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Duramax First Generation: 2001-2004 (LB7) Discuss the first generation (2001-2004 LB7) of the 6.6L Duramax diesel engine & associated components. Engine related discussion ONLY.

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Old 04-01-2019, 01:53 PM   #1 (permalink)
dandts
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Duramax 6.6 intermittent coolant problems

2002 6.6 Duramax Allison trans Chevy Silverado 4WD with 230K miles. New injectors and high pressure pump. The engine runs perfectly most of the time, some mornings after sitting all night I'll start the engine, after a very short time the engine overheat light will come on, the temperature gauge will fluctuate between 260 and cold, going back and forth, the check coolant temperature light will come on. Then the low coolant light will come on. The engine seems to run rough as if it's going into safety mode. This lasts for a couple of minutes then all the warning lights disappear, the temperature gauge stops fluctuating and it runs normal until I shut it off and it cools down for several hours, then it all happens again. The engine is ice cold when this happens, even when it's near 0 outside and the truck lives outside.

The coolant is full and I've changed the coolant temperature sensor near the gooseneck. The parts store said there were two temperature sensors and sold me two. I can't find the second one, I've looked everywhere that I can get at. Any Ideas ?

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2002 Chevy Silverado 2500 HD 4WD
6.6 Duramax 230000 miles
New high pressure injector pump and new injectors
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Old 04-02-2019, 07:57 AM   #2 (permalink)
Rvn4me
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Hook up a scanner and see if the temp. reading corresonds to what your temp guage is reading. If not then most likely the motor for the temp. guage in the cluster is bad.

Could be head gaskets
Combustion gas in the coolant system will usually make the temperature run really cool then really hot when working the truck. If your temperature gauge suddenly starts running colder than it always has, you may have a head gasket problem.

The quickest and easiest way to check for combustion pressure in the coolant system is to squeeze the upper radiator hose while the truck is running. (Please be careful and use common sense because the hose is hot) You should be able to nearly flatten the hose. If it is rock hard, like an inflated tire, your head gaskets are leaking. Some shops will do an actual pressure test to see what the coolant system is running at along with a testing of the coolant system to see if combustion gases are present.

I herd that a engine with 2 sensors came from the Southeast part of the country
One in back of each other
https://www.duramaxforum.com/forum/a...1&d=1329491765


Last edited by Rvn4me; 04-02-2019 at 08:24 AM.
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Old 03-04-2020, 09:50 AM   #3 (permalink)
dandts
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So, replaced and cleaned two engine grounds. Re seated all electrical plugs, problem solved.
There is one ground on the firewall on the right side, another on the lower front right side of the engine. Lots of rust isn’t kind to technology 😃
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2002 Chevy Silverado 2500 HD 4WD
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New high pressure injector pump and new injectors
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Old 03-04-2020, 03:32 PM   #4 (permalink)
davester
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thanks for coming back and posting what the fix was. That kind of electrical problem sucks to find.
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