This was all 4-5 years ago and  could be I was just overlooking something - but, couldn't figure out what it was, so pulled out the thermostat.

 

Ed

Sorry, I forgot about your plugs up deal. Years ago there was a sender of some kind in the top of the center iron. I placed my water temp sender there. When filling with coolant I could loosen that sender and almost all of the trapped air would escape. This why I have stayed with the make up tank idea since 1980. Some of the air will just not move out at less than full throttle. I like the air showing up in the tank, rather than sitting beside a hot spot killing the engine. In three heat cycles, there is no air left at all. I keep the tank 1/3 full for the whole season. it never uses any additional coolant. I pressurize the coolant until the cap releases after checking coolant levels.

 

I forgot to say that I use 10% antifreeze in the coolant. Racing in October can get rather cool.

 

Lynn E. Hanover