Temperature alarm

My father has a '04 or '05 20hp on his pontoon, the temp alarm will go off after about 5 minutes of idling in gear, but starts back up immediately, it can idle in neutral or run above idle in gear all day long with no issues, alarm only sounds while at idle in gear. The discharge water is luke warm while idling in gear, after alarmand immediate restart, discharge is actually cooler. He recently passed so I don't know what maintenance has been done. I did pull the discharge tube out about an inch because when I first put it in the water there was nothing coming out of the pee hole because it seemed to almost be kinked coming out of the cowling. Any advice is greatly appreciated.

Sorry no one has replied yet. I know absolutely nothing about the 20 HP, except that there are a bunch of different models. Recommend that if you don't have it, you first download the Owner's manual from the Honda Marine website: http://marine.honda.com/support.

That will tell you where to find the model number and serial number. Post those on this forum and see if anyone who knows more than I do about that engine responds.