Here's an odd one. My brother has a HEMI Magnum ( man, do I love that car! ) and he was in the parking lot of his work whipping what we call "shitties" ( circles ) and the car stalled on him and was hesitant to start. Ever since then, the car would warm up, and then the temperature would drop, the heat would stop working and a lightning bolt symbol on the dash would light up. The symbol has something to do with electronic throttle control.
I brought my OBD2 scanner over and we went out for a run. 25 degrees ambient and it was 4 miles of driving after a couple of minutes in the driveway and only got up to about 130 degrees Farenheight. He's supposedly a little low on coolant, but I can't imagine what would cause an engine to start running cooler after it warms up unless the thermostat is stuck open ( a likely scenario since the codes stored had to do with the coolant at lower than operating temperature, etc )
I've never heard of a car getting up to temp, and then cooling off. That and while cruising, his O2 sensor was ranging from .015 to .890 volts...erratically all over the place. That could be from the "displacement on demand" that the hemi has, or ???
Makes me glad that I drive two cars built in 1997. I like easy tech that I can still understand.