Got the temp up a little over 200-210* last night coming out of Palm Springs. 20 miles later, it dropped down to about 180*, as usual.

Then it kept dropping. sits between the 140 mark and the next mark and don't move any higher.

When I got home last night, I check the radiator. No pressure when I took the cap off, and I could stick my finger in the coolant for a few seconds before it got uncomfortable. Radiator is full and I didn't see any coolant leaks.

Sound to y'all like the t-stat is stuck open?

 

That would be my thoughts, besides the way it got hot I would definately put a stat in it. just my .002



good luck

 

Quite common for the rubber seal around the stat to come off and hold it open. I just remove the seal and toss it, use the stat without it. Doesn't seem to make any difference.

 

Samething happened to mine after a dyno run. Wish I had seen this thread before I spent $30 on a new Cummins T-stat. Oh, well now I've got a spare.

 

Bypass was stuck open.....

Ended up wuth the wrong t-stat, so I didn't change it. The old one worked fine this morning on the way in to work.....

 

I've changed t-stats twice, and I still can't get my truck over 150 degrees except for a few degrees after running up a long hill. I freeze my stinkin' b$@#'s off every winter. In cold weather, I cover the entire radiator with cardboard and the temp still sits at about 150. I even had my dealer take my t-stat out and check it, and it worked fine. It's great now in the summer, I have no worries of over heating. However, winter is coming up and I don't want to have to build a campfire in the floor to keep warm. Any ideas?

 

I totally remove my fan from Oct till June and run grill inserts. Heater works great then, engine is much quieter, you never would guess how much noise the fan makes even when not locked up. Truck also seems snapper on takeoff.
I've run without the fan up until outside temps get up to the 80°s with no problem but you might not want to run the A/C in stop and go traffic. Most all of my CTD driving friends in Montana do this. Once you get it down the fan can go off and on in just a couple minutes. Nothing else needs to be removed to pull it out, it will fit out the top.
Big problem with going fanless is I hate putting it back on, engine is so much louder.

Another trick for a faster heater is to use the recirc position on your climate control, the one with the picture of a truck cab with an arrow though it. I've had my heater running in recirc, switched over to a position that sucks outside air and watched the engine temp gauge bottom out almost instantly when the outside temp is below zero. These diesel engines run so cool that I'll bet you could get by without a radiator most of the year, the heater core would be enough.

Don't use defrost when the engine is cold if you can avoid it, it runs the A/C and just makes you colder. You can pull the relay for the A/C or easily modify the switch so you're the one in control of the A/C.
Instructions here>
http://dodgeram.org/tech/repair/HVAC/Defrost_AC.htm