Is this overheat buzzer behavior normal?

[pcrussell50]

​So I have a 1986 Yamaha 40 with a fresh powerhead. Only a couple of hours on it. Starts and runs like a champ. Idles nice, accelerates under load without any hesitation, etc...

Had it out two days, one hour running each day and the went like this both days:

Started like a champ
Idled out through the no-wake zone (ok, well bumped it up to 1000 rpm just to get out there faster), about five minutes
Drive around at 3000 rpm
Drive around at 4000 rpm
Find a place to beach and swim and eat lunch for an hour or two
Fire back up and motor around between 3000 rpm and 4000 rpm
all perfectly normal operations
Idle back through the no-wake zone to Drop wife off at the dock to go get the trailer (well trained wife)
back away from the dock and find a shady place to shut down while I wait for her (Mojave Desert Lake Mead 100^F outside)

Wife shows up with the trailer, fire it back up after sitting 20 minutes shut down and... overheat horn starts up at idle. Since I am in the marina, I cannot bust up onto plane to see if it goes away. Horn keeps going as I idle back onto the trailer. Embarrassed.

This same chain of events happened pretty much as describe, two days in a row.

Outside air temperature low 100's, water temperature low 80's, telltale stream looks healthy at idle and under way. My 2.0l 150 and 2000 Mercaha 90 FourStroke handle these conditions just fine. Never an issue.

Any ideas?

-Peter