Coolant Overflowing when Gas Pedal Released
So about a month ago after driving home got out and all of a sudden heard a waterfall coming from under my truck. Looked and coolant had leaked out. It was a nasty rusty brown colour.
Flushed the rad, etc and made sure the water was clear. Also used a rad flush product. Then filled it back up with 50/50.
Everything seemed good till a couple days ago when driving on the highway got a "check gage" as the coolant temp gauge hit red and then went back down just as fast. The heat then cut out and only came back on about 5 minutes later.
Changed the rad cap and "burped" the rad as the top hose was collapsed/flat.
When burping the coolant was a tad bit frothy and was once again rusty brown. Also whenever I would let the gas off from having rev'ed the engine the coolant would overflow from the top of the rad (literally boiling out). I could get it to go back down by rev'ing again.
Have no idea what might be wrong. I'd replace the thermostat but stripped a bolt and it's stuck solid even after trying stripped bolt remover, etc.
Did a search, but didn't find anything to help.
Any thoughts so I can drive without worry and with heat?!