Oil temps in liquid cooled turbo engines

[Nederlander75]

I am pondering this for 2 reasons. 1st is in regard to idiling down the turbo beyond 60 seconds under normal driving. 2nd has to do with one of the things I see here a lot where people recommend higher viscocity in a turbo application.

1st, given that the turbo is liquid cooled on top of oil circulation wouldnt it be safe to say idiling it down to cool it would be no more necessary than idiling down a naturally aspirated engine? Youd be getting high temp deposits/coaking regardless.

2md, if the oil is not being subjected to temps it would under non water cooled applications why the higher viscocity to protect the high temp areas of the turbo? Same logic as above, if this is necessary under a liquid cooled turbo applications where the oil temps average the same as the coolant then why not for naturally aspirated ones? Is this because of the temps in the turbo, while heat is being mitagated, is still higher than the hottest seen in the rest of the engine?

What, if anything, am I missing?

Thanks all

 

[aquariuscsm]

I never idled down my old 300ZX turbo at all. As soon as I arrived at my destitation,I always immedately shut down the engine. Car gave me zero problems whatsoever,and I always drove it like I stole it :^)

 

[XS650]

The goal isn't to get overall oil temperatures down, it's to get the turbo cooled down enough that it's heat soak doesn't coke the oil. If you drive like a sane person for a few blocks before you shut down, then it's fine.

If you come blasting in off a hard run and shut down immediately, then you are asking for trouble.

 

[Doug Hillary]

Hi,
XS650 - IMO your comments are on the money

Turbo charger positioning is important as it the rotational speeds attained. Many early turbo charger installations were inherently wrong in their location and in the way lubricant was supplied and emptied from the cartridge. Many early installations were effectively "bolt on" and in some cases very high oil temperatures were experienced as a result (Porsche 924 as an example)

In heavy trucks where the bulk oil temperature is often around 100-110C it is common now (has been for a decade or two) to instruct Drivers to simply drive to the point of stopping at low revs (a minute or two) and shut down immediately. If stopping after climbing a long hill then it's best to wait until the pyrometer (or coolant) has stabilised at around "normal" - a minute or three perhaps. In some cases it may take up to 30secs or so for the impeller to stop turning

Better metallurgy, bearing design and placement and modern lubricants have certainly stopped many of the percieved "problems" with turbochargers on any account

My advice (and my instructions to my Drivers) is as above - I have never experienced a turbocharger failure (not thru shutdown - only on warranty) in many many millions of kms!

 

[BuickGN]

I think the higher oil temps come more from the power density, not the turbo itself.

Until recently I've always run a non water cooled turbo and have never had a failure due to hot shutoff. I drive it nicely a couple miles before I shut it down and it's fine.\

Water cooled or not, oil temps will be roughly the same.

 

[Nederlander75]

Thank you guys. What does this mean for higher viscocity in turbos?

 

[mechtech2]

ditto XS650