Hello all. Any suggestions would be much appreciated. A few days ago my temperature guage stopped working. I replaced the sensor with a new one from Advanced Auto Parts and after replacing I flushed the coolant and added with Prestone at about 60-40 coolant/water ratio. Now the guage works, but it quickly goes from completely cool to "hot" within a few minutes, even when driving on a 75 degree day. I replaced the thermostat last year or the previous year (can't remember) and before the guage stopped everything was fine. Bad sensor maybe? Or could have the flushing (used prestone coolant flush) maybe caused the thermostat to stick in closed position? During the flushing, as directed on the bottle, I set the heater to "high" for 10 minutes, then repeated with just water for 10 minutes and at these times the temp guage rose quickly to hot just as it did when running/driving. This is on a '69 Boss 302. Any thoughts?