'07 HPDI V-Max 200 Overheats

[rfaas]

The motor is on a 23' tunnel hull and has sixty (60) hours on it, is used in salt water and is thoroughly flushed after every trip. It runs fine when I leave the harbor and the tattle tail has pressure (9 psi) a few seconds after starting it. Later in the day after making a few stops and then starting, it takes a couple of minutes for the tattle tale to flow and the alarm goes off. After letting it cool I'll start it and increase the idle speed and it starts pumping right away (the idle speed doesn't need to be adjusted). It doesn't happen all the time just occasionally. I've replaced the water pump impeller and it's still happens. Any ideas? thanks

[boats.net]

Check the thermostats and high pressure control valve to see if stuck open.

[rfaas]

That's what I was thinking, just wanted to hear it from an expert. Is it very difficult for a "side the road mechanic" to repair. How long would it take a qualified mechanic to repair. thanks