175 hp Yamaha with hot alarm

[Hunterhja]

I have a1997 Yamaha 175 hp. Lately I've Ben getting a hot alarm when I run 35-40 mph. It will run all day at 30 mph with no problem. Top end is 65 mph. My pressure gauge does funny while running. At idle sometime it shows 2-4 psi, other times shows nothing. While running at higher speeds it may start off at 20 psi, then at the snap of your fingers pressure falls to 12 psi. Pressure may go up are fall even further to 8 psi at a finger snap. Pressure varies constantly. I did install a new water pump kit and new housing. Did not help my problem. I got this motor new and has never been in salt water. Any advice on what I should look at next would be deeply appreciated. Thanks.

[dubber]

Can you run at WOT without overheating? Suggestion would be to check / replace the poppit valve.

[ausnoelm]

Thermostat, poppit valve, then build up in the cooling passages, which unfortunately is the most probable.

[zenoahphobic]

This is running as two threads. Crossreference.

[Hunterhja]

Thanks. I have checked the thermostats. They appear to be fine. Put them in hot water and they open, took them out and they closed. Have not checked the poppit valve yet. When I removed thermostats I saw very little as far as build up. I will look at poppit valve then flush the system. Will post the outcome. Thanks.