goes all the way back down to 140-150*. This is almost systemic. Is it normal?

 

thermostat bad?

 

So it isn't normal for it to cycle like that?

 

Competely normal. But if it bothers you , you can replace the Thermostat for another one.

My last 3 12-Valves all did the same thing.


From dodgeram.org...

"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. ) "

 

i never heard of that good to know

 

I figured it was normal, but at the same time I got thinking.. diesels dont like to be ran terribly cool. I wonder if it running so cool could have something to do with my dismal mileage?
I might pick up that new t stat though since cummins decided it's revised and must be better

 

I wouldn't worry about it until you're ready for a coolant change. It's a common sight on these trucks to watch the gauge move up & down, but it's not a "problem" or really even a concern and it won't affect how your truck runs. I've heard of people putting in the revised Thermostat and the gauge still moves back & forth. Mine have all been stock and I've never seen any of them reach over 190*, even in 100*+ Texas summer heat.

 

I dont doubt the temp will ever go higher than what it does now, since these trucks have amazing cooling systems. But I wonder how that swaying affects mileage? Running a diesel too cool will hurt mileage so I'm curious to know if it impacts it.

 

mine does the fluctuations sometimes and other times it doesnt I know its the thermostat opening and closing but I guess its normal

 

mine does it althe time when im going 70 + down the highway, its just the tstat opening and exchanging hot coolent for cooler coolent in the enging, nothing to serious, a new tstat might help if your worried