Newly rebuilt 2300SCR overheats when up on plane

[bkgoodman]

New long block - new thermostat, thermostat housing, impeller, elbows, raw-water pump. Manifolds inspected and pressure checked (all good), outdrive had complete seals and bearings replaced, etc.

Boat ran GREAT for the first 2 or 3 hours (though almost exclusively displacing). Temperature rock-solid in the center of the dial - (160? 170?)

When I get it up on plane (let's guess 3800 RPMs) - the temperature shoots up to 220-230. Back off the throttle and drop off plane - temperatures goes right back down. Repeat the test, and get the exact same results.

Any ideas?

[Phillbo]

Lack of water flow is my first thought. Were the hoses replaced as well? You could have one collapsing when you increase RPM's.

[pascavone]

I'd beat your water pump impeller is shot, for what ever reason.

crank the engine up at 3k at the dock and see if it happens, got nothing to do with being on plane, its the load.

you could be sucking air from a hole or you have the hoses backwards installed on the pump.

you could uses a compressor and blow the line back.

remember you have a power steering cooler, gasoline cooler, and a oil cooler as the raw water swings behind the engine.