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.



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