How To Replace Your Outboard Water Pump In 10 Steps

November 16, 2021

The motor water pump is a critical component of your outboard, but most boat owners have a habit of neglecting it in favor of what they view as more pressing matters. Outboard water pumps may be simple in design, but they are also vitally important for the health and safety of your boat. It’s recommended that you replace your outboard motor water pump once a season, or at the very least, once every other season. If you can’t recall the last time you even thought about servicing your outboard water pump, it’s probably time. Marine water pumps and pump impellers help extend the life of your boat’s outboard engine, but if you’re using damaged or worn-out marine engine parts, it can result in costly repairs. In this article, we’re taking a deeper look at how to check a water pump on a boat motor — and how to replace a water pump when necessary. We’ll also provide some general tips and tricks to help you along the way.


How to Tell If Your Outboard Water Pump Is Bad

Your boat’s water pump impeller is the most common cause of a bad outboard water pump. This generally manifests itself through bad water circulation and overheating issues. The small round disk has spinning blades that help move water throughout the circuit of the outboard motor – when they break, the supply stops. Salt, mud, sand, sticks and other various forms of debris can take their toll on the pump impeller, housing and related components. Hence, the need to replace it once a season – as good of a boat owner as you are, these things are simply unavoidable. While regular yearly maintenance is the best practice, there may still come a time when the unexpected happens and your outboard motor water pump fails. If that happens, you need to know how to tell if your outboard water pump is bad.


  • Signs of Overheating: If you ever notice your outboard motor’s water temperature rapidly rises on more than one occasion, it could cause concern. Frequent overheating is the most common sign your outboard water pump isn’t working correctly. If the motor can’t produce a steady stream of water once you get it back down to cooler temperatures, your impeller is most likely heavily worn or damaged.
  • You Realize You Haven’t Replaced the Impeller: Always be sure to inspect your impeller when you start to prepare your boat for the water each spring. Your marine water pump’s impeller only has a service life of around 300 hours (or roughly three years). If you haven’t made an effort to replace your impeller since owning a boat, it’s definitely going to show some heavy signs of wear and tear.
  • Reduced Stream from the Cooling Water Outlet: If you take your boat out on the water for the first outing of the season and notice a smaller stream of water coming from the cooling outlet, you may be just experiencing a slight blockage. Gently inserting a thin wire into the outlet and feeling around can help determine if you had a family of wasps move in over the winter. If it’s not your first outing, you probably have a damaged impeller in need of replacement.


How to Replace A Water Pump

Outboard motor water pumps have become more reliable than ever before, but just like all marine engine parts, you’ll need to replace them regularly. A general rule of thumb is to replace outboard water pumps once every season, but you can find the model-specific maintenance schedule in your operator’s manual.

When it comes time for outboard water pump replacement, all you need to do is follow these ten steps to get the job done. Your outboard water pump has been designed for easy servicing and replacement – with a couple of hours of elbow grease, and the proper replacement parts from Diesel Pro Power, your boat will be ready to hit the water.


1. Shift Your Motor Into Reverse

First, you’ll need to shift your motor into reverse gear.


2. Remove All the Bolts & Disconnect the Shift Rod

Next, you can remove the mounting bolts that secure the lower unit of the outboard motor to the midsection and the bolts under the trim tab. When doing an outboard water pump replacement, it’s best to mark the position of the bolts before removal so you can correctly position them during reinstallation.

After the bolts are taken care of, it’s time to disconnect the shift rod. Not all shift rods detach the same way, so consult your instruction manual for product-specific methods.


3. Remove the Lower Unit and Bolts

Once you’ve got the shift rods disconnected, you’ll want to take out the lower unit and bolts of the outboard water pump housing. Again, it’s a good practice to mark their positions before removal.


4. Remove the Water Pump Housing and Impeller

Now you’re free and clear to easily remove the outboard motor water pump housing and impeller from the gear casing. You can also use this as an opportunity to remove the wear plate and gaskets from the gearcase.


5. Install Your New Marine Water Pump Plate and Gaskets

Once again, you should carefully read over your product manual to know the exact method you should use for installing your new outboard water pump. Once you have the details you need, install the outboard motor water pump plate and gaskets on the gearcase. Be critical of the sealant you use on the gaskets to reduce any chance of leakage.


6. Lubricate

Once everything is in place, you can lubricate the impeller cup, keyway and driveshaft.


7. Install the New Impeller

The next step is installing the water pump impeller replacement so it lines up with the impeller key. Impellers are typically pushed into the housing liner and given a small clockwise twist.


8. Install the Marine Water Pump Housing

Now it’s time to install the outboard water pump housing. Make sure you turn the driveshaft as you place the housing on top of the impeller. You’ll be turning the driveshaft in a clockwise rotation for most standard models. Then, tighten the housing bolts in a crisscross pattern to ensure your gaskets seal tightly. From there, you can place your new tube seal in the water pump housing. Then, line up the driveshaft, the water tube and shift rod together while reinstalling the lower unit. Be sure not to over-tighten the housing’s mounting screws.


9. Lubricate & Reinstall Bolts

You’ve almost made it. Next, you’ll need to lubricate and reinstall the bolts that attach the lower unit to the midsection. Be sure to remember that you may need to connect the shift rod before bolting up the lower unit, depending on your model.


10. Run the Motor

Finally, you can run up the motor and flush it to ensure your stream of water is steady and consistent. If it is, you’re done for the day and ready to hit the water.


Helpful Tips & Tricks for Replacing Your Outboard Motor Water Pump

When you set out to replace your outboard water pump, pay careful attention to your factory manual – we cannot stress this enough. Every outboard motor is different and may call for slight variations. But the process overall is still essentially the same, which is why we can give you some general tips that will apply to any motor.


  • Use compressed air to clear any debris from the intake passages and the top of the gearcase surrounding the pump. In general, it’s considered best practice to thoroughly clean any part you’ll be reinstalling on your outboard motor.
  • The sealants and lubricants that are best for your outboard water pump will be listed in your product manual. Don’t venture off for something a couple of bucks cheaper.
  • Use a dab of non-petroleum-based lubricant on the blades of your impeller when installing it into the housing. If you do, it’ll be pre-lubricated for a more seamless startup. It can also make compressing the blades into the housing easier.


Shop Diesel Pro Power for Outboard Water Pump Replacement Parts & Kits

If you find yourself in a situation where you need to replace your outboard motor water pump, head on over to Diesel Pro Power. We’ve got all the marine engine parts you need to get your boat up and running on the water. We carry our outboard water pump replacement kits for raw/seawater from Cummins, Detroit Diesel, John Deere, Caterpillar, Northern Lights, Westerbeke, Volvo Penta, Kohler, Yanmar, Onan, Scania and Perkins, so you’re sure to find what you need to fit your make and model. If you have any questions about our products, feel free to reach out to us. We pride ourselves on our customer service – you can contact us by phone or online after hours.


Related Articles: Marine Engine Parts

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