I'm trying to figure out why my 1997 Chrysler Concorde keeps intermittently overheating. The car has a 3.5 V6 and 125K miles. About
10 months ago I was driving on the freeway and I noticed the heater was not working properly. The air would blow somewhat warm and then start blowing cold air, and then back to warm air. Suddenly, the heat gauge went to the "H" red line. I quickly drove off the freeway and stop in a parking lot to turn off the engine. I tried to add some water to the system, but the engine would still run hot. I had the car towed back to my home. The next day I added water/coolant to the cooling system - poured coolant directly into the engine block via the thermostat housing and added coolant to the system. I also replaced the thermostat. This seemed to work, because the car ran normally with no overheating problems for 9 months...About a month ago, the same thing happened. Same scenario - heater wasn't working properly, engine overheated and I drove the car back home a few miles. I waited about 15 minutes before starting the engine and driving the car back to my home. I said, "It must be a bad thermostat." Again, I filled up the engine block and cooling system with water/coolant, and replaced the thermostat with a "premium" thermostat. The car ran perfectly for a month.
Today, the same thing happed yet again - heater wasn't working properly (changing from warm to cold and the heater would turn on and off by itself), engine overheated, and, in addition, a very noisy valve lifter chattered away while I was trying to exit the freeway to park the car in order to turn off the engine. Also, at this point, the car had lost about half of its engine power and stalled out when I parked the car. Yet again, I had the car towed back home...
So, it seemed like the car was losing coolant at some point, but there were never any noticeable leaks anywhere. Also, during the overheating problems, I could hear a lot of water flushing and gurgling in the heater core area. As if there was not enough coolant in the system. Also, I could always smell a slight odor of coolant when I sat in the car over the last year. I never could smell coolant when I opened the hood.
I looked under the car to see if anything was happening. I noticed that the tailpipe resonator was dripping water. There was a 3 inch wet spot where the resonator joined the tailpipe. So, maybe this is where the coolant was slowly disappearing to.
Well, I was hoping it would not be a head gasket problem, but that looks like the issue. Or could it be some other component that I overlooked - radiator, water pump, hoses??? Many Thanks!