Did a search and see this has been covered a few times. My turn. I have a 97 200 Merc that is overheating at about 3,500 to 4,000 RPM. Cavitation plate is about 1" below hull bottom. Water temp in the bay is about 65. Changed the impeller (kit) but not the entire pump. Put in new theromstates and gromets. Put in new poppet valve and gommet. Still overheats at about 4,000. I suppose I should go back and do the entire waterpump, but problem is at higher rpm and about 30 MPH, so water pressure should be from the pick up more than the pump. Which makes me think the poppet valve is not opening and allowing water to leave the heads faster. I'd like to trouble shoot the poppet valve (any suggestion?) I was thinking I could disconet the water hose feeding it (making it another pee stream) and if it doesn't over heat then I know it the poppet. Also was thinking of removing thermos and "back washing" by hose attachement next to pee stream (that sounds stupid now that I've typed it.) I won't be able to get it on the trailer for another week, so trying to do what I can in the water.
