Should You Flush Your Outboard? Essential Boat Maintenance Tips

We all understand the importance of regular boat maintenance, but should you flush your outboard?

The majority of outboard manufacturers suggest performing a freshwater flush anytime the boat is driven in saltwater. This practice clears the cooling passages, removes residue, and eliminates scale that would accumulate.

Over time, this buildup impedes the cool water flow through the engine, thereby reducing performance.

However, you don’t want to overlook the importance of flushing your outboard after being used in muddy or silty freshwater either.

Thankfully, flushing your outboard is a simple procedure that doesn’t take long. You just need to follow some basic steps.

Why Flush Your Outboard?

Brackish water and saltwater are both considered corrosive agents to the outboard’s aluminum. If you don’t remove this corrosive agent, it build ups inside the cooling passages.

flush your outboard

Over time, this buildup leads to a blockage in the cooling system, which could cause your engine to overheat. Plus, the agents are going to corrode your marine engine, and you won’t see it happening.

That’s because this corrosion occurs from the inside out.

Every single outboard manufacturer instructs owners to flush your outboard. Whether you are driving in salt, dirty, brackish or polluted waters, you want to perform the procedures after each operation.

However, don’t overlook the need to flush your outboard after operating the vessel in muddy or silty fresh water. While you might not need to do it every time, you should still consider periodic outboard flushing.

How Long Should I Flush My Outboard Motor?

The majority of manufacturers agree that flushing for ten minutes is ideal. You will want to perform the flushing procedure while the outboard is running at idle speed, and the engine is in a vertical position.

However, you won’t need to run the engine if you use the flushing port.

Once you have finished flushing, keep the motor vertical until all of the water drains out of the powerhead.

If you have an inboard motor, the procedure is very different, as it can’t be easily flushed.

How Do You Clean an Outboard Motor?

The majority of instructions for cleaning outboard motors remain the same, no matter what manufacturer you use. However, it’s always best to reference the owner’s manual and follow any recommendations given.

If you don’t have the owner’s manual, spend a few minutes online researching what the manufacturer recommends.

Flush Your Outboard Motor with Built-In Flush Connection

Outboard motor flush

The majority of recent outboards have a built-in flush connection. If your motor is older than 15 years old, you might not have one and would need to choose another method.

This built-in connection utilizes a threaded fitting or a snap fitting adapter to connect a garden hose to the motor.

Look for this fitting on the engine, facing toward the boat. It could also be found under the cover in the boat motor’s midsection or under the cowl.

If your outboard has this fitting, you don’t need to start the engine. In fact, it’s designed to flush the outboard without ever starting the engine. We recommend reading the owner’s manual for more instructions.

In our opinion, it’s best to use this connection while at the dock. Just flush the motor once you’ve tilted it clear from the water.

  1. Turn the engine off.
  2. Tilt the outboard clear of the water.
  3. Connect the hose to the motor.
  4. Allow freshwater to run for an estimated ten minutes, or based on manufacturer recommendations.
  5. Allow the outboard to remain vertical until the water drains.

It’s important to note though if the engine is on a trailer, and you tilt it all the way up. If the trailer is on a hill or the tongue is jacked all the way down and allows the engine to tilt so far up that the lower unit is above the power head.

You can fill the engine with water when flushing it. This is an EXTREMELY RARE case, but it can happen, so be mindful that when tilted up and on a trailer that the powerhead of the engine is not tilted up so far that allows the lower unit to be above the powerhead.

Some boats also come with a flushing attachment built into the boat as well, this is something that you can do! Here’s a video explaining how:

Flush Your Outboard Motor with Earmuffs

If your outboard doesn’t have a built-in connection, you can use flush muffs. These look similar to large earmuffs.

The V-shaped device slips over the outboard water intakes, which are located behind the propeller. With a metal clamp or spring, the muffs are held in place.

Then, you attach a garden hose to the rubber cup. You can follow these directions with most outboard engines.

flush outboard motor
  1. Once the cups are attached to the gearcase, start the water flow.
  2. Allow the engine to run in Neutral. The propeller won’t turn in this position, which is good. Otherwise, the propeller would turn, which isn’t good.
  3. Once the motor is started, you should see the water flowing. This ensures that the water is pumping through the motor.
  4. Allow the engine to idle in Neutral. This should occur for about ten minutes.
  5. Don’t allow your boat to be unattended during the process. If the muffs don’t have a tight enough seal or fall off, you must shut down the motor immediately. Otherwise, the water pump impeller could become damaged.
  6. Turn off the engine before you shut down the water supply.
  7. Allow the water to flow out completely.

Keep in mind that not every outboard can be flushed with muffs. A few manufacturers use multiple water inlets that simply cannot be covered.

Others require using duct tape to seal off the additional water inlet locations.

If you aren’t sure, read the owner’s manual or reach out to the manufacturer. Some might recommend that you remove the propeller before using flushing muffs.

Flush Your Outboard Motor with Buckets or Bags

A flushing bag is made from soft plastic, vinyl or canvas that works with a garden hose fitting. It’s simple to use and doesn’t require expert skills. You can also even take a large 55 gallon plastic trash can and cut it down to work with your engine.

However, when using flushing bags, you might need to remove the propeller from the outboard. Then, follow these steps.

  1. Put the boat on a trailer, with the engine tilted down.
  2. Fit the bag around the gearcase.
  3. Fill the bag or bucket with water.
  4. Make sure you cover the cooling water inlets.
  5. Start the motor to pump water out of the reservoir. The hose is responsible for maintaining water levels.
  6. Don’t leave the engine unattended as you watch the water flow freely.
  7. Make sure all of the water drains out once the flush is complete.

You can also flush your outboard with these steps by using a large barrel or pail. Just make sure your water supply maintains a water level in the container that is above the inlets of the gearcase.

Outboard Maintenance isn’t Difficult

You can’t overlook the value of overall boat maintenance, including flushing your outboard. For the minimal price you will spend on maintenance, you save yourself a lot of trouble in the long run.

However, flushing the outboard is just one step to a bunch of tasks you must perform.

Consider the value of cleaning your outboard engine, which we outline in the following video.

Additional service items that shouldn’t be overlooked include:

  • Engine fuel filter
  • Boat fuel filter
  • Air filters
  • Oil filters
  • Water pump impellers
  • Thermostats
  • Belts
  • Spark plugs
  • Belts
  • Lower unit seals
  • Sacrificial anodes or zincs

With some due diligence, you ensure that your outboard and boat run as intended for many years – allowing for plenty of enjoyment.

Check Us Out!

Take some time to browse our YouTube channel for more step-by-step guides and practical tips.

We also recommend checking out these helpful articles if you want to learn more about your boat and the engine.

Brian Jones

Brian Jones has spent most of his career as an ASE Certified Master Tech. Today, he spends his time freelance writing and consulting. He lives outside of Dallas, TX with his family and loves anything mechanical.

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