1993 Plymouth Sundance 2.2L with TBI 36K miles My temp gauge seems to constantly fluctuate from below the 1/3 mark to slightly over the 3/4 while driving. It will sometime sweep the distance back and forth, sometimes it will stay at the 1/3 mark, and then heat up to 3/4 mark at stop signs. I have tried almost everything to solve this problem, with no success. 1. antifreeze flushed and replaced. 2. tried 4 different thermostats, including 180 degree 3. tried drilling 1/8 pin hole in thermostat housing 4. tried 'burping' coolant several times 5. new radiator and hoses 6. replaced head gasket (head was apparently warped) milled and checked for cracks The problem persists. The mechanic doesn't know what to try next. He says it's not the gauge, since he ran it on the scanner. He said the 1/3 mark is approximately 190 degrees and 3/4 mark is approx. 217 degrees. The fan turns on at 217 degrees, according to him. I know this type of fluctuation can happen in colder temperatures, but the fluctuation on this Sundance happens in any and all temperatures. Heater works fine. I first noticed the wild fluctuations going through the Rocky Mountains, going down long declines (not the inclines!) with engine rpm winding up from gravity, the gauge would sweep radically back and forth. The problem persists, and I am concerned about warping the head again. Running out of ideas and money. Can anyone help, please?