I don't disagree with the notion that the system could pressurize from a bad head/gasket, but the second part of your post (after all the work you did) you say the coolant level rises in the overflow from minimum to maximum after ten minutes of driving. Does it stop there or will another ten minutes of driving see you leaving a trail of green down the highway? The overflow is just a mini expansion tank that makes room for the heated water. I would expect the level to rise.

My own experience is if the engine temp reads low it doesn't necessarily mean the engine's running cool. It might mean the probe isn't covered with coolant. I managed to melt a valve seat into the head running an engine that was abnormally cool after a head gasket replacement. I thought it was great, running cool, until I lost compression in that cylinder.

Come to find that unless you make sure all the air is out of the galleries of the head when you fill the engine, you are pretty much putting a cork in your coolant circulation system. Some coolant will get through but not enough flow to cool the engine. The block can take the heat, but that soft aluminum head will take a beating with overheating. A lot of posts have said park on a slope with the radiator cap out and run the engine to burp the air out. I prefer to unscrew the air bypass valve from the top of the thermostat housing and fill the radiator until coolant flows out the top of the thermostat housing. Here's hoping it was just a bad radiator cap that caused your problems<img src="/forums/images/graemlins/cheers.gif" alt="" />.