I don't know what engine you have, but since most babbit engines are in "engine heaven", I will take a stab at this. If I had the water pump off of an unknown 55+ 235, I would try to scrape the accumulated sediment out of the rear of the block water jacket. With the water pump removed, the later engines have enough space enabling you to stick a pressure washer wand in the water jacket. There seems to be a recurring trend of folks having overheating issues that trace back to clogged water jackets in and around the number 6 cylinder.
