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Was reading on another site that the coolant flow through the turbo on an LB7 was thermostatically controlled and once the engine reached operating temperature, the flow through the turbo stopped. This is according to SAE paper 2001-01-2703, which I cannot find of course. So with coolant not flowing through the turbo at operating temps, is there still that much convection going on cooling the turbo if there is no flow??


Thoughts??
 

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4x4man said:
Was reading on another site that the coolant flow through the turbo on an LB7 was thermostatically controlled and once the engine reached operating temperature, the flow through the turbo stopped. This is according to SAE paper 2001-01-2703, which I cannot find of course. So with coolant not flowing through the turbo at operating temps, is there still that much convection going on cooling the turbo if there is no flow??


Thoughts??
Yes there is a thermostat valve but I think it's to control flow when the engine is cold. Opens up after the coolant gets warm. So you have full flow at operating temps.
 

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Discussion Starter #3
Hoot-


Thanks for the reply. I was thinking the same thing, but I am not sure at this point which way it is. Here is a direct quote from the article:


"As a point of interest, we know that the LB7's turbocharger employed a water-cooled center section, and we know that the new Garrett variable nozzle turbo does not. Most of us thought a water-cooled turbo would improve durability, but SAE paper 2001-01-2703 indicates that coolant flow through the LB7's turbo was thermostatically controlled, with flow stopping once the engine reached operating temperature - designed primarily to quicken engine warm-up."


Source: http://www.thedieselpage.com/duramax/lly2004.htm
 

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Actually if you think about it, to speed engine warmup, coolant flow typically is supressed. That's what I thought the valve does when the engine is cold, supresses flow to the turbo until the engine warms up. SI 2000 service manual states that a bad turbo coolant control valve could be the cause of engine not getting up to temp.

Would be pretty stupid to suppress coolant flow to the turbo when it's hot.

Now ..... it is possible that is the way they designed it, pulling heat from the exhaust, but I'm not so sure.

I'm going to dig into this one.


Edited by: hoot
 

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Cooling Cycle (6.6L Diesel Engine)

Coolant is drawn from the radiator outlet and into the water pump inlet by the water pump. The coolant flows to the heater core while the engine is running. This provides the passenger compartment with heat and defrost.

Coolant is then pumped through the water pump outlet and through the coolant pipe to the engine oil cooler. The coolant flows around the oil cooler element and to the rear engine cover. The rear engine cover distributes the coolant flow to both banks of the engine block. In the engine block, the coolant circulates through the water jackets surrounding the cylinders where it absorbs heat.

The coolant is then forced through the cylinder head gasket openings and into the cylinder heads. In the cylinder heads, the coolant flows through the water jackets surrounding the combustion chambers and valve seats, where it absorbs additional heat.

Coolant is also directed to the turbocharger. There it circulates through passages in the center housing. <font color="magenta">During engine warm-up cycle the bypass valve located in the turbocharger inlet hose at the outlet pipe prevents coolant flow. During normal operating temperatures, the coolant assists in keeping the turbocharger cool.</font>

From the cylinder heads, the coolant flows to the thermostats. The coolant flows from the thermostat housing to the water pump through the bypass pipe until the enginereaches 85°C (185°F).

Operation of the cooling system requires proper functioning of all cooling system components. The cooling system consists of the following components


From GM SI 2000Edited by: hoot
 

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Mackin said:
So Hoot are you saying the above "linked" article is incorrect ?


Mac
No I'm not...

The GM service manual says that article is incorrect though.

Personally I found it hard to beleive there is no coolant flow to the turbo when the engine is piping hot. How could they have called it a water cooled turbo after all this time?

It does sound like a good idea to pull heat from the quickly heated exhaust side of the turbo by using the cooling system. But then you wouldn't need the valve at all. Think about it... with full time circulation you would be pulling heat from the turbo and helping heat the engine. Then at higher temps, the radiator would come into play, keeping temps down. Logic tells me the engineers decided to install a thermostatically controlled valve to suppress circulation when the engine was cold because the area where the coolant encircles the turbo does not generate enough heat early on.

Edited by: hoot
 
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