Car is in the red on the temp gage then goes back to cool then back up to red what cause this?

Answer 1

Hopefully your car isn't really getting that hot. I've heard that if the temperature sensor is grounding out accidentally it can read the maximum temp. Check for a loose wire or frayed one. Perhaps you can get someone to jiggle the wires to it while you watch to see if the gauge jumps. If you can find the specs of what the temp sensor should be reading then you can check it's resistance with a digital multimeter. Normally the temperature sensor is just a resistor that changes it's resistance based on it's temperature. Usually a high resistance when cold and a low resistance when hot. And if it's periodically grounding out - the resistance would be low, causing the high temp reading.