You got a bad t-stat. Mine quit after I stuck a new one in, from Cummins no less.

My last post up there is the Technical Service Bulletin from Dodge, stating that the fluctuation is normal after installing the new thermostat.

ok i think everyone can deal with fluctuations in the temp guage but as the first post states 190 to 140degrees. i would definately not consider that "normal fluctuation" nor will i accept that as being normal.

mine keeps going to the line between 190 and 230 for about 2-3 minutes then goes back down to normal, using a IR temp gun the radiator is a tad over 170 when that happens

That's correct. it climbs to 190 and then hits rock bottom (the guage shows no temp at all) I mean it's almost as if the key was shut off to that one single guage. however it's just a couple minutes later, it'll start climbing again. It's leveled off now though. it seems to be acting like normal, and I never touched the thing.. I've about decided that there was a piece of trash causing the problem..

Has the coolant system ever been flushed??

i have my radiator completely blocked with cardboard for the winter

If you suspected a piece of something, I'd maybe take a look and see what is was?? :humm:

yeah, the motor was rebuilt 10000 miles ago, and all was flushed then.. I can't think of what else it may have been??

Maybe a piece of gasket material or RTV clogging the thermostat or temperature sensor? It's about time to do another flush on the system since you've already got 10k on the rebuild. I run Evans NPG Waterless Coolant. It's over $30 a gallon, but well worth it in my opinion. Especially for the hot Texas summers. A trucker friend of mine recommended it to me and he's got over 2 million miles on his truck. My girlfriend's dad has a small trucking company and his 3 trucks are now on Evans as well.