Sport Jet 90 Overheating horn Sounds

[Gravel Grinder]

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I have a 94 Tracker with a Sport Jet 90 and the overheat horn sounds off with in 1/4 mile of take off. The water pressure gage will show 0-3 pounds of pressure at WOT. I checked the 130 degree thermostat in a pan of boiling water and it is fully open at 140 degrees. I put the thermostat back in and had the same problem. I then took the thermostat completely out and still have the same problem. I took the thermoswitch out and heated it with a hair dryer, I was able to get 190 degrees with a electronic thermometer lying next to it. I checked the cicuit with an ohm meter and it never closed the switch. I took the exhaust manifold off and it only had an 1/8 inch of gravel in the bottom of the manifold. I took off the water line and set a funnel in the hole and poured water down the hole, the water would flow freely. Any suggestions?

Thanks,

[merccoop]

I rebuilt a sportjet 90 for my father who bought a jetboat with one in it for 200 dollars not running. After I rebuilt it, he said he was overheating also. He checked everything you did, but realized that the oil injection line was pinched. I am sure my dad's probably now has some damage to it, but anyways, its a suggestion. inspect the oil injection unit, I guess if it has it. I don't remember what years had injection and what years you had to premix. Besides that, it sounds like you've done a good job at diagnostics. Isn't that so frustrating?!