Is there water spitting out the back? If there is none, check the water pump impeller. Also, I've had problems with my water strainer (Perko?) lid not sealing tighly and letting air into the system.
If there is very little or no water, check the fitting where the water goes into the exhaust elbow (a cast upside down U shaped pipe). The fitting I have bends 90 degrees and has clogged twice over the last 8 years. The first time I had to replace the exhaust elbow, the next time I managed to clean the fitting out with a stiff wire.
Ed Austin
Chinook
