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Compass Marine How To | all galleries >> Compass Marine How To Articles >> Changing A Raw Water Pump Impeller > The Raw Water Pump
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The Raw Water Pump
23-JUL-2008

The Raw Water Pump

Changing an impeller is not a daunting task and it's one that every boater should consider adding to their arsenal of DIY maintenance. Changing and impeller, on many engines, usually takes less than 20 minutes even if you are fairly slow. The most complicated aspect of it is access to the pump.


Impellers are a wear item unfortunately they do not always abide by a "time" or "hours of use" schedule. A simple mishap like forgetting to open the engines raw water intake can kill an impeller in short order. They don't like to be run dry and they don't like heat. If let go for to long they can "throw" a blade or loose a chunk that can lodge in the hose or the heat exchanger. If this happens you have a much larger job on your hands of finding the piece to prevent further damage or overheating issues.


I change my impeller every year regardless of condition. Some feel this is overkill and you'll need to decide for your self what you maintenance schedule is. I look at it this way, impellers are cheap insurance! I pay $16.00 for the impeller used in my Westerbeke diesel engine and it takes about 8-10 minutes to change it. It took me twenty minutes even while photographing it and the access for my large camera was very tough!


An over heated engine or a thrown blade can cost many, many times more in both time and money than the few minutes and the "low" boat bucks required of this simple maintenance. Heck, changing an impeller costs less than changing my engine oil and filter.. If you do it every spring, or every time you run it dry for more than a 30-45 second period, or under restricted flow due to a blockage in the strainer or intake system you should have a trouble free impeller and never throw a blade or lose flow due to a worn impeller again.

Nikon D200
1/60s f/4.0 at 24.0mm iso100 full exif

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David Bartilson 26-Aug-2014 17:25
Correction: My previous post indicated difficulty changing impellor. That task is not nearly as bad as trying to remove/replace the pump. There are 2 bolts on mine Westerbeke W30, that attach the pump to a slide that adjust tension on the belt. Those 2 bolts are a BITCH!
David Bartilson 26-Aug-2014 15:59
Changing the impellor on my CS36T, Westerbeke W30 is a daunting task! Not intellectually but physically. Reaching the bolts and the length of swing is so limited that only about an 1/8 of a turn can be made each time the wrench is engaged. Stubby wrenches and perhaps a ratcheting box end wrench will make it easier. However, replacing my impellor yearly will be on my maintenance list!
Jeffrey Orling 08-Jun-2012 00:16
YIKES.. I was wrong... checked my log and the average annual engine hrs ove last 10 yers was only 108! just over 4 continuous days.
Jeffrey Orling 08-Jun-2012 00:03
Nothing wrong with anual maintenance but I am wondering how this is keyed to engine hrs? I typically run the engine less than 200 rs a year and that only 8 continuous days and that seems on the face to be a very short service schedule. What say you?