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.
???

 

Check your radiator airflow, could have bugs or oil buildup on the engine side.........

 

What dsldan said.

Thermostat - several threads on here where that is discussed, some say 180[sup]o[/sup], others 190[sup]o[/sup]. I like the 190[sup]o[/sup] because it will make no difference what the temp will run in very hot weather, mountains, or pulling. If it is going to run at 200[sup]o[/sup] it will do so with either 'stat. However, in the winter time it will not open until 190[sup]o[/sup] thus keeping the temp warmer for the heater.

Normal - that's like talking about "normal" blood pressure. I have a 24v and I know that some run hotter than mine. Mine runs at about 180[sup]o[/sup] (I must have a 180[sup]o[/sup] 'stat) most of the time. The following is what my gauge looks like.

______|____+_ /
140 190 240

I consider that line (which is curved on the gauge) as being the "normal". When the air temp outside was 105[sup]o[/sup], and I was pulling my TT up a long steep hill my needle got over where I've put the "+" sign. I suspect around 220[sup]o[/sup] and since it is within that line I considered it "normal" and withing acceptable limits. I've heard that 230[sup]o[/sup] when climbing is OK.

"Sweeping" would seem to me more like a sending unit rather than thermostat, though I would replace the thermostat first as it is less $$$. Usually a thermostat will stick open or closed but not "sweep" like yours is doing.

Just my $0.000002 Stan

 

I run a 190* stat and it sweeps between 150-190 its normal...I have also hit mountain upgrades that will run my temp up to 230* while towing heavy...one upgrade that always gives me troubles is west bound on I40 in NC I need to stop and cool down about 3/4 of the way up this truck killer upgrade