My first post here - wonderful site! Have the same engine in my parent's 1992 Freedom 38 (since dad payed for engineering school, I've been designated "chief mechanic")
Lots of good suggestions so far, especially about underloading the engine. These little beasties are made to run & run hard. I've got a small diesel tractor that I often run at max rpm - in several hundred hours of use, it has never missed a beat.
A few added comments/suggestions:
1 - Proper antifreeze level? any evidence of leaks?
2 -Can you replicate the problem? We had an experience where we overheated for no apparent reason, we suspect that we had sucked some seaweed towards the strainer & when we shut her down, it dropped away. Problem self resolved. Make sure you have an actual overheat issue & you're not chasing your tail.
3 - I heartily recommend adding an actual temperature gauge if you don't already have one. We cruise at 2,9000 to 3,1000 RPM ~6 knots. Temp is the same as if we were running at 2,000 RPM. If we push her to max throttle 3,500 rpm (woods hole against the current for example) the temp will run up 10-20 degrees.
4 - regarding the "over prop" issue - what is the max RPM you can get the engine to turn under power? As others have mentioned, should be w/i 10% of 3,600 rpm. If you can't get to rated rpm, don't immediately blame the prop, we've had an issue with a bent shaft/strut (hung up on empty mooring next to ours during storm) "robbing" power.
Hope this helps.
Last edited by hazmat17; 09-28-2007 at 09:54 AM.