Do You Know How to Flush Your Outboard Motor?

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An essential part of owning and operating a boat is flushing your outboard motor. That is especially the case if you regularly run it in saltwater. Untreated salt buildup and corrosion can keep you off the water. Worse, the servicing to combat them can cost more than you might be comfortable with. So do you know how to flush your outboard motor?

Flushing the motor keeps it clean, protects the internal components, and ultimately extends the motor’s life. If you’re running your boat on saltwater, you should really give your motor a full flush after every use. You should flush it every six months while it sits in storage.

The Classic Method

Fortunately, the process to flush your outboard motor is fairly simple and doesn’t take very long or require many tools. To effectively flush your outboard, you basically need three things:

1. A garden hose
2. Salt-free running water (from the hose)
3. Flush muffs

Resembling an oversized set of earmuffs, flush muffs are surely the most common tool used to flush an outboard. You can buy a set for less than $10.

Connect your hose and fit the muffs over the engine’s water intakes on the sides of the gearcase. The muffs should completely cover the inlets, so make sure they don’t loosen or slide off when the water starts running. Also, confirm there aren’t any additional water intakes that are not being fed water by the flushing muffs. If there are, seal them off before you begin flushing to avoid overheating. Duct tape—is anyone surprised by this?—will usually do the trick.

Note: If your engine doesn’t have water intakes on the sides of the gearcase, you’ll likely need to substitute a special aftermarket attachment for the flush muffs.

Flushing Bag Method

Are you not a fan of listening to your motor’s open exhaust during the flushing process? Have neighbors complained about the process’s noise? Then a flushing bag could be a preferred method.

Just like a set of flush muffs, a flushing bag is accompanied by only a garden hose and running water. These soft-sided bags made of vinyl or heavy plastic use a supported framework to fit snugly around the bottom of the engine. When choosing a flushing bag, though, ensure you get one that reaches well above the water intakes.

Time to Flush

Now you’re ready to flush your outboard. Attach the hose to your muffs or flushing bag and turn on the water. Maintain enough pressure that water wants to squirt through the sides of your chosen attachment. Start the engine and let it run in neutral. The water should be coming out of the tell-tale, which means it’s running through the entire powerhead. If no water emerges from the tell-tale, kill the engine immediately to prevent any overheating.

Once your engine is running and water is effectively pumping through and flushing out buildup and debris, you need to stay nearby. You want to be close enough to immediately stop the process in case of trouble, to avoid any serious damage. Ideally, your idle speed should not exceed 1,000 rpm.

Let the motor run until water starts running from the thermostat relief. Then, let it run for an additional five minutes before turning off the motor first, and then the hose.

Common Mistakes to Avoid

While it is a quick and simple process, flushing an outboard can go wrong in a hurry with even a minor miscalculation. Let’s review things not to do:

• Don’t skip the flush after a saltwater trip. This is unquestionably the most common mistake boaters make. Saltwater is an adversary to boats. It simply destroys whatever it touches if ignored. Do yourself a favor and make it a habit to flush your motor every time you use it in saltwater.

• Don’t run the engine without water. An outboard needs water to run, let alone flush. Water is crucial for cooling the engine, as it flows through the cooling system to keep engine components at a safe temperature. If you flush it without using water, you could cause serious damage in less than a minute.

• Don’t rev the engine while flushing. This is one of the most classic rookie mistakes when it comes time to flush your outboard. Revving the engine doesn’t flush the motor any better or faster. Flushing should be a gentle cleaning process, and revving the engine can cause serious damage.

• Don’t use water with high mineral content. Hard water can lead to mineral buildup in the outboard’s cooling system. Calcium, magnesium, and other minerals can accumulate over time and lead to all kinds of long-term problems.

You don’t have to be mechanically inclined or talented to flush your outboard motor. You don’t even have to like doing it. But you do have to do it. At least if you want your outboard to last as long as it should and provide as much on-the-water time as you expect.

David Schlake

Hailing from Goochland, Virginia, David grew up on the James River with the Atlantic Coast less than two hours away. While his proximity to prime waters resulted in a passion for both freshwater and saltwater fishing, he also enjoys upland and big-game hunting. He graduated from West Virginia University with a degree in journalism before making his way to Austin, Texas, in 2016.

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