How to Flush Outboard Motor on Mooring (3 Methods Discussed!)

How to flush outboard motor on mooring is a frequently asked question by boat owners. Flushing an outboard motor before and after use is essential to ensure good conditioning and prolong its lifespan.

There are various methods of flushing an outboard motor on the mooring. It could be through flushing muffs, connecting ports, or built-in flushing ports.

If you’re looking out for answers on outboards, explore more in this article.

Methods of Flushing an Outboard Motor on Mooring

Salt water-based outboards should be flushed regularly along with outboards used in lakes or rivers because there is plenty of corrosion and contaminants that can get sucked up into the motor.

Each manufacturer has detailed instructions on how to properly flush the outboard according to its component and model.

A pamphlet is given together with the purchased outboard motor. However, if you happen to throw or misplace it, asking for another copy from the owner is possible.

how to flush outboard motor on mooring

Generally, these motors usually require freshwater as a flushing material. There are outboard motors with flushing ports already to make the job easy.

So, be keen on reading and following the exact directions to avoid damage and to flush correctly. If you are not confident in doing the procedure, consult the owner for assistance.

The following information discussed begins with the common brands of outboard motors and the frequently applied methods for flushing.


When opting for flush muffs, start by purchasing heavy-duty tapes and flush muffs to cover the auxiliary water inlets.

The tapes are used for 15 to 30 hp models and light Lightning M2-type gear cases. Do not forget to remove those tapes after flushing.

Hook up the muffs making sure it fits outboard intakes. Set water pressure at least 20 to 40 psi or compare it to the manual you have.

Flush the outboard in about 5 minutes at a recommended speed. Turning the engine depends on the manual guidelines or keeping the engine in a vertical position to automatically drain water from the powerhead.


In general, flushing Honda’s outboard motors should be in a vertical position. However, the method lies in its size and model.

The recommended method for flushing motors with 2 to 20 hp engine sizes is by flushing bags, using small containers or buckets.

Engines with more than 5 hp sizes are advised to be on optional flushing connections just enough to flush through the port from the side of the gear case. Always detach the propeller before flushing and run the engine for about 5 minutes.

Midsize engines of 25 to 50 hp should only use the wash port. This can be found either in the lower or side area of the gear case. Keep in mind to remove the propeller before starting and run the engine for 5 minutes in any procedure.

Honda suggests large engines with sizes 60 up to 250 hp, to utilize the standard flushing method of attaching a garden hose to the port without running the engine.


Just like the previous brand, flushing Mercury outboards differ in sizes and units too. They offer water sports in the lower engine cowl for easy access to the garden hose adapter.

Running the engine for 3 minutes can be optional based on the guidelines. Water pressure should only be at 45 psi or lower. And the flushing position can be vertical or tilted.

Again, the propeller is initially removed. The engine should be on in neutral for at least 5 minutes. In any procedure, the water supply must not be discontinued to deliver sufficient water pressure.

Nissan and Tohatsu

Engines with 2 to 6 hp technically undergo flush plugs or bags. In larger outboards, earmuffs or flush ports are suggested. Ensure proper monitoring of water pressure and engine for almost 10 minutes.


Most Suzuki’s outboards usually use two methods. One is the flushing muff method, where the idle boat must be kept working for a few minutes at a neutral engine.

Second, the built-in port on either side or lower section of the gearcase. The engine can be turned on or off as long as the outboard is completely drained afterward.


Yamaha outboards select from flush muffs, hose, ports, or bags. Just secure cool water in performing the procedure. If the engine is in a vertical position and in neutral, run for at least 800 to 900 RPM for around 15 minutes.

Method 1: Flush Muffs

This is the most common way to flush outboard motors for engines without a flushing port.

Flush muffs are cheap but easy to access the material.  It is readily available on nearby hardware, marine shops, and even in online shops.

Once you have a flush muff, screw it to attach to the hose. Ensure to successfully slip the muffs right over the top of the water intake in the lower engine unit.

If the muffs are in place and water intakes are covered, this is the time to turn on the water. You also need to turn on the engine forcing the freshwater to circulate upwards and pass the motor system.

Keep an eye and make sure that the engine has good water flow flushing out of the outboard motor.

After running the water at the standard time based on its manual, then it’s done. Turn off the engine and shut off the water source.

Remove the muffs then you’re good to go and make your fish meal.

Method 2: Utilizing Flushing Bags

Flush bags are another recommended method for flushing outboard motors.  This durable foldable bag is placed under the outboard motor and holds an amount of water.

It’s easy to pull together by using the frame poles and connecting them. After use, the bag is then disassembled and only consumes little space for storage.

This method is effective when the boat is raised on a trailer. Position vertically the outboard motor with the flush bag below. Remove the propeller before mounting the bag.

Connect the garden hose or source of water to the bag and fill the entire bag with full water. The water level must be enough to soak the gearcase into the flushing bag.

The engine needs to be switched on once the bag is loaded with water. This will allow the cooled water to enter the inlet screen and circulate through the motor.

Run the throttle for at least 1000 RPM maximum for about 10 to 15 minutes while looking out at the withdrawn water from the pilot tubing.

Maintain a neutral engine and do not leave it unattended unless you are done flushing.

Aside from flushing, this method offers minimal noise due to submerging of the gear. Plus, it helps identify problems in your cooling system and provides repairs before usage.

On the last note, in buying flush bags, ensure to measure the size of the outboard motor so the gearcase will adequately submerge when flushing.

Method 3: Check for Built-in Flushing Equipment

Innovated designs for outboards already have a built-in flushing feature to make lives easier. Conveniently, it allows flushing even without turning on the engine, however, this does not apply to all motors.

To begin with, review the manual of your purchased outboard motor to locate the flushing area and the instructions for the flushing procedure.

Next, survey the connection where you will attach the garden hose. Let the water flow onto the motor for a few minutes depending on the stated time on the manual.

If required, turn on the engine. Be cautious in handling the connections. Avoid cross-threading in attaching the hose because this could cause further damage to the flushing port.


We hope your flushing practice went into success after finding out “how to flush outboard motor on mooring” from this article. Getting the idea of this process will certainly make your water trips enjoyable!

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