Guide to Replacing an Outboard Impeller

Your boat is your prized possession — like any other vehicle, you take good care of it. Part of owning a boat is understanding the importance of checking all parts frequently since it's constantly exposed to water and has a higher risk of corrosion and other damage. While it's good to have measures to prevent external damage, inspecting and maintaining the internal parts that keep your motor running is vital. 

One such part that should be checked routinely is the outboard impeller. When your impeller is damaged, the consequences can be severe for the rest of your motor. This guide provides steps to replace your damaged or broken impeller so you can continue enjoying your boat. 

What Is a Boat Impeller?

An impeller is a small but essential part of a boat and is found in the motor. While a propeller is located in the water and creates the force that pushes the boat forward, the impeller draws water into the water pump to increase the pressure in the motor. This aims to keep the engine cool while it's running. 

An impeller is made of rubber to assist with lubrication. It is fairly durable but must be handled carefully and should ideally be replaced after approximately every 200 hours of use. The physical composition of an impeller includes a round core with six or more vanes or fins attached to it. It is located next to the water intake and drive shaft within a pump housing when the lower unit is disassembled.

Signs of a Damaged or Broken Impeller

One of the first signs that the impeller is broken or damaged is your motor overheating. Turn it off when you see something's wrong, then wait for it to cool down before inspecting it. Other issues could cause overheating, but the impeller is most likely the culprit due to its limited life span and tendency to break under consistent and immense pressure.

The main cause of an impeller breaking is running dry, as it must always be well-lubricated. Harmful particles and other debris getting sucked in with the water is another reason it often breaks. If the boat stands stationary for months, it could also lead to the impeller drying up and becoming brittle — always check the impeller at the onset of the new season before regular use.

Physically, a damaged or broken impeller will have missing vanes or fins on the core. They often break off when they run dry, or debris erodes them at high speeds. Sometimes, you'll find the vanes have fallen into the water intake, which can cause severe damage to the system. If you notice fine lines or cracks in the individual vanes, they are damaged and should be replaced.

Step-by-Step Instructions on How to Replace an Outboard Impeller

Replacing a boat impeller requires numerous steps, which we've listed below. Remember that these extensive steps guide you on everything after you've removed the lowering unit, not before.

1. Disconnect the shift rod using a small screwdriver to remove the screws holding it. You'll notice a black piece of plastic that you can remove.
2. Using two wrenches on either side, break the nuts by spinning them off. This separates the shift rod entirely from the lower unit.
3. Remove the two remaining bolts with a ratchet or extension.
4. The lower unit will drop once the bolts are removed. Shake it gently if it's stuck.
5. Remove the long nut off the shift rod, which will free the lowering unit.
6. Next, break free all four bolts around the water pump housing, including the bolt that has a black grommet. Be careful not to remove the shift rod by loosening the single bolt next to the rod.
7. To inspect the water pump, rotate the drive shaft by taking it out of gear and putting the shift rod in neutral.
8. Wiggle the water pump housing until you can remove the gasket.
9. Inspect the gasket, water pump housing and bell housing for damage.
10. The impeller is beneath the gasket. Remove and inspect it. If the fins surrounding the round rubber piece are missing, the impeller is broken and must be replaced.
11. If the fins fall into your intake screen, remove them immediately, as well as any fine pieces that may have broken off. Failure to remove broken pieces will block the water flow in the system.
12. Ensure the small metal impeller key is in place, as this vital piece prevents the impeller from spinning around the dry shaft. While replacing the boat impeller, put the key aside safely for when you need it later.
13. Inspect the intake and cover it with a new gasket.
14. To install the new impeller, grease the impeller key and place it back into position right beside the drive shaft.
15. Slide the new impeller down the drive shaft until the fin indent fits perfectly into the key, and apply pressure to secure it.
16. Then, slide the impeller and water pump housing on top of the impeller.
17. Use soapy water as a lubricant to prevent damaging the new impeller, and slowly rotate the driveshaft as you press the water pump housing down onto the impeller.
18. Tighten the four bolts you initially removed using a ratchet to secure the water pump housing again.
19. Grease or lubricate the small black rubber grommet to make sliding over the water pump pipe easier.
20. Finally, reinstall the lower unit onto the motor by lining the drive shaft and shift rods accordingly.

It's important to note that various boat and impeller brands are available, so these steps may vary between motors and serve as a general guide to identifying and replacing an impeller.

Need Help Finding or Identifying an Impeller? Speak With an Expert Today!

When you realize the importance of every component in your motor — like the impeller — you probably won't take it for granted. Whether you had prior knowledge about them or this guide has given you some new insight, it's always good to be prepared with a spare impeller if you need to replace it.

That's where Fawcett Boat Supplies steps in. We are one of the most reputable boat part suppliers. With over 75 years of experience, we are confident in our ability to deliver the best service using the highest-quality parts available. We often deal with Yamaha impeller replacement and Jabsco impeller replacement since they are two popular brands, but we also offer impellers for other brands. If you need help with outboard impeller replacement or other boat parts, call us at (410) 267-8681 today to speak to an expert or complete a request form with your inquiry.