Filed Under (Boat/Trailer Maintenance) by Debbie on 29-08-2007

Every boater, sail or power will eventually be faced with “the case of the limping impeller”.  It doesn’t matter if your marine engine is a small outboard or a large inboard, if the water isn’t spurting out the back, bottom, top or somewhere it’s supposed to…you’re in trouble!  In my post about buying a used boat the very first item you should do is change the impeller.  It’s an important thing as it can make or break your boating experience (see Water’s Important for Boats).


I realize that not everyone is a hands-on type but my hubby and I are and I’ve been covered more than a few times in engine oil…  Although this is a good thing ladies, you see I frequently captain our boats alone and I need to be self-sufficient (although a cell phone can come in handy for those ‘hubby how to fix it’ calls).  So a basic understanding is important as an on the water service call can be pretty spendy or even impossible to get!


Flexible impellers can flake off small pieces that can and do move through your engine, find places to ‘stick’ and cause additional problems later so it’s important to keep on top of this.  It’s not so high tech as to require lots of smarts but the right tools can really make life easier.  We keep a spare impeller and an impeller puller on board at all times.


The main cause of problems with your impeller are running dry…you’re not starting the boat before it’s in the water are you?  Swollen impellers caused by chemicals usually oil or diesel in the raw water.  But sometimes too it’s just plain old age.Flexible Impeller




So here’s how we change out our flexible impeller.



 Where to find impeller pump on Universal Diesel














ü      Remove pump cover by removing the screws.  Be sure to have a cup holder or something to put all of them in.  They are small and boats rock with the waves and wakes and it’s no fun to loose them!

ü      Remove old gasket from pump cover and throw into garbage bag.

ü      Place impeller puller over impeller and attach ‘fingers’ to back of impeller and pull old impeller out and toss into garbage, in a pinch (no pun intended) you can try a pair of needle-nose pliers.  (Some impellers are sealed to the shaft with O-rings; most aren’t.  If it won’t come out, it may be locked with a setscrew or Allen screw…Volvo and Atomic Four’s in particular.  Sometimes you can pull the impeller out enough to release the screw.  If you can’t you may need to disassemble the drive side of the impeller and knock it out on its shaft.)

ü      Open new impeller package, be sure not to loose the new gasket.  Find someplace safe to place it so it doesn’t blow around or out.  Treat it gently.

ü      Slide new impeller over pump shaft.  You may need to lightly lubricate the impeller with dishwashing soap and push in all the way in.  Bend the vanes in the opposite direction to rotation if possible.

ü      Replace the gasket be careful some are very, very thin.

ü      Replace pump cover and screw back in place.

ü      Start engine.

ü      Check for leaks at the pump cover.


Congratulations!  You’ve just changed your impeller and saved yourself some money too.  Hopefully this helps you.  If not talk with your local marine engine guy/gal for additional help. 

1 Comment posted on "How To Change a Flexible Impeller"
Water impeller for boats on May 25th, 2008 at 6:12 pm #

[…] check your boat’s water impeller to see if you need a new one and as far as the trailer goes? Well I guess you need to read the post […]

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