Allowing the turbo to cool down - Advised?

[rdfcpete]

Guys,

Is there any need to allow the turbo to cool down on a Mk5 GTi, particularly when doing regular short'ish journeys that include up to motorway speed very soon into the travel but only for a minute or so?

I work just off of the A14 on a very short slip road and thus, I'm almost up to 60/70 within 40 seconds of being in the car. I always work up to speed gently avoiding high revs until the needle has reached midway, the regular idle temperature. I'm more concerned about my return journeys to work at lunch/commuting to work in the morning, i.e. turning the engine off very shortly after motorway speeds. This can be as little as 90 seconds or so.

When returning from driving at high speed, I know some vehicles it used to be advised (in the old days...) that you let the turbo cool down to avoid it blocking up. Is this a wise move with the Mk5's?

Thanks,
Pete.

[stealthwolf]

I've always disengaged the turbo when about a mile away from the house. That way, you get a head start on cooling down the turbo.

IIRC, it's not about blocking but about destroying it. If you're doing high revs and then stop the car and turn the engine off, the turbo is now spinning without lubrication going to it (someone please correct me on this), which leads to increased wear-tear and possibly damage.

[08micsta]

Hey

Its is extremely important that you allow the turbo a "cool down" period after any journey.

Turbo's can spin up to 80 000RPM (If not more) when they are in use. Now most turbo's share oil from the engine and are only lubricated whilst the engine is running... The constant flow of cooled oil whilst in use is what lubricates and keeps the turbo cool.

This is where we have an issue.

When you switch the GTI off (or any other car for that matter) the oil flow stops and your turbo goes into a phase called Heatsink.

This is where most of the damage is done. Shortly after turning the car off the turbo can reach temperatures of up to 200 degrees celsius. Because there is no flow of oil this means that the oil still in the turbo also reaches those temperatures. This can (Depending on the spec of the oil in your car) lead to graphite formation and the oil solidifying inside the turbo... (I think its graphite formation - Cant remember)

The next morning when you switch your car on the turbo breaks the solidified oil and imagine if you will; a rock scraping against Greenouses paint... Thats the effect you get.

So ideally about a mile from home you should ease of the accelerator, use less boost by keeping the RPM down and allow the turbo time to cool down.. That way when you switch off the effects of heatsoak are not as bad.

Im sure TT will be through to tear apart my explanation but that is as I have been taught in the oil industry how to deal with turbo's.

Mike

[Mark_GTIV]

Hi there,

While correct in general. The MK5 GTI has a protection mechanism which circulates coolent through the turbo after the engine has been switched off for a while. Your can read about it in the in the self study manual :

http://www.golfmkv.com/forums/golfgoodies/mk5golfengine.pdf

It states :

"To prevent carbon build-up on the turbine
shaft in the turbocharger, an auxiliary
coolant pump provides additional coolant
circulation for a certain time after the
engine is shut off hot."

So its good to run the last mile or two at an easy pace to let things cool off in general, including the brakes, coolent temp etc.. but the car also protects itself from 'normal users'.

[08micsta]

Perfect...

And Carbon.... Thats the one...Why did I think Graphite?

Mike

[stealthwolf]

isn't graphite just carbon in a particular form?
then again, diamonids are just another form of carbon too!

[Teutonic_Tamer]

Hey

Its is extremely important that you allow the turbo a "cool down" period after any journey.

Correct

Turbo's can spin up to 80 000RPM (If not more) when they are in use.

  You missed a leading one.  An average turbo speed on big truck turbos is around 160,000 rpms.  On smaller car sized turbos, particularly the K03, they can run upto 240,000 rpm! 

Now most turbo's share oil from the engine and are only lubricated whilst the engine is running... The constant flow of cooled oil whilst in use is what lubricates and keeps the turbo cool.

Spot on :afro:

This is where we have an issue.

When you switch the GTI off (or any other car for that matter) the oil flow stops and your turbo goes into a phase called Heatsink.

This is where most of the damage is done. Shortly after turning the car off the turbo can reach temperatures of up to 200 degrees celsius. Because there is no flow of oil this means that the oil still in the turbo also reaches those temperatures. This can (Depending on the spec of the oil in your car) lead to graphite formation and the oil solidifying inside the turbo... (I think its graphite formation - Cant remember)

Actually, you have the fundamentals correct, but most turbos can get upto around 350 to 450 degC.

And the oil turns to solid carbon, not to dis-similar to coal - which took the earth millions of years to form!

The next morning when you switch your car on the turbo breaks the solidified oil and imagine if you will; a rock scraping against Greenouses paint... Thats the effect you get.

Owch - that analogy sounds painfull - especially to Nathan!

But again, yes, fundamentally correct.  The hardened solidified 'chunks' will slowly wear away your bearing shells - which will then cause a lowering of oil pressure - not good!

So ideally about a mile from home you should ease of the accelerator, use less boost by keeping the RPM down and allow the turbo time to cool down.. That way when you switch off the effects of heatsoak are not as bad.

Spot on again.  Ideally, what you need to be doing is staying in 6th gear, with the least possible revs and throttle, but with a fairly decent roadspeed - so that there is a good airflow through the engine compartment, and the radiators.

Im sure TT will be through to tear apart my explanation but that is as I have been taught in the oil industry how to deal with turbo's.

No tearing apart needed 

[Teutonic_Tamer]

While correct in general. The MK5 GTI has a protection mechanism which circulates coolent through the turbo after the engine has been switched off for a while.

And . . . .

Your can read about it in the in the self study manual :

http://www.golfmkv.com/forums/golfgoodies/mk5golfengine.pdf

It states :

"To prevent carbon build-up on the turbine
shaft in the turbocharger, an auxiliary
coolant pump provides additional coolant
circulation for a certain time after the
engine is shut off hot."

I can 100% assure you that the after-run coolant pump will NOT provide satisfactory protection for the turbo!  Sure, it will circulate coolant around the turbo, but will do sod all for the oil - which will be sitting in the turbo bearings, merrilly cooking away, and trying to turn to carbon.

So its good to run the last mile or two at an easy pace to let things cool off in general, including the brakes, coolent temp etc.. but the car also protects itself from 'normal users'.

You are correct in running the last mile at an easy pace - but the after run coolant pump will not 'protect' the turbo.  Think of the after run coolant pump as something similar to say a lifejacket, or an airbag.  Both will help save your life, but it would be better not to crash the car or sink the ferry in the first place!