Duramax Cooling System

Howdy, I haven't been here for a while.
I have a late '05 Sierra, Duramax 4x4.

Last weekend it was hot, 107+, and when I returned from an errand I noticed a coolant leak from the drivers side, but could not figure out where it was coming from?

The hoses are good and no residual coolant any where to be seen. The reservoir was low however.

On monday the weather went from hot to really nice, I dumped a gallon of anti-freeze in the reservoir and drove it up Cajon Pass, a pretty good pull, to see if it would leak again, no leak and the engine barely got up to normal temperature.

My guess is that one of the thermostats is stuck wide open, the last two days have been in the high 60's and it still does not seem to warm up to the 180-200 range.

Has any one else had this issue?

I would think your are right. My Duramax always comes ups to temperature even in the dead of winter. If yours won't, I'd bet your stat is stuck wide open . At least it didn't stick closed when it was 107*

John

Rog, sounds like the right diagnosis. My neighbor has an 05 GMC dually and his did the same thing a few weeks ago. The shop replaced it and no problem now.

Sounds about right, Hey John, what do you have hanging below your Landmark? I see a box, am I missinf something?

Thanks guys, there are two thermostats to figure out, of course...............

Howdy, I changed out the pump, it was leaking under pressure, and both thermostats, $800.
I think the thermostats were fine, springs were good and no corrosion.
The rig still runs lower than previously experienced, about 180D, instead of 190 or so.
The temp does go up after a hill climb amd seems to stay up then.
This fall weather, 50's in the AM and 90's in the PM, has been pretty mild this year.
Today should be 107+ again so I will give it a little test.
If it does OK I am not going to worry about it any more.
Here is a link to a Duramax forum that addresses the same question.

http://www.duramaxforum.com/forum/0.../45078-time-normal-operating-temperature.html

On edit:
The dealer wanted $1900 for the pump, and $250 for THE thermostat.
The service writer said it only had ONE thermostat!

Chainsaw said:

Sounds about right, Hey John, what do you have hanging below your Landmark? I see a box, am I missinf something?

Click to expand...

I fabricated a storage box and mounted one both sides. Worked out great.