I have a 2000 ch613 with a 1996 remaned engine that was swapped in. It had to be retrofitted with a tubular style oil cooler because the pancake style one was slightly different in shape at the mounting area to block. Some of the plumbing had to be changed as well. The tractor appeared to be overpreasurizing and was blowing out of the over fill. I took everything apart nothing clogged ,changed water pump no cavitation on housing,changed thermostat, air compressor,did combustion test as well negative . Still does it but not all the time loaded or empty. Temp gauge will go up high cold air will start blowing out defroster shut truck off about 60 seconds, start it back up temp goes immediately down and blows hot air again. I drained the fluid out last night and got 4.5 gallons of antifreeze out I took a coolant hose off air compressor blew a little air through it gurgled and then then another 3 gallons came out. I filled it back up it would only take 4.5 gallons I disconnected the small hose that goes to the fill tank blew some air into it it gurgled again and took 3 gallons of antifreeze.whats going on I feel like its getting airbound especially since it does not do it constantly. I had it over at the dealership they did exactly what I did only thing different they did was change from a 2 piece tank to a steel single tank . Still does same thing they tried bypassing the air compressor also and did a combination gas test so it's not a head gasket.