When I bought my boat in 2000, the PO said he had gone to great lengths to track down a strange problem, without success. The engine ran fine, but after a long day motoring you had to manually transfe coolant from the header tank back into the engine. It wasn't until more than a year later that we started to have overheating while motoring down the ICW. We limped into the Palmer Johnson yard in Savannah thinking this is going to cost a small fortune, but they turned out to be quite reasonable with great mechanics. There was a small leak in the header gasket, so that when the engine cooled there was no suction to pull the coolant back into the engine. We did a minor rebuild and the engine has run great since.