A little while back I posted about this problem. Since, I have reringed it, valve job, new gaskets etc. While down the block was checked and cleaned by spraying and using air for any crud or sediment, the water pump looked fine and moved water while spinning it in mop sink,the rad was flushed with CLR and even a weak mix of muriatic,when put back together it was flushed and back flushed again, timed correctly per manual. Tractor runs great, but using inf thermometer head and block will rise to beyond 200 degrees and will eventually push the coolant out. Takes about 20 minutes of running but it gets there. There is no thermostat in it currently, doesnt matter if its 50/50 mix or straight water.. Same result. Out of ideas and patience, never dealt with anything like this in 30 yrs of various brand of antique tractors..