Hawkeye D

WRX STi Spec D 07/07

I noticed yesterday a pipe going from the top of the expansion tank into a metal pipe which then goes into what looks like the middle of the turbo.

Is this simply water that gets pumped around the bearings whilst driving?

Also, does this cooling play any role once the engine is switched off?

merlin24

iTrader: (1)

The central housing of the turbo is water cooled and the oil feed is for lubrication and also helps cool the shaft and bearings.
If you think that the turbo spins at approx. 20,000rpm on tickover and anything up to 200,000 rpm on full chat, you can see why it needs all the cooling possible.
With the engine off after a run, the coolant also helps to dissapate the heat from the CHRA (central housing rotating assembly) as everything cools down.

Mick

GC8

My 944 Turbo has a small electric water pump which keeps coolant circulating through the turbo for a minute after the ignition is turned off.

I havent seen this on any other cars, but itd make a very useful tweek.

Hawkeye D

Thanks Mick. So is there another pipe coming out the other side of the CHRA?

merlin24

iTrader: (1)

Yep - coolant feed off the back of the R/H cylinder head via a banjo bolt and the other one you have noticed to the header tank.

Mick

Hawkeye D

I'll have a look at this, it completes the loop / circulation. That's where I was lost.

Jacko4130

iTrader: (3)

My 8L Audi S3 had a after run pump for the turbo, Ran for a few minutes.