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Duramax 6600 Discussion Forum for the Duramax 6600 Diesel Engine, including the LB7, LLY, LBZ & LMM engine specific topics.

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  #1  
Old 03-29-2007, 02:37 PM
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Default Duramax coolant flow diagram?

Anyone have access to a good pictorial of the Duramax cooling system, showing thermostats, pump, radiator, etc and detailing coolant flow? If so, could you scan and post it - or email it to mark_rinker@hotmail.com?

Thanks in advance...
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2005 GMC Yukon Denali 6.0L gas (hey its paid for)
  • Previous owner of two 1994 6.5L K3500s, '01, '02, and '05 6.6L K2500s, '04 C4500, '06 K3500 dually, '06 K3500 SRW, '09 K3500HD SRW
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Old 03-29-2007, 10:36 PM
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Coolant travels from the water pump to the engine oil cooler, into the aluminum bellhousing adapter, into both cylinder banks at the back of the engine, then up into the heads, then to the thermostat housing.

Jim
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Old 03-31-2007, 07:09 AM
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Thanks for the description, JK.

You have mentioned in a past that one of the reasons for two thermostats is redundancy.

Are they 'serial' in their restriction of coolant flow, or 'parallel'?
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2005 GMC Yukon Denali 6.0L gas (hey its paid for)
  • Previous owner of two 1994 6.5L K3500s, '01, '02, and '05 6.6L K2500s, '04 C4500, '06 K3500 dually, '06 K3500 SRW, '09 K3500HD SRW
  • Total GM diesel miles to date : ~950K
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Old 03-31-2007, 08:29 AM
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parallel, and staggered by 5 degrees. One of them is a bypass stat. When it "opens" it closes off bypass flow.

If you squeeze your top hose, you will hear a rattling sound. This is the vapor purge mechanism "jiggly balls" in the rear stat.
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Old 03-31-2007, 12:11 PM
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Interesting. Is there a safegaurd to keep the two from being installed reversed?

My '01 pressurizes the cooling system, but only in cold weather (bypass mode?). Wondering what the effect of removing one or both thermostats would be and continuing to run this high mile engine for another 50K or so, and repowering in the fall before cold weather sets in, creating the coolant loss issue described in other threads.

Would you pull one, or both?
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2005 GMC Yukon Denali 6.0L gas (hey its paid for)
  • Previous owner of two 1994 6.5L K3500s, '01, '02, and '05 6.6L K2500s, '04 C4500, '06 K3500 dually, '06 K3500 SRW, '09 K3500HD SRW
  • Total GM diesel miles to date : ~950K

Last edited by Mark Rinker; 03-31-2007 at 12:23 PM.
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Old 03-31-2007, 01:10 PM
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The stats are physically different. Would be hard to install wrong....

Jim
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Old 03-31-2007, 04:34 PM
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Quote:
Originally Posted by Mark Rinker
Interesting. Is there a safegaurd to keep the two from being installed reversed?

My '01 pressurizes the cooling system, but only in cold weather (bypass mode?). Wondering what the effect of removing one or both thermostats would be and continuing to run this high mile engine for another 50K or so, and repowering in the fall before cold weather sets in, creating the coolant loss issue described in other threads.

Would you pull one, or both?
In theory, if you pull one or both, then the lower rad hose would be subject to suction collapse at high rpm.

The front stat cannot be installed in the rear, but I do believe the rear will fit the front housing. If that were to occur (wrong stat in the front) then the bypass would never be closed off, radiator flow would be reduced, and overheat would be the result on a workload session.

But I can't see how running without a stat can be less stressful to a high mileage vehicle.
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Old 04-01-2007, 06:56 AM
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Never had any overheat problems, even with the pressurization issues. Just bubbles in the coolant.

Thanks to both of you for your input.
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2005 GMC Yukon Denali 6.0L gas (hey its paid for)
  • Previous owner of two 1994 6.5L K3500s, '01, '02, and '05 6.6L K2500s, '04 C4500, '06 K3500 dually, '06 K3500 SRW, '09 K3500HD SRW
  • Total GM diesel miles to date : ~950K
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Old 04-01-2007, 07:20 AM
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Mark

I read your other thread. so I see what the context is now. Here is my take.

With gasket issues, the cylinder pressurizes the cooling system. Thermostat type, or lack of, should not have any impact on that. In reality, if you removed them, your truck would never warm up in colder weather, and would take an hour in warm weather. That is bad for the motor also.

That influence of migrating cylinder pressure stands to push out coolant, and the only way to stem that, is to reduce cylinder pressure. So if you have some highly advanced timing, it may help to retard it, but that is a band aid at best.

Solution:

You could go to a coolant with a high BP, like evans, and then drill out the cap, venting it to the atmosphere, that will give the excess gas a place to go, without pushing coolant out. In lieu of evans, you could use 90% EG, that would have little vapor pressure at normal loads and temps. You could probably use it as a daily driver for quite a while this way.

Basically, you are working WITH the problem, allowing it to purge.
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Michael 04.5 SRW LLY

custom stock intake, upsized boost tubes, Pre-turbo WMI, EFILive custom tune, Aerotech Scan Gauges.

Go Smokeless!
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  #10  
Old 04-01-2007, 10:43 AM
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Killerbee - nice article on the LLY overheating issues. I had one that ran hotter than my LB7s, but didn't overheat. Guess I got lucky!

I tried running the cap loose during cold weather pressurization and it puked it out the top of the resevoir instead of the overflow tube. At that time, the focus was on snowplowing and simply keeping the truck running.

I'll drill one cap and see what the results are. Thanks for the idea.

A nearly new '03 DMax engine will be delivered Tuesday. Maybe I can leave it on the shelf for awhile and save money for the labor of the swap. Its a shame to pull a perfectly good, smoke-free, non-oil using LB7 for a $10 gasket.
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2005 GMC Yukon Denali 6.0L gas (hey its paid for)
  • Previous owner of two 1994 6.5L K3500s, '01, '02, and '05 6.6L K2500s, '04 C4500, '06 K3500 dually, '06 K3500 SRW, '09 K3500HD SRW
  • Total GM diesel miles to date : ~950K

Last edited by Mark Rinker; 04-01-2007 at 11:02 AM.
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