How to Fix an Outboard Motor Water Pump

Your outboard motor water pump is what pumps water up to the top of the motor from the lower unit. This process helps to keep your engine cool while you are using it. When mud, sand and shells get into your outboard motor water pump, they will keep your water pump from operating properly. Left unchecked, this debris can cause enough damage to your water pump that you may need to replace it. Yet, the life expectancy of the water pump on your outboard can be maximized by performing minor repairs on it as necessary.

Difficulty:

Moderately Challenging

Instructions

1. Remove the bolts on your lower unit (just below the anti-cavitation plate) using a 12 to 14 millimeter wrench. The make of your outboard motor will determine which size wrench you need to use. All the bolts should be the same size.

2. Take the trim tab (anode) off the bottom of the anti-cavitation plate. You will find the tab right above the propeller. The tab's position on most outboards will be bolted through the bottom of the trim tab. Keep the tab and the bolt separated after you remove them.

3. 

   Remove the last bolt from the lower unit. This will actually detach the lower unit from the motor. Handle this step cautiously to avoid having your lower unit slide out uncontrollably. The lower unit should be entirely free from the motor after you perform this step.

4. Place the lower unit that you removed in Step 3 aside in a safe place. The motor and shift shafts will be exposed once the lower unit is removed. Proceed with removing the motor and shift shafts by applying gentle pressure and sliding them out.

5. 

   Take the bolts off the plastic casing that houses the water pump. Handle the bolts with care to minimize breakage due to corrosion. You should easily be able to lift the casing off of the water pump once you have removed these bolts.

6. 

   Slide the pump impeller over the motor shaft. Remove the steel plate along with the gasket that the impeller was on.

7. Take the stainless steel cup and "o" ring out of the plastic casing that you previously removed. Also, remove the key way from the motor shaft by gently tapping it with a standard screwdriver (flathead) in a top-down motion.

8. Lay the parts of your new water pump kit out neatly in your work space. Installation of your new outboard motor water pump will take place in the exact reverse of dis-assembly. Replace the gasket for the steel plate in it's original location. Put the gasket back over the steel plate and make sure that is securely fitted over the gasket. Install the new key way. Locate the small indentation on the impeller and line it up so that it is properly placed back atop the stainless steel plate. Put the new "o" ring around the outside edge of the cap. Set the new stainless cup in place inside the plastic casing. Slide the stainless cup and "o" ring over the motor shaft to the impeller. Turn the motor shaft clockwise while pressing down on the plastic cap. Grease the bolts that secured the plastic casing and replace them.

9. Grease the tops of both the motor and shift shafts. Grease and replace the bolts.

10. Reinstall the lower unit by finding the two holes in the mid-section of the motor. Line the shafts up to the holes and insert.

Resources

• Read this Article in Spanish
• The Outboard Motor Handbook
• 9.8 Horsepower Four-Stroke Outboard Motor
• Outboard Motors Maintenance And Repair Manual
• NBOA Marine Insurance
• Sierra 18-3431 Yamaha Outboard Water Pump Repair Kit