I recently took my 97' to my local dealer to have the transmission serviced and have a look at why my temp gauge that wasn't working. In the process they changed the thermostat because they said it wasn't warming up to temp. I still ended up buying a new sending unit. Now that the gauge works the temp comes up to 180 like it should and then falls rapidly down to 150 or so and the slowly back to 180. My dealer checked it again and said that was normal. Has anyone heard of this happening? Also, would it hurt to put a 190 thermostat in it?

 

It is normal for the temps to rise and fall like that.
It is a sign that your t-stat is working.

Some folks dont like a t-stat that is always opening and closing so they change to a different t-stat.

Someone here may even chime in with the part number for the different t-stat.

Rich.

 

Some of the after market guages I have installed in different vehicles scared me when you watched them cycle up and down until until it stabilized. Its really the rush of cooler antifreeze hitting the sender. It seems stock type guages are a little more buffered in swings. from other postings if im correct, the 180 is to low unless you live in a hot area and run it hard always, the 190 would probably be a better choice.
Just my pennies worth.
Apache.

 

My truck does the same thing. Cummins came out with an updated t-stat that is supposed to stop this from happening. I bought one and put it in and it still does the same thing. I checked the part numbers and I know I got the new one. Maybe one of these days I will try again. I have heard that the cycling is bad for these motors and I have heard that it is not. I have 155,000 on mine and it is doing just fine so I am going to leave it alone. Hope this helps.
Justin

 

My truck also does the same thing and so does my buddy's 94 and he has over 200,000 and no problem. Don't worry. Just drive it and enjoy. Maccandy 8)

 

I also thought that the "normal or stock" thermostat is a 190. It does do the swing thing (mine does too) and is considered normal.

The newer style thermostat is designed to eliminate the swing thing, but people who have switched to it report that it takes longer to warm up. Something to consider if living in a cold climate.

Ditto on the 180 thermostat, it's only for warm weather climates. Kevin

 

It is/was normal for the water temp to fluctuate, but Cummins did come out with an improved thermostat. The P/N I have for the thermostat is 3928499; gasket is 3927305; seal is 3925466. Having said that, I make a habit of contacting my nearby Cummins shop to verify correct P/Ns for my engine by serial number. I always have the engine serial number and CPL number ready when I'm talking with the Cummins people.

 

Mine rises to 180 or 190 pulling then drops to 150. Ive been told it was normal so i pay no attention unless it get higher

 

My 96 ''cycled '' like that ..service manager made a point to mention it the day i bought the truck..then after a few years my stat stuck and had to be replaced..by then the new version was out and no more cycling