Checked your impellers lately?

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Tom

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Jan 13, 2005
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48,526
Boats with "fresh water cooling" systems rely on one or more sea water pumps to pump 'raw' water through various cooling system components/heat exchangers. We have 3 such pumps (2 engines and generator).

Our 3196 big CATs were in need of service, and we caught the (4" x 3.5") impellers in the main sea water pumps in time. The first two photos show a 'used' impeller (1 of 2) that I had on board for emergency use; You can see the slight 'set' that it had taken, and the beginning of a tear in one fin. The other two photos show what came out of the pumps this time around; Serious 'sets' and pieces of impeller missing.

I haven't seen them gone this far in the years we've owned the boat. Surprisingly, they still moved a lot of water when the engines were fired up before replacing the impellers.
 

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SargeW

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Dec 12, 2008
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Where ever we park it!
Wow Tom, that's amazing. I do need to have my outdrive checked for impeller wear, it's just been a ways down on the list of stuff to do around here. I did have one fail in a previous boat while under way. The resulting overheating cracked both manifolds and resulted in being towed by a friendly boater back to the dock. Not an experience I want to repeat.
 

phil-t

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Jul 10, 2017
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824
Location
Ogdensburg, NY
My fishing boat is not any big ship but it still requires that pump and impeller for cooling. I replace mine every spring b4 fishing/boating season starts. Sometimes I find it in need of replacement and sometimes not - it gets replaced anyways.
 

Tom

Administrator
Joined
Jan 13, 2005
Posts
48,526
The location of the port sea water pump is outboard of the engine. I've never been able to crawl between that engine and the hull, and always have to rely on a skinny and nible mechanic or relative to change the outboard impeller and outboard zincs (both sides). I usually have to stand by in case they can't get out (I have to drag them out by their feet/ankles).

I can usually get to the generator impeller, but have to reach behind the generator, bend my hand 180 degrees, and work blind. I always hope I don't drop one of the small screws securing the cover.
 
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