Hot?...
From what I understand, your not running hot while your on the water hose, correct?...
Hook the water hose back up to the ski, start the motor. Turn on the water, then look at the back of the pump nozzle. Do you see water coming out? If not, then your pick up tube from the pumps nozzle is blocked.
In the high pressure side of the nozzle, is a venturi pick up tube. This is where the pressure from the nozzle, supplies cooling water to your engine. If you see water coming from the pump, that doesn't mean you don't have restriction.
The water hose has the pressure to "force" water into the engine for cooling. Your engine seems to run well except for the cooling. You'll need to start at the inlet of the pumps nozzle, follow the water flow path through the engine and back out. Something is blocked somewhere.
In the worse case scenerio, the water comes into the engine via the exhaust manifold. Then, enters the water jacket at the lower end of the cylinders water jacket. If this ski has been rode near the sandy beach or muddy bottom of a creek, then you may have partial blockage in those water jackets and they'll have to be removed and cleaned. THIS SHOULD BE A LAST RESORT........
Look for blockage in all hoses and elbows, with the engine running, use the water hose to continue to flush your system, maybe pushing the dirt and trash out with it. Then, the pressure from the jet pump may be sufficient to keep the engine cooled.
If the temp sensor alarms on the water hose, you'll want to check the sensor for proper operation..........:cheers:
