overheating

We owne a '91 Ski Nautique, 24 hp PCM Ford 351 with 1:23 PCM transmission. It starts, warms up and operates correctly--except that after pulling a skier, or otherwise coming off plane, the temperature spikes from approx. 160 to 200. This is "cured" by reving the motor until the temp. drops.

We have owned the boat since new. It now has many new parts (ie, pumps, hoses, sea strainer, trans. cooler, exhaust manifolds and risers.) We think we have elimated any air leaks. The sea water pump works correctly (15"/5 gallon test okay). The 143 thermostat has been changed and works correctly.

Is our muffler the problem? How can that be tested?

Are we okay trying to flush the motor with Limeaway or a similar produce to reduce rust and debris? (We do not have a history of lost impeller parts.)

Any suggestions are appreciated.   Thanks very much.

Thanks. The boat is in the shop now, and I believe my mechanic has done various IR tests. He states that although the exhaust manifolds are normal temp (120?) the engine itself ( valve covers, block and oil filter) are hot---the engine just isn't dissipating the heat. I'll have him try the Ohm test you noted. Thanks

Thanks for your comments. The boat is in the shop. I think various IR tests have been done. I'll have my mechanic try the Ohm test on the sender. He says the motor isn't dissipating heat well, and the motor (block, valve covers and oil filter) are hot, although the exhaust manifolds are "normal" at about 120. The temp. spike is quite dramatic and it goes up 30 degrees or more, so this is in excess of the normal swing expected when the boat comes to rest. Thank you for your comment.

I'm also starting to agree with Pete that you may not have a problem.

Thanks. Actually, we did have an air leak (leaks) but now think that issue has been eliminated with new hoses and other changes. No air bubbles appear in a clear hose (running from impellor pump to thermostat). We are running out of the "easy fix" options. Thanks again for your input.