Are we looking for an overheating issue or a fluctuating gauge? The gauge problem you described is commonly caused by a lack of a tiny bleed hole in the thermostat. Those are most often found on import engines. The heat in the coolant reaches the gauge's sending unit first, so the gauge goes up, then it migrates over to the thermostat which finally opens. At that point cold coolant rushes in from the radiator so the gauge goes back down and the process starts all over. After a few miles the gauge will settle down and stay steady.
I had this happen to my '88 Grand Caravan many years ago, and a few years AFTER the thermostat was replaced. Don't know why it didn't act up right away. Had one of my students drill a 1/16" hole in it and that solved the problem. I'm sitting in that vehicle as we speak. The hole lets a little coolant through so the heat gets to the thermostat sooner. It is way too small to affect the temperature it regulates at.
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Tuesday, May 20th, 2014 AT 9:19 PM
