Hi all this will be my first post. I finally got me a 96 2500 Cummins and while driving it home about a 45 mile trip I noticed the Temp gauge warmed to about 150/160 degrees then when I looked again I saw that it was at 190 degrees.....while watching it all of a sudden the needle went from 190 degrees down to about 160 degrees then back to 190 degrees and so on back and force pretty much all the way home, but never went above 190 degrees. These fluctuation I would have thought to be normal from the thermostat opening and closing, but the movement were pretty quick back and forth. Do any of you experienced Cummins people have any ideas?? Please Help. My direct Email if you would rather PM me is (ingramg@yahoo.com) Gene

 

I would change the thermostat. get the thermostat from Cummins, and I bet your problems will be solved.

Heres a quick and dirty how-to:

http://dodgeram.info/tsb/1994/07-07-94.htm

 

Would a bad thermostat cause such quick temp changes?

 

That is normal. It alarmed me as well when I first noticed it. You are correct that it is the thermostat opening. What happens is that when your thermostat is closed, the coolant in the radiator cools off a lot but the stuff in the engine is getting warmer. When the thermostat opens, the temp sensor sees all the cold coolant from the radiator and plummets.

The two ways to get rid of the fluctuation are to keep the coolant in the radiator from cooling off so fast or to work the engine harder so that the thermostat stays open more of the time. Working the engine harder is not a good option unless it just so happens that you need to tow something. Keeping the radiator warmer can be done with a winter front or a piece of cardboard.

 

Dartmouth when you noticed this kind of Temp change on your truck did you have the quick swings from like say mine 160 to 190 to 160 back and forth? I am familiar with the way cars Temp changes occur when the Thermostat opens and closes but those changes do not happen very quickly back and forth like this truck is doing. It just makes me a little worried.

 

I have not personally seen that in my 12V.

 

That's because you have a '98.
In '98 Cummins moved the temp sensor because of complaints about the totally normal temp swings.
The coolant temp in your '98 still swings, you just don't see it.

Don't worry about the swings in a pre '98, they are normal and you'll just make things worse trying to fight it.

 

Infidel to the rescue again...lol

Thanks for the insite !

 

Perfectly normal behavior for these 2d generation dodges. When I first got my 96 it did the same thing and I posted here just like you did.

 

My 95 has the same temp swings, and I added grill covers and it has no noticable difference

 

Look in your owners manual, it actually explains that it is normal due to the heavy duty cooing system.

 

What it 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.

Back when our 12 valves were being sold new the salesmen where instructed to inform buyers that the fluctuation was normal before the truck left the lot.

 

Wheww thanks guys this is good news and puts the mind at ease. On another note I also noticed something weird with the Auto transmission but I need to double check that before I post that in another post. Thanks again.