[urq] turbo idle down

[Jon Archibald]

Hi Johann,

Your turbo generates heat from the compression process. The "Idling down" is
essentially circulating oil and/or coolant through the turbo's bearing
housing under non-boost circumstances (idling OR just easy driving where the
turbo spins bust doesn't make boost). This cools the turbo but also keeps
the oil moving so it doesn't just sit in the same hot spot and "coke" in
your turbo bearings. The afterrun (or "aux.") coolant pump is a good safety
feature for folks who don't understand this or don't have time to think
about it, because it cools the turbo for a few minutes after the car is
turned off. It's not as good as a "running" cool down, though, because it
won't also keep the oil moving. 

 

I don't run an afterrun pump to my Rs2 turbo; I just make sure to take the
last mile or 2 super easy (no boost), which I think is the best way. More
airflow to cool the liquids and surface of the turbo and more movement of
the liquids due to 3-4k rpms driving the oil and water pumps instead of the
<1k rpms of the idle. If I can't do that I just idle for about 2 minutes
before shutting down.

 

You can tell if your afterrun pump is working by carefully putting your hand
on it after you turn the car off. You'll feel a gentle vibration if it is
working. It generally runs off a thermostat so will probably only turn on if
you gotten the car nice and warm. Take a good look at your hoses and make
sure no P.O. has bypassed the afterrun pump. People do a lot because they
tend to leak when the plastic pump housing gets old. If it's been bypassed,
it's for a reason and prob. needs to be replaced. Again, if you "manually"
cool down after hard driving as described above you don't need it anyway.

 

As an additional safety factor, I run fully synthetic oil in my turbo
engines because I believe it has a higher threshold against thermal
breakdown and thus will "coke" less inside hot turbo housings.

 

Good luck!

-Jon