Impeller: Why You Need To Check It!

Here’s a quick little blog for you that is one of those hidden issues when it comes to outboard motors. Whether putting your boat away for winter storage or prepping it for the upcoming fishing season, proper maintenance is crucial. In this case, it’s usually in that spring prep time that the damaged item I’m about to talk about rears it’s ugly head (and that’s why fall is the perfect time to investigate the following). The item is called an impeller and it is vital to help maintain a constant, safe motor/engine running temperature for your motor to not only work properly but not to be destroyed!

An impeller in an outboard motor is quite simply, the main component to your water pump. It spins at a fast rate of speed, pulling H2O from the body of water you are in, and pumping it up to and into the powerhead.

The impeller is made of rubber which means, it can and will deteriorate through time. A bad impeller is a recipe for disaster.

The reason I called it a hidden issue is during a “spring tune-up”, typically it isn’t checked unless you specify. Normally the mechanic is busy changing filters, spark plugs, etc., all up at the powerhead. The impeller is located in the lower unit. The reason you need to request your mechanic looks into it is because of all the labour time to look at it (if they checked it out and the impeller was good, one could argue that that ½ or higher hour labour was expensive and unnecessary).

It’s a good idea to check or have someone check your motors impeller every 3 years.

Once all is checked, fixed, replaced, prepped and ready to go, it’s time to put your ultimate fishing machine in the water and start fishin’!

3 Replies to “Impeller: Why You Need To Check It!”

  1. You can always tune-a-motor, but you can’t tuna fish. At least I don’t think you can. The good, bad and ugly-ness of literally gutting your outboard motor isn’t for the faint of heart.

    The impeller itself is simply a series of rubber vanes molded around a hub. The vanes are flexible, and the hub rotates on an eccentric within the pump housing, which has a stainless steel liner. The tips of the impeller vanes can wear out from simple use, but if the motor is often run in silty or sandy conditions, this abrasive material can accelerate impeller wear. The rubber material can also get stiff and brittle, a common problem on motors that sit unused for several seasons. Then the vanes can “take a set” in one position and not flex back. The other impeller-killer is heat. Water lubricates the pump, and if it’s run dry the impeller can be ruined in just seconds.

    The most-common cause of impeller failure I see is simply old age. Many marine technicians find a lot of the impellers that are too worn at the tips to pump well, or are really stiff. If possible, make changing the impeller part of your off-season lay-up program, because if it fails you can have much more expensive problems.

    When the impeller fails, the pump can’t pump and the engine will overheat. Mechanics have reported about old outboards that got so hot the paint burned off the power head. Most newer motors have a warning horn that sounds when the motor gets over heated, and a program that cuts engine r.p.m. to try and protect the power head. If they are running wide-open, by the time they hear that horn and react, they have a scuffed piston, especially if it’s a two-stroke motor. And even if the motor is OK, now they are out in the middle of the lake and the day is shot, at the very least.

    A ruined impeller can also be caused by running aground. You can suck a lot of abrasive trash into the pump if you run the gear case into a sand bar. There have been cases where the water intakes were just packed to the point where water could not even get to the pump. If you get in that situation, it’s a good idea to have the impeller checked just as a precaution.

    Warning : Starting the engine “dry,” that is, with no water supply to the pump, is instant death to the impeller. Boat owners who give the motor a quick bump with the starter on the launch ramp, just to make sure it’s ready to go when they get in the water, and others who think they need to start the motor after pulling the boat out of the water to drain it – both are big mistakes that will ruin the impeller.

    Another issue is owners think they can start the motor if a hose is hooked up to the flush port. That pushes water through the power head and exhaust, but very little gets to the pump. Mechanics tell owners to always use a set of water muffs on the gear case if they want to start the motor with the boat on a trailer.

    When an impeller fails dramatically, simply installing new parts may not be the end of your trouble. If the impeller really comes apart, there’s a good chance that little bits of rubber can get lodged in the water tube and restrict flow to the power head. You might notice a weak stream from the water pilot out the side of the motor, and that could mean that the technician did not check for impeller debris. If that’s uncorrected, the motor could overheat.

    As Angelo has stated, “The reason you need to request your mechanic looks into it, is because of all the labour time to look at it (if they checked it out and the impeller was good, one could argue that that ½ or higher hour labour was expensive and unnecessary).”

    “You People” have been warned . Replace that impeller every three years or sooner. Any way you look at it, this little rubbery thingy could put your life in jeopardy if and when a catastrophic failure occurs out on the water.

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