Hot horn comes on after a long idle

[bigbass21]

I have been chasing this down for a long time. When I idle out of the trees at 1000 to 1200 rpm after about 200 yds the hot horn comes on or when I hit the throttle to take off it will come on. I turn it off and start it back up and it will sometimes come on until the boat planes out then no problems. I have changed out the thermostats, temp sensors, rebuilt poppet valve, rebulit water pump, changed the filter in the water line that cools the compressor, new impeller. I run about 20-25 lbs of water pressure at wot. Anyone else ever had these issues?

[boats.net]

Verify you do not have water passage blockage. Would not hurt to run a head temp to see if it is actually over heating.