Well, wife and I went for a ride the other day. She got a little chilly. I stopped and threw the valves so the heater core was open and the bypass was off. About 5 minutes later. The temp idiot light came on but the gauge showed it wasn't over heating. So I quickly pulled over. Turned off heater core and turned the bypass back on. Less than a minute the temp light went off. Tried again and same thing.
So I left the heater core off and bypass on and came on to the house. Then today was checking a few things out. And remembered what Joe Breaux said about the bleed screw at the top of cylinder head. Sure enough there was air there. After burping the thing a few times while running with bypass off and heater core on. It idled fine not over heating. Putting out good heat for about an hour or so.
Turned off for 30ish minutes. Started back up. Within 5 minutes the temp idiot back on. A few revs and it went off. So I'm guessing there's more air around the gooseneck for the head. Guess I'm going the have to let it run, then burp, then off, let cool, burp, run to operating temp, burp, cool, repeat. Until I get no air.