6.6 runs too cool

[kglenn]

05 is not reaching normal engine temp even in 70 degree weather. I have noticed in the morning the fan is cycling on and off when it is in the 30's. Sometimes it will come up, then go right back down. what to check first?

[Mark Rinker]

Coolant level
Overflow tank cap (replace)
Coolant sensor / gauage
Bubbles in overflow tank?
Coolant must come up to temp, there is nowhere else for the heat to go.
Are you reading the gauge only, or checking under the hood as well?

Erratic temp swings often indicate air in system, can be indicator of head gasket problems.

[drcook]

05 is not reaching normal engine temp even in 70 degree weather. I have noticed in the morning the fan is cycling on and off when it is in the 30's. Sometimes it will come up, then go right back down. what to check first?

first check the fan clutch. ours is being replaced monday morning under our extended warranty along with 2 injectors. our engine would never warm up, has gotten really bad lately, the cooler it is outside, the less the engine will warm.

this was posted over on one of the other duramax related sites. i went out and checked the resistance to turning of the fan while cold. checked it again after the engine ran a while, no difference (with the engine off of course, that is the lawyer avoiding disclaimer).

I put my scan tool on it and checked the actual temp while driving and with the temps in the high 50's low 60's the truck would run at 181 unless I was on the gas (figuratively speaking, this is a diesel of course so maybe we should call it the fuel pedal), then it would immediately drop back down

the other day, when the temp was in the high 20's here, the truck was running even colder, even on the expressway running 62 mph. finally I heard the fan cut out and the engine warmed up a bit more

with you noticing the fan cycling on and off, that is the first thing that I would check, especially since other people are starting to have the same issue, maybe it is just a time related thing, as our truck is an 04.5 but only has 55,000 on it

dc

[leolkfrm]

Have the t-stats been replaced? if so are they the proper type in the proper spot? do you use a front cover under 30 degrees?

[kglenn]

Checked the coolant level first thing this morning. Level was good. Grabbed the fan, it had tension for 2 revolutions then would free spin. Started the motor to let her warm up and it did not start cycling like it has been doing when I first start up in the morning. Came back out about four minuets later and it was cycling again. It has been running at round 185 degrees. Came up to temp the other day towing a trailer but once unhooked never came back up again. Think fan clutch?

[kglenn]

Oh, on the thermostat, I have not changed them since I purchased the truck. Has anyone had one of them to stick open and cause this?