turbo cooling down

Hi,

is it true that turbo engines should be shut down right away but some times is needed to cool down the turbine by running at low RPM?

A.

Reply to
Andy Leszczynski
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Can you please point me to anyplace that suggests that turbo engines should be shut down "Righ taway"?

Turbines get very very hot -- if you come in your driveway after driving hard; the turbine will be hot.... it should be cooled donw a bit...

However, if you have an intercooler; they can probably shut down "sooner" vs letting them cool down for a few minutes...

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Reply to
Josh Assing

As a general rule turbo engines should be allowed to run for a short time if they have been working hard, to allow the turbo to cool a little and avoid cooking the bearings. Many modern turbos are water cooled, and don't need any cool down period.

Dave

Reply to
Coggo

Do you have any idea what an intercooler does, Dickhead?

Reply to
Holly Wood

I know with earthmoving equipment the turbo is usually slowed down first with the engine idling to allow it to get cooled and lubricated while coming to a standstill. I once had a four wheel drive with a turbo diesel which had an idling timer that could be preset for up to ten minutes so that you could lock and leave the vehicle with the engine running while the turbo slowed as the engine continued running. After the preset time, the engine was shut off. So in answer to your question I would say yes.

Reply to
Phil

Our experience with our '85 turbo Volvo supports that. It was my wife's car for a decade and I couldn't convince her not to race the engine when she started it in the morning. I winced when she pulled off the freeway into gas stations and shut down the engine right away - I could hear the turbo spin down after she shut the engine off. The 20 year old car has almost 240K miles on it now and the water cooled turbo is still hanging in there.

Mike

Reply to
Michael Pardee

Kinda sorta.

It's actually working on convection. The coolant in turbine housing will heat (and possibly steam), rising up toward the higher catch can. As it moves, "cooler" coolant will flow up behind it, keeping the turbine housing filled with coolant.

Reply to
CompUser

It's been a while since I've thought about it. The term I heard used to describe it is "thermal siphon".

Reply to
y_p_w

It's a combination of factors that made a cool-down period for (only) oil-cooled turbos important. If it's been run hard, the turbo housing is going to be hot (I've heard it can glow red) even though the oil cools the bearings. Then there's energy stored in the turbine. An immediate shut down would stop the oil flow, the heat from the turbo housing would transfer to the bearings without being cooled, and the energy from the turbo would create even more heat as it spun down. All this is happening in a small pool of oil that isn't going anywhere. The consequence was overheated bearings and "coking" of the oil that remained. A "cool-down" allows the turbo housing to cool and the turbine to slow down such that the heat sources before shut-down are severely reduced.

Adding water cooling doesn't slow down the turbine, doesn't cool down the turbo housing, and doesn't restore the flow of oil. However - it will draw the heat away that gets to the bearings from all these sources. I still allow for a small cool-down period, but I don't obsess over it. I actually back down an incline to my garage in neutral. The time it takes is from 20-

40 seconds.
Reply to
y_p_w

... except that the cooler air is flowing through the turbine, which is forcing the air into the engine. Since this heats the air, conservation of energy that states that that heat is drawn *from* the turbine. Heat doesn't appear out of nowhere. Thus, the intercooler does have a (probably mechanically insignificant) effect on cooling the turbine.

Reply to
k. ote

We're rapidly approaching the point of how many angels can dance on the head of a pin...;-)

A couple of points:

The air passing thru the intercooler is coming from the turbocharger *compressor*. The turbocharger turbine is on the other side of the house, handling exhaust gasses only. AFA as the IC having a cooling effect on the compressor, ordinarily it wouldn't, since it's downstream of the compressor's output. The only time the compressor would benefit from the IC's cooling effect would be during bypass valve operation.

Heat doesn't appear out of nowhere, it appears as a function of compression of the air passed by the compressor, according to the ideal gas law:

PV=nRT

With V (volume of the system), n (amount of gas IIRC) and R (a constant--Avogadro's Number? High school was a _long_ time ago!) remaining unchanged, if we boost pressure (P), the only "flex" on the other side of the equation is T, temperature.

Reply to
CompUser

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