I have an 87 that the temp gauge started running right up to 300 degrees. The car is not hot, it does this in the driveway after running for 3 minutes. Everything under the hood is cool to the touch except the exhaust. I replaced the thermostat, the coolant temp sensor on the drivers side head and the computer coolant sensor on the front of the lower portion of the front of the intake. No improvements and yes the car does have coolant in it. What to do?

WHAT IS YOUR OIL TEMP ? IF YOUR COOLANT TEMP IS 300 IT WILL BE BOILING OVER... IF YOUR OIL TEMP IS 200 YOUR WATER TEMP IS PROBIBLY 150... SOUNDS LIKE A FALTY GUAGE... IT WOULD TAKE A LONG TIME TO HEAT UP THAT HIGH AT 300 DEGREES OIL TEMP MY 92 HAS A HI OIL TEMP LIGHT THAT WILL COME ON... AND YOU CAN TELL ITS HOT REALLY HOT.... IF YOUR WATER TEMP IS 300 YOUR OIL TEMP IS AROUND 350-360 YOU WOULD BE SMOKIN..........AND AS A LAST RESORT YOU CAN IGNORE IT ?!