Holiday Rambler Endeavor

[1-waterman-1]

Well I am new to RVing, but not new to vehicle repairs, I have a 1996 Holiday Rambler DP with a cummins 5.9, When I purchased the RV the Temp gage did not work, I replaced the sender and the gage works now.
My problem is that when pulling a hill the temp gage rises to about the middle and then drops about 1/4 of the gage and then the process starts over until I go down hill. I have replaced the water pump, and thermostat, and cleaned the radiator.
It seams that when the engine warms up the thermostat opens and then closes, the thermostat should maintain heat in the engine, I have a dodge pu with a cummins and I don't have this problem with it.
Anyone have this problem ?

[BFlinn181]

Are you sure the sender is the correct one for the gauge? Also, the distance from engine to dashboard can be a factor, make sure all connectors are clean and firmly connected.

[Wdebarmore]

Maybe temps drop when cooling fan is kicking in.

[1-waterman-1]

I did get the correct sender, and it has a direct drive fan, It seams like the heater is not getting warm enough too, Thanks

[BFlinn181]

Even new thermostats can be faulty. You might pull it and watch it open in a pan of water on the stove.