Duramax coolant flow diagram?

[Mark Rinker]

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'?

[killerbee]

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.

[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?

[More Power]

The stats are physically different. Would be hard to install wrong....

Jim

[killerbee]

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.

[Mark Rinker]

Never had any overheat problems, even with the pressurization issues. Just bubbles in the coolant.

Thanks to both of you for your input.

[killerbee]

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.

[Mark Rinker]

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.

[redhot]

I am looking for a cooing system diagram as I do not like the way the truck
heats up.2005 year truck

[killerbee]

Your cooling system is not the issue.

Google "thermal feedback duramax lly"

A lot has happened since 2007.

[More Power]

To solve an LLY overheating problem, I recommend owners upgrade the fan, fan-clutch, fan shroud and radiator to that used by the 2006/7 LBZ. All of these OEM items are larger than that used on the LLY.

Jim