temp gauge fluctuation

[markm]

I tow a 29ft 5er that weighs about 9500lbs when loaded for a weekend trips. I have noticed the last couple of times out that the temp gauge will start out at normal temp 200-210, but then drift down to 175 or 180 while going up hills and then coasting on the downhill. It does not correlate with the fan clutch engaging or if the A/C is on. I have never had a service engine soon light come on in the message center box.
No leaks anywhere on the engine, coolant is at the proper level. 35,000 miles on the truck.
Drove the same route recently just towing the Seadoo jetski and the temp gauge functioned nomally. Took it to the dealer and they could not find any problems. I am fast approaching the 36K mile end of warranty and I would like to get this diagnosed before it ends.

[ropinfool]

could it be the thermostat sticking open? allowing the water to over cool? Good luck. John

[Colorado Kid]

I've seen mine cool down on LLLLOOOOONNNNNGGGGGG downgrades, but I've never seen it get cooler on an upgrade, not unloaded and not pulling a 5th wheel.

[HowieE]

While thermostates do not normaly fail open I agree that is the first thing I would look at. Take a look on my web page for an example of failed thermostates. However that type of failure would give lower temperatures across the board.

[CareyWeber]

Originally posted by HowieE:
While thermostates do not normaly fail open I agree that is the first thing I would look at. Take a look on my web page for an example of failed thermostates. However that type of failure would give lower temperatures across the board. HowieE,

My 97 had a thermostat stick open on it and caused a SES to be set and no heat (The wife let me know that). smile.gif

The stealer said that the sensor was faulty, it happened again and then I got a new stat. :mad:

I think the thermostats in the 6.5's are made to stick open rather than shut.

Carey

[BuffaloGuy]

Yep. I get this too. Not always but sometimes. I'm thinking it is a stuck thermostat (stuck open). Maybe one or both. Mine are new though so it still makes me wonder.

OR

Perhaps when pulling hard and creating lots of heat the thermo's open up wide and then there is some lag time for closing. This would allow the motor to get too cool; At least until the thermo's catch up.

Ken