Engine cooling problem

This is a problem that I have been trying to work out now for the morning and cant seem to figure out.

When I start the car everything is fine and the fast idle works. Once the engine starts to get up to temp where the thermostate opens up is where the weirdness happens. The temp gauge bobs up and down and then once it gets around the normal operating temp is just climbs all the way up to H and a bit past then I shut it down. After like 30 seconds off I put the key in and check the engine temp and its already half way down the temp gauge. I opened the block bleeder bolt and the rad cap and let the engine run to see if somthing could happen once the enging temp starts to spike steam starts to come out of the bleeder hole and I start to get coolant on the ground not alot but I cant seem to figure out where its comming from. I have been told that this sounds like I am getting steam around the thermostate or like there is vapor traped. If anyone might know what I should do here I would appreciate the help since this seems to be the only bug in my new engine.

The first thing i would do is find where the coolent leak is, pressurize the system if you have to. That could be what’s causing the vapor lock and all the problems.