Temperature problem, 2000, 4.7L

[alexandbuck]

I have an interesting problem. A friend asked me recently why the Durango was not heating up on an eight mile commute like it used to. The Durango has 60K miles on it. I immediately figured it was the thermostat so I replaced the original with a new 195 degree Stant. I thought it was odd that when removing the lower radiator hose that only about a gallon of fluid came out but thought maybe wierd geometry in the construction may be the answer. The old fluid was not the nice bright green of new fluid. The fluid level was checked before doing anything as that would also cause a lack of heater heat. The opening at the engine at the thermostat was fairly clean and not sludgy. I just took a 100 mile trip in the Durango today and the heater worked well. The temperature however would control at a constant point at 50mph and lower. Temp outside was 40 degrees. When I ran 65 mph the needle would rise to over 230 degrees. My first thought was that the new thermostat was not Mopar and may not be passing enough water. My second thoughts are that maybe there is a blockage in the radiator and not allowing enough flow. Maybe there was nothing wrong with the original thermostat and the heater core is working better because it was flushed with the replacement fluid and not completely blocked. The original thermostat was checked and it opened in boiling water on the stove. I think I need to flush before replacing the thermostat again. What is the procedure for a flush? I could not find a drain for letting the fluid out and replenishing while running. Does this sound like the right thing to do or does the thermostat need to be Mopar. There is a major difference in thermostats between Autozone and Advance. The autozone unit is $35 vs $22 at Advance. I need to make better before it gets 90 degrees outside.
Thanks, Alexandbuck

[alexandbuck]

I replaced the thermostat with a Mopar and everything is good now.
Alexandbuck

[DurangoDave]

Alexandbuck-
I never would have thought there was a need to specifically use a Mopar thermostat. I would have put in NAPA, Autozone or whatever... just as you first did.

You have me interested now....before you put in the Mopar did you compare it to the aftermarket thermostat that didn't work? What is different? Size of the opening when the thermostat is in the open position?
thanks
Dave
Westminster, MD USA