Hi all<br /><br />I have 1979 Mercury 50. (4 Cylinder), whichs runs great and has good compression.<br />The water pump was changed a couple of seasons ago (about 10 trips) in saltwater.<br />The other day I took the boat out and ran it for 10 minutes into the bay at between<br />4000-5000 RPM and stopped ready to anchor. The water pressure gauge was running at <br />between 5-6 PSI at 5000. when it was idling, the water from the telltale was quite<br />hot (But not too hot to hold my hand under it), and there was a small amount of steam<br />from the 2 exhaust holes under the cowling. After 2 minutes of idle, the steam stopped<br />and water returned to just warm. My initial thought was failing pump or blockage (under high revs), but then I figured that after a 10 minute run at high revs, and a sudden stop, the motor should be hot and as the impeller slowed to idle, the blades would have flattened out<br />and provided more water for cooling. Does it sound like the impeller is due for a change ?
