how do you cool down a turbocharger?
July 22, 2011 10:15 AM   Subscribe

how do you cool down a turbocharger?

I recently purchased an Audi TT (1.8T) and subsequently began reading up on it online. it seems to me a complaint often heard is that people wreck the turbochargers simply because they don't know how to properly drive such a car. an explanation I have read more than once is that you are not supposed to go full throttle until the car has had a chance to warm up and that you are supposed to let it cool off before leaving the car parked for the night.

okay, letting engine and turbocharger warm up is obvious. but what do they mean by cooling it down? am I supposed to let the engine run in the parking lot after I have arrived or are they merely saying I shouldn't go 235km/h and then immediately switch it off? is mere inner-city driving sufficient to cool it down?
posted by krautland to Technology (14 answers total) 1 user marked this as a favorite
Basically, yes, don't push the car hard then immediately park it. The factory setup should be fine to cool the turbocharger. If you would like a little extra insurance, getting a turbo timer is what you would want to do.
posted by arrjay at 10:22 AM on July 22, 2011

...and I somehow hosed the link. Check out wikipedia for turbo timer.
posted by arrjay at 10:24 AM on July 22, 2011

I had a 99 A4 1.8t. Most of us who modded the cars (ECU chip) added aftermarket intercoolers and also used turbo timers. Realistcally if you don't drive it hard you shouldn't have to worry about hurting the turbo as long as you let it warm up to normal operating temp and then let it idle for a few minutes after driving a while to cool the oil down. Turbo timer is nice insurance though. Also an aftermarket oil cooler is a big help.
posted by white_devil at 10:38 AM on July 22, 2011

Also Quattroworld and VW Vortex have tons of info about 1.8t mods and maintenance.
posted by white_devil at 10:42 AM on July 22, 2011

When people say turbos get hot, they get HOT. It's not uncommon in some cars for the turbo to be glowing red after a hard run.

Since most turbos are oil cooled, once you turn off the engine, no more oil circulates through them. The residual heat attacks the oil and turns it into what's called "coke". I was under the impression that modern oils don't coke as easily as they used to.

Out of habit, and just because it's what my dad did when I was a kid, I always count to 60 after parking a turbocharged car before shutting it off.
posted by hwyengr at 10:52 AM on July 22, 2011 [2 favorites]

if you drive it hard just make sure you take it easy before you shut the motor off. you can also let it idle for a minute before cutting the motor off. turbo-timers help with this, but IMO your car is fine in factory form.

FWIW I make full throttle passes in my turbo cars and kill the motor at redline so I can read the spark plugs. I've never messed up a turbo doing this.
posted by mikesrex at 10:55 AM on July 22, 2011

I have a 1986 Saab 9000 turbo. Printed on the inside of the driver's side sun flap are stern instructions to let the car idle for 30 seconds every time before you turn it off, in order to allow the turbo bearing to cool.
posted by ErikaB at 11:16 AM on July 22, 2011

turbo technology has changed a lot since 1986
posted by mikesrex at 11:24 AM on July 22, 2011

Response by poster: thanks guys, that helps a lot.

I suppose there is some hard driving involved given that I spend roughly three hours per week on the autobahn (A7) but the rest is city driving.
posted by krautland at 12:11 PM on July 22, 2011

In all seriousness, don't worry about it. "Coking" (oil cooking and hardening on the turbo center bearing) used to be a problem with oil-cooled turbos in the 80s, but isn't a problem any more. Oil tech is better, bearing tech is better, and most turbos are water-cooled. Water cooling means convective movement of the coolant when the engine's not turning the water pump, which means the turbo is still getting cooled. Unless you're turning the engine off right after a dynamometer test (that is, full-power tests, in which case convective cooling wouldn't be sufficient over the lifetime of a car), it's not even worth a second thought.

Especially, especially don't listen to people on forums.

MeFi totally doesn't count
posted by TheNewWazoo at 12:40 PM on July 22, 2011 [2 favorites]

The main issue for the turbo on the 1.8t was oil starvation at the bearings caused by sludge, not coking as TheNewWazoo says. But many of us run track events and it is good practice to cool down your turbo after a heavy session. Also if the engine is off there is no water flowing and the stock intercooler wasn't that great at cooling even on the highway.
posted by white_devil at 1:37 PM on July 22, 2011

Since most turbos are oil cooled, once you turn off the engine, no more oil circulates through them.

The bearings are also fed with oil. Turbos rotate very, very fast indeed (several times the speed of your engine) and so not only will heat soak in the turbo be an issue if you drive hard and cut the engine off, but the turbo is spinning faster than you think for longer than you perhaps assume, so cutting of the oil flow to hot, spinning, bearings is not so helpful to their longevity. Localised hot spots on the bearings surfaces can royally screw their friction levels and reduced performance (the turbo won't spin quite as fast over time) and reduce the life of the bearings (heat damage produces friction, which produces heat, which causes heat damage, etc etc).

The oil fed bearings are also a great reason to make sure you are strict with oil changes, too.

FWIW I make full throttle passes in my turbo cars and kill the motor at redline so I can read the spark plugs. I've never messed up a turbo doing this.

You are, without question, shortening the life of your turbo considerably by doing this - just because you haven't seen the signs yet doesn't mean that you have magic self lubricating and cooling bearings. In addition, this gives precisely zero in additional information to spark plug colouration information. There is no gain but a decent down side to this practice - one minute of idling will not ruin the information from the spark plug unless your idle fuelling is for crap and it soaks the plug. If it is, run at full throttle and just overrun the engine with no braking for 30 seconds until it gets down to idle and then shut it off. At least that way the turbo will have got to manageable rpm before shutting it down. Injected cars put no fuel in at all on the over-run, so no 'colour loss' information is possible but it'll save your turbo life being shortened.

Besides, why would you 'read the spark plugs' when o2 sensors exist (and have for decades) and are enormously more informative? You can even install them and read them with a readout independent of the engine management system for a few bucks.
posted by Brockles at 8:19 PM on July 22, 2011

Oh, and:

is mere inner-city driving sufficient to cool it down?

Yes. High speed (rpm) and high load conditions produce the most turbo heat and are problematic. Normal putting around is perfectly fine.
posted by Brockles at 8:20 PM on July 22, 2011

As for fuel, I use widebands when tuning cars. But reading the plugs gives me peace of mind to know that my wideband is good.

I also read the spark plugs to check my ignition timing. I know there are other ways to determine if I'm running too little or too much timing, but IMO reading the plugs is still an important part of tuning a car. It's a common practice to put in a new plug or set of plugs in a car, make a full throttle pass and then kill the motor before redline to check the plugs. Once you start driving or let the motor run longer after the pass, the plugs will be harder to read.

And yeah, turbo technology has changed a lot since the 80's. Still, I would say to let the car run for a minute after running hard so the turbo can cool down some. And FYI whoever said something about the intercooler doing anything, that is just for cooling the air going into the motor. It doesn't cool the turbo...
posted by mikesrex at 8:28 PM on July 22, 2011

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