Yamaha 6, No Water Flow, Impeller ~OK

I bought a used Yam 6 (with the sail boat) It rarely gets used for more than an hour and allmost never above 1/2 Throttle.<br /><br />In any event I do not get a stream of water from the outlet. I had the water pump apart last year and agiin this spring and still looks OK, the impeller is intact and fits in the "cup" snug, no other damage. <br /><br />Is there any way to ensure the pluming throught the powerhead is OK? I tried to push water through via the tube that goes into the pump, using a labrotory type squeeze bottle, but no luck.<br /><br />I see that there is a thermostat so I assume this is closed at this time, is it possible that the termo is never opening up?<br /><br />I also see that the water pressure can be measured in some engines, I can not find any thing on this for the 6 in the manual I have. Any suggestions.