Truck at dealership for overheating

[Jared Herzog]

Just checked mine. It has resistance. I can move it by hand some but it does not spin at all.

 

[TCornish]

I told them about that when I called to get a status. I am thinking of picking up the truck and test driving it myself on the way to another dealership in the morning. At least there are more than one diesel techs at the dealership I will be heading toward.

 

[p-Bar]

Wouldn't they pressurize the cooling system and monitor it?

 

[Jared Herzog]

I think you are on the right track with the fan clutch. I have seen them locked up where they roared the whole time. I have also seen them where they do not engage and just basically free spin and when the motor is turning rpm and you are driving in traffic at slow speeds the fan is not catching and keeping up. Hope the next dealer gets you fixed up. Good luck.

 

[AH64ID]

It sounds like a sticking thermostat for a couple of reasons.

The fan clutch and fan rpms are ECM monitored and should throw a code if your fan isn't engaging and speeding up properly. The dealerships first step is to check for codes. It doesn't take long to set a code and with the warm temps you've been having the ECM will be using the fan for a/c and would have thrown a code.

If you're just driving around on a 94° day without a load, uphill, at high speed there just isn't enough heat being produced by the engine to heat the motor and radiator to 215°. It takes a lot of work being done to get to those temps.

With a 190° thermostat the fan doesn't even really begin to kick on until around 210°, which means it's never really used 90% of the time. Last summer driving around in 120°+ weather my fan wouldn't ever cycle from coolant temp and only from a/c operation and I have my fan programmed to come on sooner than OEM programming. Even in 120° weather my coolant temps were only a degree or so higher than a 80° day if I wasn't loaded or towing. Going up a 6% grade at 75 mph and 114° without a trailer I only got to 204° and the fan never cycled. I realize the cooling systems on my 5.9 and your 6.7 are slightly different but I just pointing out how much heat it takes to get the block and radiator to 215°.

The 190° thermostat cracks at 190°±3° but isn't fully open until 207°. Unless you're always towing the thermostat rarely goes full open so they develop wear spots on the shaft. Those wear spots can cause the thermostat to occasionally bind. My OEM thermostat was binding pretty bad at 55K miles and it was replaced. It can be noticed by slightly higher temps for the initial opening such as 197-202° vs 191-194°. When towing it will also get to 207-210 faster.

The fact that it happened once and hasn't happened again is another indication it's the thermostat.

How many miles on the thermostat?

FYI oil temp is a fake number.

 

[TCornish]

I think you are on the right track. I drove it home yesterday, 50 miles through slow traffic at first, then highway. The temp on the coolant went up to 197 before dropping to 190. The transmission never got above 168 and the oil 199. I even drove it again and tried aggressive driving. I will order a new thermostat and be done with it. They checked the fan clutch as I asked and said it was fine. They charged me zero dollars which was very kind.