is this a blown head gasket ?

fishy68 said

It's perfectly normal for pressure to build up after the engine warms up because coolant expands as heat is applied. It is also normal that if you remove a radiator cap from a hot engine to have it spew the antifreeze out so it's not a good idea at all to do so. I've seen guys get major burns doing that. If your car runs good and doesn't loose coolant you have nothing wrong. If it builds too much pressure it'll puke it out of the overflow hose/tank. That's when it's time to check things.

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Will puke out of overflow sometimes too is normal. I agree with all. If temp gets too hot, take out thermostat and check with boiling water on stove then drop in after boiling starts. If it opens its good. All cheap thermostats suck. We have gotten 3 bad ones in a row and took them back. Pay the extra $ if you have to get one. We went back to the original brass on from 69 after CLR cleaning! Good Luck. Also you could put on aftermarket overflow bottle and you would not have to take cap off.