Hi guys, The temp. in my '96 seems to vary anywhere from 140 degrees to 190 degrees or more just cruising down the road. When I pull a long hill with a heavy load, the temp sometimes gets to around 220 and holds for a while and then drops like a rock to 140 or 150 again. I put a new radiator in about a month ago because the old one was plugged up solid and I was overheating all the time, this cured the overheating problem for the most part, and I thought it would also fix the eratic temp problem, but it still bounces around alot. I replaced the thermostat at the same time as the radiator. Didn't help so I replaced it again recently, thinking it might have been a bad one (napa), but still the same Any advice? Thanks!

 

The standard thermostat will cycle between 140 and 190. A replacement thermostat is available that reduces this but then it gives longer warm up times. Not a problem with it if you don't mind it cycling.

 

Cummins says,

THE COOLING SYSTEM USED ON THE CUMMINS DIESEL ENGINE EQUIPPED VEHICLES PROVIDES THE CAPACITY AND PROTECTION OF THE HIGHER GVWR AND GCWR RATINGS AVAILABLE ON THESE VEHICLES. OWNERS SHOULD BE ADVISED OF THE NORMAL SLOWER WARM UP AND LOWER ENGINE OPERATING TEMPERATURES ASSOCIATED WITH DIESEL ENGINES.

THE COOLANT TEMPERATURE GAUGE WILL FLUCTUATE ON DIESEL ENGINE EQUIPPED VEHICLES. IT IS INFLUENCED BY VEHICLE LOAD, OUTSIDE AMBIENT TEMPERATURE AND EXTENDED IDLE TIME. THIS FUNCTION IS CONSIDERED NORMAL

 

Wide fluctuations of the temperature gauge
the result of a large radiator, it is relatively harmless and normal
Cummins has released a revised T-stat that does fix the "problem". The revised T-stat Cummins part number is 3934373. (The old T-stat Cummins Part number is 3928499. )
This solution has been reported by Gerry Willomtzer <dax@yukon.net>: 195 degree t-stat Dodge PN 3418459 intended for a 1973 or so gas engine (From Gene's Chrysler in Fairbanks www.geneschrysler.com).
See this site: Wide fluctuations of the temperature gauge
the result of a large radiator, it is relatively harmless and normal
Cummins has released a revised T-stat that does fix the "problem". The revised T-stat Cummins part number is 3934373. (The old T-stat Cummins Part number is 3928499. )
This solution has been reported by Gerry Willomtzer <dax@yukon.net>: 195 degree t-stat Dodge PN 3418459 intended for a 1973 or so gas engine (From Gene's Chrysler in Fairbanks www.geneschrysler.com).

I installed this thermostat for the same reasons specified. "Fluctuations" from 160° to 190° this annoyed me. After installing the "corrective" thermostat it never went over 170° approx. I wound up putting the stock original back in. The replacement ran too cold.
For references see this site: http://dodgeram.org/tech/dsl/trouble...2v_trouble.htm

 

In my exp dont use anything but a Cummins thermo. And it seems every time I get a thermo from Napa for anything it cycles in a big way and end up removing it for another brand.

 

I put in the upddated one and it still fluctuates

 

HiD may debate that, I still can't believe what luck that was to have a new thermostat fail like it did on him.

 

My old thermostat would cycle the temp gauge a lot. A month ago it quit cycling. It would climb to just below 190° and then drop to slightly above the lowest "normal" range line and hold. Cab heat was very poor.
I got a replacement at Cummins (P/N 3928499) and now it climbs to midway betwen the low side and 190° and stays there. Cab heat good again.
Still going to replace coolant sensor on next maintenance cycle.

 

Thanks for the help, I guess if it isn't hurting anything I won't worry about it. It just seemed like all the temp fluctuation wouldn't be good for it, guess that's what I get for thinking . Thanks again for the help!