60 hp Mercury overheating

Ok guys I have a 1987 Mercury 60 hp that over heats at high speed. Like over 4000 rpm's. It will not overheat at lower speeds. This problem has been gong for a couple years. This is what I have done so far. I have had 3 new impellers installed and that has not fixed the problem. I took the back cover off the rear of the block. That exposed the water jacket. I did find a chunk of impeller in there, and thought that might have fixed the problem. No luck. I have been told that I should pull the head to see if there are any other pieces lodged in there. Your thought's are greatly appreciated.

Any suggestions??

Steve

That motor has an undersized impeller to begin with, so anything restricting water flow is a serious problem. There may be more pieces of impeller trapped in there. You'll have to remove the left side exhaust plate to find out. In doing so, remove the thermostat and throw it away--every one of the dozen plus triples I've worked on had them removed (by Mercury).


Jeff

I took the side exhaust plate off and did not see anything in there. Also there is no thermostat on this engine. I called Mercury and gave them the serial number and it was verified that there was never a thermostat on it. A friend said the head was easy to remove, but I am not so sure about that.

Steve