Water Pump Repair: Cheap is a Mistake

Impeller housing

In this diagram you can see the rib that supports the impeller as it crosses over the intake port. What we didn’t know is that the rib had broken on our housing, which trashed the new impeller in just a few days.

Sooner or later, you’ll find yourself down in the bilge of  boat, repairing a shredded water pump impeller. Then, a couple of days later, you could find yourself back in the bilge, fixing it again.

Not long after I bought a spiffy new-to-me boat — also known as used —we were on a road trip, boating on different lakes, when the overheat alarm sounded. After we limped it back onto the trailer, we figured out the impeller had gone bad, which, given the hours on the engine, made sense.

I pulled it apart. The Bravo One drive uses a belt-driven pump to draw water up from the pickups in the lower gear case and up into the motor, but it’s largely the same impeller design as an Alpha drive. The impeller in the Alpha drive is driven off the main vertical shaft, but it fails in the same manner as the Bravo impeller. The rubber gets hard and brittle, and biased in the direction of rotation, at which point it either, a) fails to draw water, or b) disintegrates into chunks you have to find and fish out of the cooling system.

Naturally, ours disintegrated, so I had to pull off all the cooler hoses to find all the missing pieces, which can clog coolers and lead to other problems.

Impeller kit

Save yourself the headaches and buy the whole body and impeller kit from MerCruiser. Most late model Mercs take Part No. 46-807151A14.

When I was at the marine store, I had a choice. I could buy the impeller and housing, or buy just the impeller. Our housing didn’t look bad, so I bought the impeller and saved myself $60, which I could spend on something else. Like beer. That would become false economy.

Turns out the rib in the black plastic housing that supports the impeller as it crosses over the water intake side had broken off, but I didn’t notice that. So, when the new impeller would cross the water intake opening, it would catch on the remnants of the rib, which shredded it in a couple of days.

When I was trying to flush the unit with the “muffs” over the lower gear case, it wouldn’t draw water. That meant I had to remove the water pump again — which is no picnic — and buy a new impeller and housing. Long story short, my penny pinching cost me more in the long run.

The moral of the story is, at least when it comes to Bravo drive water pump repairs, sometimes cheap is too cheap. Buy the impeller and housing, and consider that the extra expense goes toward peace of mind. And that especially applies to a boat you just bought, because the guy who just sold it might have gone cheap.



  1. John Rains says:

    In industry, we always feel the inside casing surface of any rotary pump where contact (or very close clearance) is made between the impeller and casing, e.g. sliding vane pumps, gear pumps, etc.

    Be sure to wear gloves as small metal slivers can create really bad cuts and finger tips are full of nerve endings and blood vessels. But if you use a piece of material similar to pantyhose material, it will alert you to any roughness or sharp edges, even with the gloves on.

    However, it is all relative and your suggestion to replace the housing has merit unless you are sure you know the age of the pump and check the condition of the inside surface.

  2. Fitz says:

    Hi Brett,
    I can’t count how many times I have taken our family boat out onto the lake, only to have to bring it back into the trailer moments later because of some broken or overheated part. From reading your article, I don’t think we have ever had any particular issues with the impeller, though it does sound like it would be important to have the highest quality parts possible when dealing with the inside of the prop.

    I love boats, and being outdoors with the family. I think it’s always important to use good quality products, and test the boat before taking it out to launch, though many problems with the boat are unavoidable. Thanks for sharing your story of the “new-to-you” boat, and good luck in the future with it all!