I have a 351 in a '76 sea ray 240, just bought the boat as a small project. It runs good but starts to get hot if i idle to long or if I run at 2800 -3000 rpm. If i run the boat at 1800-2000 rpm it stays fairly cool. It has the yellow green red gauge so I'm not sure what temp but when I say hot I meen the very edge of red. I have done a full lower unit service, the old impeller looked great. I installed a new thermostat and found there wasn't one. i took the risers off they looked rusty so I soked them in an electrolisis bath for 24 hours each and pulled lots of rust out of them after it was done I flushed them with a hose and they seemed to flow well. I pulled the hose from the t-stat housing and it's getting more flow than a garden hose. My next guess is the circ pump. It's raw water cooled fresh water boat. most of my test are with my boat lift half way down.
