what does yalls engine tempeture usually run normal driving conditions? Mine seems to go all the way up to 195-197 then backs way down to 181-183 after a litle bit of driving time then usally steadys out between 186-190 sometimes going to 192-193 going up large grades on intersate. I have a edge atitude so i can see exact temps. But it seems to really fluctuate a lot just didn't know if all that was normal. And if it's not what it would be. This is on my 1999 cummins 5spd 4x4

 

Sounds perfectly normal. When the T-Stat open for the first time each day...it will climb past the normal temp.... open.... drop about 10* below normal.... then settle down. IF it starts to climb much higher before opening... your 190* t-stat may be getting old and sticking a bit.

I also have the direct readout from the Dodge computer (Adrenaline Pulse) and was initially surprised how much it jumped around.... compared to dash needle. But if you think about it... slight increases when working harder makes perfect sense. T-Stat reads highest coolant temps, directly after the coolant leaves the block.... heading to the radiator.

RJ

 

my 99 is doing the reverse....just barely on the line, tried cardboard, still the same....maybe t-sat locked open?...could it be anything else.

 

More than likely a stuck t-stat. Very easy change out.
Or can pull it out and see if open... and test it in some boiled water for smooth opening and closing.
If replacing...not a good spot to try and save $.
Go with only Cummins 190* t-stat. If interested... Cummins PN is 3946849

RJ