I don't understand the symptom. The temperature gauge is too low? The air from the heater isn't hot enough?
If you start out with a cold engine, then the temperature gauge rises too high after a couple of miles, suddenly drops too low, then does that again perhaps as much as four or five times, then stabilizes, that is caused by the new thermostat doesn't have a tiny bleed hole in it. The temperature sensor for the dash gauge is reading the coolant temperature where it is becoming hot, but that heat hasn't migrated over to the thermostat yet. By the time the thermostat gets hot enough to open, the dash gauge is reading too hot.
Once the thermostat finally opens, and coolant begins to circulate, the cold coolant in the radiator rushes into the engine, then the gauge drops down again for about a minute. That causes the thermostat to close, and the process starts all over.
The solution for that is to drill a tiny 1/16" hole in the plate in the thermostat. That allows the coolant to flow just fast enough for the heat to get to the thermostat and let it open a little earlier.
Why was the thermostat replaced originally?
Wednesday, April 5th, 2017 AT 3:10 PM