Alarm sound when going 2/3 throttle more than 5 min

[dingopointer]

Hello

I have 96 C150TLRU outboard. It runs great all day long until i try to go past 2/3 of the throttle. after few minutes it sounds the continuous alarm and boat looses power. If I do not turn it off it will shut itself down. If I turn it off and turn it back on the problem disappears and I can use the boat as much as I want until I get it past 2/3 of the throttle again.

This is a basic engine where you premix the oil and fuel.

The motor does not seem to be too hot inside and the water shooting out is not hot. It starts right up any time.

Any ideas? Please help - any suggestions are welcome.

[mitch]

tell tale water will be cold as that comes out before going through motor have you checked the water pump thermostats and water bypass valve

[99yam40]

Pull and test thermostats, PRV, and sending units for proper operation. Check passages for blockage and change water pump and look at the housing for warpage.

[amlorenz]

I had the same problem in my motor and ended up being a bad impeller in the water pump. At lower RPMs it seemed to be able to pump enough water to keep the motor cool but as soon as I would get past 2500 rpms the alarm would sound after about a min. I also had water coming out of the tell tale the whole time and the motor never felt warmer than usual.