Changing an Impeller


Every 2-stroke outboard (since the extinction of the air-cooled outboard) requires water to cool it. There is a waterpump that is bolted on top of the driveshaft. Generally, the waterpump is held down by 4 bolts. Inside of the waterpump, there’s a rubber wheel called an impeller. Many people make the mistake of ordering a waterpump kit, which would include both the waterpump and the impeller, when in reality, they only need an impeller. The only time you need to replace a waterpump is if the existing one is damaged in some way.

Impellers should be changed, at a minimum, every 3 years. This is my common sense approach. Manufacturers recommend different times for different outboards and I’ve even heard of recommendations to change them as often as once per year. In my opinion, that’s a ridiculous notion that’s for little more than the sake of drumming up business. I’ve had folks come in for an impeller change on an engine that’s been in use for 20 years and the impeller still looked like new. While I do not recommend a 20 year wait, an annual change is rarely necessary.

Changing an impeller is simple enough work. It doesn’t take any special tools and it can generally be accomplished in about 30 minutes. Added to changing the lower unit oil, I’ve seen marine businesses charging as much as 2 hours labor for this job, which could run you as much as 200 to 250 dollars in parts and labor. This is an unnecessary waste of good money, I think, for something that’s easily enough accomplished at home.

What you need:

  • A new impeller-ensure that you are getting an OEM or quality aftermarket replacement. Sierra impellers are good aftermarket replacements, as are Mallory and probably a few others.
  • Tools to remove the lower unit from the midsection-Generally, a box wrench set will accomplish this but occasionally, another hand tool is necessary. You won’t need anything more exotic than an allen wrench or a screwdriver, so don’t get excited.
  • A ratchet set-This is for the removal of the waterpump itself.
  • ***Suggested***Most manufacturers recommend greasing the driveshaft when servicing the impeller. Some people grease them and some don’t. If you’re in saltwater regularly, I’d recommend using a quality marine grease on the driveshaft but otherwise, I don’t consider it a big issue.

What to do:

  1. Remove the lower unit. Mercury, Yamaha, and Suzuki outboards will remove as soon as you remove the bolts holding the lower unit to the midsection. Johnson, Evinrude, some Suzuki, and older Force outboards will require you to disconnect the shift rod. On the older Force engines, the shift rod connects behind the midsection, and can usually be separated by a piece of linkage there. The Johnson and Evinrude outboards are usually disconnected under the carburetors. With some of these newer Johnson and Evinrude engines, you’ll need to remove another part in order to access the shift rod. Every engine is a little different. Remember that when in doubt, there should be an excellent primer on lower unit removal in a good service manual.
  2. If you follow the driveshaft down, there’s a waterpump cover at the base of the driveshaft. It will have 4 bolts holding it to the lower unit housing. Once you remove these 4 bolts, the impeller can be accessed. Be careful here to note whether or not there is a driveshaft key that the impeller is sitting on. Don’t lose that key.