This just started at the end of last season and this year when I dropped in after performing yearly maintenance on the boat. I replaced the impeller and thermostat. I have an oem fresh water cooling FULL kit on and have the right thermostat all parts come directly from indmar. When sitting idle for long periods it will over heat as soon as I punch it to full throttle or even gas it up a bit it cools straight back down. I live in the middle of no where and there's not any mechanics that will touch this boat so I need some ideas as to what it could be so I can fix this issue. Obviously between switching riders and being in the no wake zones this could get kind of tricky if I don't get it fixed. I appreciate the input thank you!