Engine/Transmission (1998.5 - 2002) Truck is overcooling, Please help.

[JCamper]

Well, I think the thing is, our trucks have pretty vast cooling capacities. Under normal towing conditions, I think they are cycling open and closed, but not necessarily ALL the way open. For instance, when it does this, the coolant temp will come up on a long steep grade, but then it will quickly drop back to the low mark on the gauge on the downhill side, and you can feel the difference in the heater. The radiator shop guy that I discussed this with said that sounds about right. The t-stat isn't necessarily snapping open and closed, so if it is staying pretty cool on the radiator side, when the t-stat opens, it doesn't open all the way. Just opens a bit, then closes a bit, kind of cycling between those 2 states. It would take a large hill or whatever to make the system hot enough to truly open it all the way. I had been doing some passing at 70+ with my camper on, and my parent's travel trailer behind me, up a significant grade, before mine did it. Right at 40psi and 1200 degrees for about a minute, minute and a half. Then on the way down the hill, noticed the temp drop drastically. My water is still full, looks good, no other changes in power, etc. Jcamper

 

[ScottyG]

Jc,



My truck is behaving EXACTLY like yours was/is. For the first 1 1/2 hr of towing, everything is normal. You can tell the t-stat is cycling normally. During this towing time, there are some hills and mostly all the towing is towing my GearBox (12k loaded) at 70-75mph. On some of the hills, I'm at 1200egt and 29psi boost. I KNOW I am making heat in the engine. Of the 2 t-stats I have changed, they both came from the Cummins shop. The radiator was removed and flushed last summer.



I have been towing my tractor around during the last couple of weekends and everything is fine. They are only short trips and only 9000lbs. The problem only happens towing the camper after about 2 hrs into the trip. It happened in mid summer at 95* towing in the hills.



On the last trip(2hrs), I got to the camp site and unhooked. The engine was at full cold by then. We went back into town for dinner and I checked the engine in the parking lot of the resturant. It was full cold. Checked with the lazer and it read 126*. :--) It was also cold to the touch. It was about a 7 mile drive from the camp site to the resturant. After dinner, on the drive back to the site, it warmed up and functioned normally. The next day after the race, on the way home, it warmed up normally. The first 1 1/2hr of the ride home, it was right at 190*. Then it started dropping slowly again. By the time I pulled into my driveway, it was at 140*. During the week, everything is totally normal. This is killing me. Where is the heat going?



Scott

 

[chef]

Is it possible for the auto transmission to do the same thing? I just got the truck and installed a temp gauge, first time towing and it stayed around 120. If i'm driving around town it'll go to about 150, but on the freeway that night with about 7-8k behind me it stayed really cool. same thing the next day too. just curious. I'll probably need to pick up a thermometer like that too, if nothing else I'll end up using it for my nitro car.

 

[Royal]

Scotty---You stated that at 190 temps your fan cycles normally and you can hear it. The fan should not cycle at 190. It normally starts to cycle about 210.