High Engine Temp

96 Dodge Neon. My Son had told me that the Temp gauge was maxing out. I checked it out ,thinking that it was the thermostat I replaced it. I thought I was sucesful. Siting in the car the temp gauge looked good. Then I turned on the heat, the gauge then maxed out. The coolant looked good to the eye and water levels are OK. The engined showed no signs of over heating besides he gauge. The radiator fans work. Any sugestions

I don’t think you have an overheating problem. But an electrical problem. Because what you describe is the exact opposite of what should be happening.

If the engine is indeed overheating, when the heater is turned on the temperature should drop on the guage. That’s because the heater core is just another radiator. Only smaller. But because the guage shows an increase in temp when the heater is turned on sounds like more of an electrical problem. And a bad ground can cause this. But where? That’s where an accurate wiring diagram becomes very handy.


Thank You for your reply. Being a electrician (not auto) the thought did cross my mind. But where to start? Guess I will have to get a schematic and jump into it.
God Bless

If there’s a public library nearby, most have free access to the ALLDATA website. Here you can copy accurate wiring diagrams for your vehicle.