1989 45 classic mercury

[blairkb]

noticed when running engine on lake this week the engine was pumping water out just fine.when at a idle the water stops the engine alarm kicks in so I speeded up till water started coming out from the engine the alarm stopped. what would cause the pump not to work at idle to keep the engine from over heating

 

[corm]

Re: 1989 45 classic mercury

Hi,

A bad water pump impeller.

 

[blairkb]

Re: 1989 45 classic mercury

Why would the water pump out of the motor when speeding up and not pump at a ildle or very little at a ilde. Also should the hole pump be rebuild or just replace the impeller. thanks for the imfo kirk

 

[corm]

Re: 1989 45 classic mercury

Hi,

My thinking is that the blades are set so you do not have much pressure at low speeds. Or your body and plate are over heated and out of square. When you engine is running at high speed your impeller blades are swept back anyway so the pump turns into a slinger type pump. The pressure of the water being forced into the holes by the passing water will cool most motors. When I used to race we did not use impellers in some engines. of course the water pickups were in a better locating for those lower units than production lower units.
Anyway the pump works as a suction/pressure pump at an idle and a water slinger at RPM. I should mention that the small diameter pumps in the old Mercs were less effective than the newer big vane pumps that they use today.
While the old pumps work great the controlled temperature of the new motors require the big bladed impellers to work reliably.
I could be all wrong too.

 

[blairkb]

Re: 1989 45 classic mercury

Thanks for the imfo depending what I find by lowering the bottom unit could I replace just the impeller if thats all that looks bad or normally do you replace other issues when your down their regards to the water pump thanks kirk

 

[corm]

Re: 1989 45 classic mercury

Hi,

I usually only replace the impeller. But I don't run the engine out of the water,
in the weeds, or in the sand and muck. If any of these have been done to yours you may have to replace the body, base plate, and base. It is fairly easy to tell by looking. The body and base will melt a little. This causes the impeller to not be square in the body and will shorten it's life and possibly the pressure. If there is a deep grove wore in the stainless steel base plate I would replace it too. Some water is full of suspended silt and can cause these problems with normal useage.