Hello. Hope all of u guys are well.
I recently put in a new thermostat and had flushed the cooling system. I then proceeded to flush & backflush the heater core since I've never really had good heat. Its a 192 stat and my gauge never really rose above the quarter way mark on the dash (130,210,260) so it would ride about 180 I'd say. No heat but never had any other problems or any leaking fluids at almost 200K.

Then my gf drove it and of course all of a sudden the check gauges light came on, oil pressure dropped to zero, and then it overheated on her (I believe the thermostat was stuck closed). Long story short, I dropped the oil pan fearing the sludge problem but surprisingly clean, replaced oil pump, new gasket, then I ran motor flush that cleans the system. Fixed the oil pressure problem.

I noticed however concerning the heater (with a stuck shut thermostat mind u) that as soon as I would put coolant straight in the radiator after releasing pressure, the heater would blow hot air but as the temp gauge climbed up, the air would become cold again. So my father and I flushed and backflushed the coolant system, put in a fail safe stat, and filled with antifreeze. Drove it around a couple of miles and the heat was working great then as the temp gauge slowly climbed, the heater blew cold. Gauge ran to 210 (halfway) but no further. Flushed once again and then ran great with heat and the temp gauge at 1/4 of the way up.

On the drive home, the heat was blowing hot, then stat rose to halfway to a little past fluctuating between that area and the heat was doing the same, as in blow hot air to cool air to hot again. Then the overflow tank blew the cap off by the time I pulled in the drive. We did fill it way past the correct level so hoping thats all it was. Gonna drive it a little tomorrow now that the coolant level is correct on the overflow tank and see what she does. I would appreciate any input from anybody else who may been through the same or similar. Thanks in advance and sorry I wrote this novel lol

 

Just finished driving around for about 30 mins or so. The temp gauge never rose above 1/4 of the way and the heater was blowing warm to lukewarm which is way better than cold. Seems like everything is fixed and back to normal. Hope all ur rides out there are running great.

 

I'd suspect the heat issue would be because when the thermostat opens less water is going through the heater core.




By the way, there aren't sludge issues with these motors, only with people who don't maintain them. It's not at all uncommon to get well over 300k miles out of these motors.

 

Appreciate the input and diagram. That def makes sense. As far as sludge buildup, I purchased this Durango with already high mileage and had a quart or 2 of cheap oil containers in the back. Some of these forums mentioned something about sludge but I run synthetic oil in my vehicles and keep up with maintenance. Needless to say, sludge def wasn't the problem. If only i could be so lucky to have a vehicle make it 300K. This D with 200K is the most miles I've ever had and I only put 10K of those on it. Changed the oil 3 dif times, all synthetic oil. Thanks again for the input