Broken Salt Water Pump Impeller

[Sedna]

I have twin 7.4 MPI MIE Mercruisers. One of the raw water pump impeller vanes about 1/2 long and 1/4 wide broke off and is I think in the water system. The pump pushes the water to the trans cooler first then the oil cooler them into the heat exchanger. Since the trans. cooler has a strainer inside and it is the first location and I didn't find it there could it have gotten ground up before it got out of the pump and will pass through the system or do I have to go through the system?

 

[fwebster]

A brittle broken off impeller blade can bounce around in the turbulent water flow and eventually get beaten up into small enough pieces that it will pass thru the system. Be sure it isn't caught in the system somewhere....inspect each heat exchanger/cooler and use a hose to black-flow them if needed to be sure.

You have just figured out why it is easier to replace the impellers on a regular basis.......diving for blades isn't fun and can be very time consuming.

 

[Sedna]

Thanks you are absolutley correct I found it in the out port of the sea water pump -- just lucky after I already took the cooler section apart. how often should they be replaced

 

[fwebster]

I don't know what Mercruiser says, but most careful owners in our area consider the impeller change to be part of their annual service, but we are in a warm area where people use their boats 12 months/year so 150 hours a season isn't unusual.

It doesn't take but one SeaTow trip and hunting for broken impeller vanes in the seawater side of the cooling system to offset the added cost of a frequent impeller change.