Overheat Alarm

[ranger]

Hey, Maybe someone can give me an idea. Yesterday I took off from the dock and went about 3 miles down the Cumberland river. Boat was running well. My overheat alarm in the control box went off. I immediately shut down the motor and waited for it to cool. When I started it back up the alarm was still going. I was getting a good constant stream from the telltale hole and the heads were hot but I could touch them. I hated to do this but I had to run it back to the dock. The motor would not go over 2000 rpms, but it ran well (I didn't hear things coming apart) and we made it to the dock. It even started back up and went onto the trailer ( the horn was still going). Today I went out and turned the key and the horn was quiet.
I put the muffs on and let it run for about 30 min. No horn.
Water felt cool coming out. I started it up again and the horn started sounding. I fell the water again and it was hot. I pulled the thermostats and they looked like they had seen better days, so I will replace them.