I've got a '97 Cummins Ram 2500, stretch cab, long box, 4x4 with 3.5 rears, and an automatic. The thing runs fantastic, and pulls my boat and camper (each only 3000lbs.) great.

I noticed the engine temp guage "sweeping" from 150 to 190 constantly, and going almost to 230 on big hills (at 2500rpm with a bed full of gear, and a trailer). A friend has the same truck, and pulls an 8500lb camper up hills (with the air on) and never goes above 190.

I replaced the fan clutch, and that kept the needle between 180 and 195 until hill time - when it climbs to 220 or so. Does anyone know the recommended temp. range for the 12-valve Cummins? As I said, it runs great - I just don't want to damage a good running, expensive engine due to overheating.

I'm going replace the thermostat, but I don't know what temp. setting to buy.

I would think with a vehicle rated at 16,500lbs, pulling a 750lb box and a 3,000lb trailer wouldn't even make it breathe hard. ???

 

Mine is also a 97 2500...
On a 6% grade the needle will run up to about 205-210 something like that...and then stop! When the temp gets to that point I can hear a noise under the good that sounds like a jet plane taking off. Oh I forgot..we pull a 10k 5th wheel..

Rick

 

With the 97, the temp gauge sweeping from 150 to 190 and back is normal with the original thermostat because it is not breathing hard and has excess cooling capacity when the thermostat opens.

I also have a 97 automatic with 3.54 gears and tow an 11,000 lb fifth wheel. If you are attacking big hills at 2500 rpm, it sounds like the torque converter is unlocked, or you would be doing 65 mph in 3rd or 100 mph in OD. If the TC is unlocked, a tremendous amount of transmission heat is dumped in the engine mounted water cooled heat exchanger and causes the engine temperature to increase.

12,000 lbs on a 6 percent grade at 65 mph requires 210 wheel HP plus 20 HP for the fan. Your 97 was originally rated for 180 HP. If you have not done any bombing to the engine or transmission it wounds like you are full throttle and the tranny would be shifted into 3rd with the TC unlocked. Sounds like your rig is acting normal.

If you are driving up hills full throttle with the TC unlocked, slow down until you can keep the TC locked up. If you have bombed the engine and are experiencing TC unlocking, start checking out the tranny adjustments and electronics. Check out the DTT web site for discussions on tranny electrical problems.

http://www.dieseltrans.com/phpBB/index.php

You did not mention if your friend's truck is modified.

 

Sounds like you have a sticking thermostat, I had one that did about the same thing. Would cycle between 140 -up to 200-210, then drop suddenly back to 140. Sometimes it would be ok, then start cycling again. Got a new thermostat and no more problems. I think there was an issue with them from the factory, I remember back in 98' at the then called cummins 200 truck race, in Indianapolis, In. cummins held a truck show and was giving them out to anyone that needed them. Anyway they are not that expensive, and while your at it, don't forget about the belt, and radiator hoses, they probaly need attention.