Strange thing on our '00 Durango. Temp gauge reads low and the heater works good, then all of a suddden the temp gauge goes up and the heater stops blowing hot.
A shop replaced the t-stat last year and I'm thinking they put a failsafe t-stat in it and it's
stuck open? Coolant level normal. I'm going to change the t-stat myself with a regular type.
How would I know if the t-stat is stuck open without taking it out? Advice? Thanks!

 

You could try and feel the hose when you know the engine is cold and try to tell if there's a lot of coolant going through it when there shouldn't be.

What engine do you have too?

 

It has the 5.2L engine. I hope it's just the thermostat.
I just saw a video of changing the t-stat and the guy used RTV
on both sides of the gasket. Is that overkill? He also removed the
ac compressor, is that really necessary? Seems it can be accessed
by removing just the alternator? Thanks!

 

It could also be the condenser on the dash they have a problem of clogging up

 

Check your fluid level as well. This will happen if it's low and the water pump cavitates for a while while the air passes through it. The 4.7's need to be "burped" when they're filled. Not sure about the other models.

Bob

 

I know for sure the 98s and 99s (only had the 5.2 and 5.9) don't need to be burped, but I think they changed around the radiator and hose setup for 2000, so I don't know if they need burped or not.

If it helps any, this is where the temp gauge sat on my 5.2 with the stock temp thermostat.

 

Check your fluid level & make sure you get under your Durango while it's the engine is running to check for leaks. My 1999 Durango was leaking from the water pump. The pain with that was to get the Fan Clutch off which I did using a 36mm or 1 7/16 open wrench & a long pry bar in between the water pump pulley & water pump.