04 F225 water pressure

I just purchased a used boat with a F225. The warer pressure guage only registered 0 at idle to about 2500rpm and 10 at upto 4500rpm. The pisser on the side of the housing shows water flow at all rpms. I replaced the impeller and housing as a precaution. I also checked the the tube from the block to the guage for kinks or blockage, their is still no change in pressure on the guage. What should the guage read, and how much water pressure should the block have.

[boats.net]

The minimun pressure is 10 psi at wide open throttle, at idle it will be 0. Check for open thermostats or open pressure control valve, number 8 at http://www.boats.net/parts/search.ht...7CUPPER+CASING

Ok,I'll start with the easiest, the pressure control valve, then check temp on each side of block with heat sensor. What temp should the thormastats open? Does this engin have an overheat/low water pressure shutdown sensor or horn? Sorry for all the questios , this is my first Yahama. I ordered an owners manuel which has not arrived yet.