head gasket

tonight the car was running fine, its frigid cold and i have a new 160* thermo in it, for about 3 weeks now. i was on the highway and just noticed the car hit 260* or so the gauge said. i checked the coolany (fine) i checked the oil, seemed low so i added some even though the car ran just perfect. It's odd what happens.

starting up is normal and it seems to warm up fine, but then it will sky rocket and stay there occasionaly coming back down to normal temprature just as quickly, no matter where it occurs it acts the same. i bought a fail safe thermostat so if it failed it should have failed open. regardless hopefully it is a thermostat problem? it doesnt seem to burn anything other than oil as it is an older engine, but even when this happens it runs just fine, never sluggish or erratic idle.

It sounds like a thermostat. Very abrupt temp change from low to high.

like air pockets? i hoped so, ill change it tomorow and see if it resolves itself, the coolant needs to be changed and i think that the goop in it may have caused the failsafe thermo to get stuck...which i suppose in 25* weather during the winter is entirely feasible.

Is your coolant overflow tank bubbling?

Is your radiator cap cold even though the engine is warm?

thermo stuck, rad cap was cold, must have boiled out, its running perfectly fine now like nothing happend....