Slant 6 Overheating

Well, well, well. Guess what? I found out the reason for overheating. And it had nothing to do with my radiator cap, thermostat, water pump, or radiator.

My motor was running waaayy lean! I had a small rubber cap blocking off a vacuum port at the base of my carb. It mustof been a real cheapie because it basically rotted and split. Didn't fall completely off, but was not sealing off the port any longer. So, I've been sucking lots of air at high rpms. :banghead:

I'm a bit surprised that I didn't notice it in the way the engine was running... I did notice something a little abnormal (running a little rough at idle, and cold start manners were off a bit), but it wasn't too bad.

ANyway, I got a kick out of this solution, and I thought it would be worth sharing. That explains why it starting running hot all of a sudden--the thing finally ruptured and the vacuum leak started abruptly.

Thanks everyone for the input and ideas!