running Hot or not?

I have a 04 dodge 3500 with 5.9 diesel with a automatic trans. Noticed today as I was traveling through some hilly roads pulling along about 12,000 pounds behind me the temp gauge rose quickly after the trans dropped out of overdrive/lock up.. It went to the top end of the scale but then as I crested the hills and the trans shifted the engine temp gauge dropped back down to normal within a mile. Never did this before so I checked the radiator , oil and trans fluid. All were they should be. Now what could cause this to happen.

Time to have the radiator boiled.

I don't know if that would be it. The antifreeze has been changed out twice, both time when the water pump was replaced. I will check into that . A friend of mine thought maybe the turbo might be going bad. I don't know how to check that. The engine runs fine , gets good fuel milage, both towing and normal daily driving. How would the turbo be checked?

it is possible the lock up may not be working--which means the torque converter will be heating up---most guys can tell when the OD goes on and off but the lockup function is so slight most cant tell if it actuates---on the tach it will show a 300 rpm drop when it locks up....

The lock up is working, when it up shifts as you say the lock up acts like another gear.

Check the rad with a temp gun and see if you can find hot and cold spots. I know a decade of hard work usually means my diesels needed a thorough cleaning to cut down on temp rise like you are seeing.

Will do, I do have a laser temp gun that I use to check wheel bearing temps on the trailers.

Also look for bug build up and bent fibs on the condensor, coolers, etc

After a WOT blast, I can watch my gauge go from 195-ish to 215-ish but the right back down. I'd say working hard up a hill, I would expect to see some temp rise. Not sure if be comfortable if it pegged though.

Sounds like air in the cooling system to me. Should use a vacuum filler to be sure to get all the air out with today's cooling systems with very small openings in the radiator and heater core, easy to have air trapped in those during refills and cause those problems.

I used to fight that problem until I started using one.

I have never heard of a vacuum filler, I 'll google it .

This is the one I use.

I had trouble getting coolant to flow through heater cores and making heat for the cab after changing coolant. This solved that and is a must on some vehicles now a days.
Link

I did a Google search, watched a you tube video, looks like a procedure that should be done each time there is a coolant change. Thanks for the info.

Happy to help, hope you get it figured out soon enough.

Air in the system causes problems when the engine is working hard and so then is the cooling system...it can't handle air in it to work smoothly and reliably. Sometimes no matter how hard you drive it/rev it that air ain't coming out without a vacuum.

Joe dirt voice... "don't ask me why, it just does"

Where is your row of pyro gauges? Didn't you know that ALL diesel owners should have them in the cab, or at minimum an Edge box with Attitude to make sure you are always in the parameters of proper function...