i have a 1989 Sea Ray Sundancer 300 Da with Twin Mercruiser 350 motors. Last season I bought this boat. Has about 1500 hrs, now has about 1600 hours on each motor. Ran fine when I first put it on the water. Then all of a sudden the starboard motor started overheating at idle In the spring time, I’m here in Portland OR , Columbia River area. I had this issue in the spring when there was dibre in the water. I took the boat and ran it all day. The problem then suddenly stopped. I ran it all summer and fall with no issues. Now the exact same issue is happening on the same exact motor. I have it on the water, what can I do to diagnose the problem? I just had this boat serviced, maybe I sucked up something into the system? Would it be the thermostat? I’m not even sure we’re to start? I see threads here staying it could be a hose or a spring. Any suggestions?