and sludging in the CHRA and feed line which eventually leads to bearing contamination and/or oil starvation.
I don't think I have ever heard the coolant pump run after shut off but I usually take it easy for the last 5 minutes before reaching my destination. Under what conditions does the coolant pump run after shut off?
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      06-19-2007, 10:35 PM   #14
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Quote:
Originally Posted by tjnptel1 View Post
you are supposed to drive around the block at 5mph to cool off the turbos with the driver side door slightly open. And then stay parked for another 10 mins before you can shut off the engine with the passenger side door open.
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      06-20-2007, 01:41 AM   #15
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Quote:
Originally Posted by A418t81 View Post
The coolant pump does run after the car is shut off if conditions warrant, however I assure you the oil pump does not....
Oh yea, tell that to the guy who tried to change his own oil only to have the oil pump spontaneously turn on after he removed the drain plug - spraying oil all over the place!

That's a pretty neat little trick for a mechanical pump.
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      06-20-2007, 02:15 AM   #16
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i have a question.

so is a turbo timer good for the 335i? if so is anything out yet? and you would recommend getting a turbo timer for the 335i?

thank you.
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      06-20-2007, 02:55 AM   #17
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Quote:
Originally Posted by Maestro View Post
The oil pump also runs too, a BMW tech on here confirmed that. so not only does the water continue cool the turbos the oil is still flowing for a short period you can hear them run if you really get the engine and turbos hot.

So basically with our 335i , we dont need to wait a couple (3-5mins) mins or to get a turbo-timer to cool off the car before turning it off then ?

I am quite curious about this questions, since in my city it gets pretty hot and especially after some serious driving ..

thanks guys
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      06-20-2007, 04:37 AM   #18
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Quote:
Originally Posted by twinpsi View Post
i have a question.

so is a turbo timer good for the 335i? if so is anything out yet? and you would recommend getting a turbo timer for the 335i?

thank you.
Read; it has a turbo cooler built in.

Quote:
Originally Posted by cool View Post
So basically with our 335i , we dont need to wait a couple (3-5mins) mins or to get a turbo-timer to cool off the car before turning it off then ?

I am quite curious about this questions, since in my city it gets pretty hot and especially after some serious driving ..

thanks guys
No. Just shut it off.
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      06-20-2007, 07:39 AM   #19
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Quote:
Originally Posted by tjnptel1
you are supposed to drive around the block at 5mph to cool off the turbos with the driver side door slightly open. And then stay parked for another 10 mins before you can shut off the engine with the passenger side door open.


I think you need to have the sunroof open as well for proper circulation. Possibly even the trunk....saw it in a tech update.
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      06-20-2007, 01:01 PM   #20
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Quote:
Originally Posted by wistarf View Post
Oh yea, tell that to the guy who tried to change his own oil only to have the oil pump spontaneously turn on after he removed the drain plug - spraying oil all over the place!

That's a pretty neat little trick for a mechanical pump.
Are you sure that the "spontaneously on" oil pump wasn't gravity I did some searching and there's no mention ANYWHERE of a electric oil pump which would be one of the worst ideas ever (besides the fact that I have never seen one, not even on dry sump systems). The only thing that shows up is on the 328, which has a "fully controlled oil pump" but is still mechanical.
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      06-20-2007, 01:15 PM   #21
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Quote:
Originally Posted by elucas730 View Post
Yes, coking is (was) the problem. With turbos that are oil AND water cooled, this is not a problem.
Is coking even a possibility with 100% synthetic oil?
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      06-20-2007, 01:53 PM   #22
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Synthetic oil is not magic potion, it still degrades like petroleum.

After a really hard run, eg at the track (not a drag strip), I will spray the oil cooler with a mist of water to instantly cool down the oil. I don't like 260-290 degree oil sitting on my engine components. Sorry, I'm old fashioned like that.

With misting, I've gotten oil temps to drop 20 degrees in a matter of minutes. Sublimation is a wonderful thing.
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