Changed impeller. Doesn't overheat now. Have a question.

[hz293]

Mercruiser 5.0, Alpha 1 Gen1 1989. After pulling lower unit, changing impeller and putting it on muffs, the overheating problem I was having seemed to go away. After a short time the engine reached about 160 or so and then I heard a shift in engine pitch and it went down to about 140 or so. Each time it started up again, not to 160 though, I heard a change of pitch and back down it went. I'm really happy but I'm curious if this is normal and what makes it happen. Just want to make sure before I put it back in the water and go away from land.

 

[Scott Danforth]

not sure what you are hearing in pitch, however the cycling back and forth on the gauge is your thermostat opening and closing.

by any chance was your impeller missing pieces? if so, you could be hearing the water trying to rush past the missing pieces in one of the fittings.

 

[hz293]

Thanks for getting back. I can tell the that the gauge is cycling as the thermostat opens and closes but there is definitely a change in engine pitch also. I'll look for the RPM's next time to see if it changes. I'm sure happy that the impeller change made the difference. The impeller that was in it still had some elasticity to the rubber but the vanes had a set to them. There was no pieces missing.

 

[thumpar]

If you are doing this on muffs it is hard to say. Put it in the water and see what it does.