Outboard Marine Water Pump

Note: This is not an exhaustive guide to replacing a marine water pump. Always consult your boat's instruction manual or the manufacturer for model-specific instructions.

The engine water pump is a crucial component of any outboard, but most people can't remember the last time they had their water pump serviced or even replaced. And if that's the case, it's probably time to replace it. Marine engine cooling pumps and water pump impellers help to extend the life of your outboard boat's engine. But, if you're using a damaged or worn out water pump, it can result in costly repairs. We're taking a look at how to tell if a water pump is bad and how to replace it with a new one when the time comes.

How to Tell if a Water Pump Is Bad

The engine water pump impeller is typically the most common cause of water circulation and overheating issues. This small, round disc has spinning blades that help to move water throughout the circuit of the outboard motor. When it's broken, the supply of water stops, resulting in an overheated engine.


  1. The outboard motor is overheating.
  2. The impeller is living on borrowed time.
  3. There is a reduced stream of water from the cooling water outlet.
  1. The Outboard Motor Is Overheating: Whenever your outboard motor's water temperature is rising, there is cause for concern. And if the motor can't produce a steady stream of water once it's reached its correct operating temperature, the impeller is the most common of two potential causes, and it's most likely heavily worn or damaged. The second cause, while rare, is wasps — they sometimes like to burrow in the cooling water outlet over the winter.
  2. The Impeller Is Living on Borrowed Time: Always inspect your impeller when you prepare your boat engine water pump each spring. Your marine engine water pump's impeller has a service life of about 300 operating hours or three years, whichever comes first. If you haven't changed the impeller in so many years or operating hours, it's time.
  3. There Is a Reduced Stream of Water From the Cooling Water Outlet: If it's your first outing of the season and you're noticing a smaller stream of water coming from the cooling water outlet, it's possible it could once again be wasps. To rule this out, gently insert a thin wire into the outlet to feel around. If it's not your first outing of the season and you're noticing a reduced stream of water, you probably have a damaged pump housing or impeller.

How to Replace an Outboard Water Pump

Outboard motors are more reliable than ever before. However, just like any motor, parts and components will require replacing on a regular basis. It's recommended that you inspect your marine water pump impeller once a year or every 100 operating hours, whichever comes first. The model-specific maintenance schedule for your outboard water pump can be found in your operator's manual. By regularly inspecting and checking your raw water pump, you'll be better able to tell when something is amiss or needs replacing.

How to Remove and Replace an Old Engine Water Pump:

  1. Shift the Motor Into Reverse: First, shift your motor into reverse gear.
  2. Remove the Bolts & Disconnect the Shift Rod: Next, you'll want to remove the mounting bolts that secure the lower unit to the midsection, as well as any bolts under the trim tab. It's a good idea to mark the position of the bolts prior to removing them so you can position them correctly during reinstallation.
    Then, disconnect the shift rod. It's important to note that not all shift rods disconnect in the same way. Some disconnect below the swivel bracket, some by the powerhead and others above the gearcase. Refer to your instruction manual for product-specific directions.
  3. Remove the Lower Unit and Bolts: Once the shift rod is removed, you'll want to take out the lower unit and the bolts on the water pump housing. Again, mark the position of the bolts prior to removing them.
  4. Remove the Water Pump Housing and Impeller: Now, you can easily remove the engine water pump housing and impeller from the gearcasing. At this point, you can also remove the wear plate and gaskets from the gearcase.
  5. Install the New Marine Water Pump Plate and Gaskets: Carefully read over the instructions for installing your new water pump. Then, install the marine engine water pump wear plate and gaskets on the gearcase. Be sure you're using a proper sealer on the gaskets to reduce the chance of leaks.
  6. Lubricate: Once in place, you can lubricate the impeller cup, keyway and driveshaft.
  7. Install the Impeller: Next, install the impeller so it lines up with the impeller key. The impeller is usually pushed into the housing liner with a small twist clockwise.
  8. Install the Marine Water Pump Housing: Now, you'll want to install the water pump housing. Turn the driveshaft as you place the housing on top of the impeller. You'll turn the driveshaft clockwise for most standard rotation models. Then, tighten the housing bolts in a crisscross pattern to ensure a tight gasket seal. Place your new water tube seal in the water pump housing. Then, line up the driveshaft, water tube and shift rod all while installing the lower unit. Take care to not overtighten the housing's mounting screws.
  9. Lubricate and Reassemble: Now, you'll want to lubricate and reinstall the bolts that attach the lower unit to the midsection. Keep in mind that you may need to connect the shift rod prior to bolting up the lower unit.
  10. Run the Motor: Finally, run the motor and flush it to ensure the stream of water is constant. If it is, you're all set and good to go!

Keep Your Outboard Engine in Peak Operating Condition With the Help of Boat & RV Accessories

At Boat & RV Accessories, we take pride in providing customers with the best selection of marine engine cooling pumps, water pump impellers and more. It's important to keep your engine running right with high-quality parts and accessories you can count on. From Johnson Pump marine water pumps to JMP Marine impellers, you'll find the products you need from the brands you trust only at Boat & RV Accessories. Need help finding the right product for your watercraft? Reach out to us today!

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