Random overheating

[e30Villain]

My car has been driving fine for a while now and yesterday it randomly overheated in 70 degrees weather, so I waited for it to cool and put some water in it. I drove to my friends house and let it idle for 20 minutes and drove for another 30 and it didn't over heat. The car had coolant in there for sure because I filled it the day before. I think the thermostat got stuck closed because coolant was spilling and obviously some kind of pressure had to build. I replaced the thermostat 3 months ago, why would It get stuck...?

[vpilarrt]

Have you bled the system since you changed the themostat? Checked the fan clutch lately?

[e30Villain]

My fan clutch is fine and I bled the system right after the thermostat replacement. And correct me if im wrong but a non-op fan couldn't cause pressure in the system enough where the coolant comes gushing out, right?

[jlevie]

Three things will cause the cap to lift and dump coolant. One is a bad cap or expansion tank, one is an overheat bad enough to boil the coolant, and the last is a head gasket leak that is pumping air into the cooling system. A serious overheat or bad head gasket can result in a surge of coolant out of the expansion tank when the cap is removed.

[e30Villain]

Just took out thermostat and tested it. It wasn't opening so I replaced it. Thanks for the help guys!