Greetings:

I have a 2008 Supra Launch 21 SSV with a CAT 340 Assault engine. I put in water this week and not long after launching the temp ran over 200 degrees which triggered a warning on the dash. I shut the bout off and checked the engine.

This happened once before when I sucked some muck up when I parked the boat on a beach and it worked itself through after alternatively running and cooling the engine.

I took the approach to running and cooling the engine this time and it has helped to a point where I can see the engine temp rise up to about 180 degrees then drops to 155 degrees then back up to 180ish and back down. After doing this for a while, I now have the engine stabilized at 160 degrees (which has typically been the engine temp on the hottest of days). However, the water is 58 degrees and the engine should be running in the 145 to 150 degree range.

I changed the impeller approximately 5 years ago but this doesn't seem to be the issue as the engine was alternatively heating and cooling. I'm thinking it might be the thermostat. I'm not sure where the thermostat is and hope it is accessible. Anyone have any other thoughts on what the issue could be?...thanks in advance...John