Fresh water cooled. I've changed Sherwood pump, manifolds, risers, elbows, all hoses, thermostat. Swapped heat exchanger with other engine. Burped the antifreeze. Hauled out checked strainer screens. Clean. Still overheats after 2-3 minutes at 3200. Help I am at my witts end! Could it be bad fuel?
l should add this is a carburated engine.
Addtl info: Inboard motors pull water from the hull. Switched out fuel filters (primary) and had a whole lot less white steam from exhaust. But only for about 15 minutes, then it came back. E10 Fuel around here. Overheat happens at 3200 after about 4 minutes on plane.Thanks for the help!
l like the clogged high speed jets in the carb theory.I am going to have it rebuilt this week.. thanks. The white smoke went away for about 30-45 minutes of slow-n-easy cruising after l changed the fuel filters. l guess I will be buying stock in Sierra. Thanks for the help.

Check your emission controls. A malfunctioning componet can cause it to overheat as well as vacuum leaks. Also has it been rebuilt lately? l had an engine overheating once and finally pulled the water pump and started flushing with a water hose and found a red mechanic is rag inside.

l never saw bad fuel do that.

Partially clogged hi-speed jets can lean an engine out to the point of running hot.

How is your oil pressure?

Compression?

Do the spark plugs tell you anything?

Have you put a heat gun or thermomelt on it to verify the temp reading?

Is ur water intake in ur drive or is it thru-hull?If it is in ur drive check ur water pick-up hose.It may be twisted or kinked. l have seen this many times before.Also u say u have changed the pump.Did u change the pump or just the
impeller?If only the impeller ur housing could be distorted & this will not allow it to pump enough water.To check & see if it is a water pick-up problem,by-pass ur drive & remove the hose inside the boat & put a garden hose in there & try running it this way & see if it still overheats.If so write again & let me know how much water is going out the exhaust.Good luck.

Check the circulator pump for leaks at the output shaft. If leaking, the pump is finished, replace. Check inlet and oulet hoses on the seapump are correct. Some of these pumps inlet form the bottom, some from the top, depends on motor direction. all advise from other is good, too.

Many area to look at> If steams out exhaust check the risers as the r Small holes in the ends to allow the sea water to exit> After time they corrode & restrict the water flow> Also the exhaust hose gets a small burn holes in it & under power it closes the exhaust 3'' or 4'' hoses & over heats the engine> If it been overheated then pull the exhaust hoses off the risers & look inside have found quite a few with this issue>Have also found if u have a muffler they have a flab inside that breaks loose & closes the exhaust> Hope this helps u but there r a lot of other things it could be also>If u have rear mount Heat exchangers than they had this issue to low u have to put an over flow tank higher than the exchanger> with a 7lb return cap> The water pump get an air lock & over heats> Try taking the hose loose at the thermostate & let the air out> Hope this helps>>