My '98 Volvo Penta 5.7 is overheating. I just bought the boat and changed the thermostat, and there wasn't any water in the thermostat housing. However, there was water in the block and exhaust when I removed the drain plugs. The boat is out of the water, so I can't perform pump tests. Everything is so hard to get to does anyone have any good ideas about what to check next?