2001 RAM 1500 w/5.9 . Temp goes to 195 then drops to close to 160-170 and stays. I replaced the t-stat but get the same results.. Maybe the fan is not working correctly. I have cardboard in front of the radiator and fluid looks full.
Anything else I can try?

Thanks

 

Mine's the same way. I've replaced the thermostat 3 times and replaced the coolant temp sensor to no avail. Actually, mine never gets above about 160, even when it's 90* out.

 

Check the ground on your temp sensor, if it's broken loose or wiggling it will cause it to raise and lower.

 

Yeah, and the connector is really crappy on that thing if I remember right. The male plug on the sensor is all bendy and seems like it would break off easily.

 

Happend on my durango once, thats all it was.

 

where is the wire located??

 

The wire is in the harness that plugs into the sensor if I am correct.

HMMMMMMMM could this work the other way if the sensor is telling the engine that it's temp is cooler than it really is could this cause it to over heat? i.e. temp sensor says engine is 180 when it is really 200 and the engine will keep trying to warm it up and cause it to overheat?

 

check your rad cap

 

I dont see why it wouldnt, faulty wiring could cause a false reading.

 

All it would do is cause it to run slightly rich. The t-stat is mechanical so it will still open when it is supposed to.