I had a Fiero 1985 sitting a while. Put new coolant in. However, the gauge after a 10mins goes to Red. I got worried so I shut down the car. What could it be? Does it need to be Flushed? Is it a Fan? Is there a Fuse for the Cooling Fans? In addition, could it be a Thermostat?
Did you burp the system correctly. That is usually for first cause. Remove the stat and burp will and leave it out and see if it still gets hot. If so let it cool and check for more air.
