On my 1971 bus I have been having trouble with it blowing out the antifreeze when at full power. Level cruising , or mild grades are no problem but steep mountain grades and the antifreeze goes right out the overflow vent. This the 392 non improved cooling. What have others done to improve the cooling on these engines? as long as there is enough antifeeze it does not overheat and is not overheating when it vents. I believe it is getting hot spots and boiling the coolant locally causing the radiator pressure to rise above the cap pressure and then venting. There is no signs of head gasket leaks, and this only occurs under heavy load.