How to Change Fuel Water Separator on an Outboard

The presence of water and contaminant in fuels have been proven to be why clogging occurs in engines. A fuel-water separator filter is among a series of filters that make certain impurities do not get to the sensitive areas of a boat engine.

Regular replacement of the filters enhances engine efficiency. Therefore, high performance, and low maintenance costs.

Therefore, it is essential to regularly change the fuel-water separator filter and replace it appropriately.

This article explains a step-by-step process of changing a fuel-water separator filter on an outboard.

What is a Fuel Water Separator?

Water separating fuel filters are mechanical devices installed in a boat’s motor to act as an added layer of defense for its fuel system.

As their name suggests, the fuel water separator filters filter water and particulates before reaching the engine to prevent mechanical failure. This, in turn, allows for the flow of clean fuel into the machine.

Unlike regular fuel filters, water separator filters target water by distinguishing the densities of water and oil. It is essential for vessels like boats that operate in water environments.

The water separator filters allow the flow of water and oil to a certain point.

Then, it distinguishes the two liquids from their weight, allowing water and other particulates to settle to the bottom of a bowl while the pure fuel continues to flow into the engine.

Typically, a fuel water separator filter is installed at the bottom of the fuel end line. This allows it to use the fuel’s suction instead of going through the engine.

Read More: Best Oil Extractor for Boat

6 Steps to Change Fuel Water Separator on an Outboard:

To change a fuel water separator on an outboard, you need to have the following tools with you:

  • Flathead screwdriver
  • Spanner
  • Drill with drill bits that are sized right for the mounting holes
  • Fire extinguisher
  • Rags for post-installation cleanup
  • Fuel container
  • Universal wrench
  • Blanking plugs for isolating the separator
  •  Fuel hoses
  • Clamps for the fuel hoses

Step 1: Preparation

First, locate the old separator filter in the boat. In most vessels, it is situated in the back of the transom section, in the starboards, or under the bilge.

Next, cut off the electricity and fuel hoses to avoid electrocution and fuel leakage.

Step 2: Detaching the Old Filter

Before you begin, place an absorbent rag underneath the old filter. It is essential to collect the fuel that will spill off while detaching.

Next, position the wrench around the filter, fasten it and turn it anticlockwise. Once it is loosened, you can separate the rest of the way using your hand. It also minimizes spillage.

Step 3: Examining the Fuel

Once detached, empty the Filter contents into a transparent container and examine it for water, particles, and other impurities. Please leave it to settle down as you unpack the new filter.

Step 4: Preparing the New Filter

Unpack the new fuel-water separator filter and examine it to check that all its components are in place.

Before installing it, make sure to put some clean fuel into it. It should be done to near full. It eliminates the possibility of air being trapped inside it, interfering with smooth fuel flow into the engine.

Filling of the Filter can be done in two ways:

  • Get clean fuel from a container and pour it into the filter. As already mentioned, it should get near the brim.
  • Using the primer in the fuel lines.

Step 5: Attaching the New Filter

Place the new filter in place and tighten it by subjecting it to clockwise moves. When you feel it can no longer move, grab a rag around it and place the wrench on top of it.

Give it a quarter of a turn. Appropriate tightening ensures no air is sucked in and makes replacing it next time.

Note: If the filter was not filled before attaching it, this is the time to do it using the second method above.

Now disconnect the motor side of the fuel hose. To do this, unfasten the jubilee clips around the hose using the flathead screwdriver and pull it off. Then, press the primer bulb as you place it and remove your thumb on top of it rhythmically.

This is done to generate a suction force that will pull the fuel from the tank and into the filter. You should be able to hear the fuel dropping into the filter as you press the primer.

Reconnect the hose and tighten the jubilee clips.

Step 6: Final Checks and Testing the Engine

Use the rag to wipe off any fuel spilled underneath the filter and on the filter itself. Examine to make sure everything has been fixed correctly, and no leakages are visible. Turn on the engine and watch for any further leakage.

Please take out the boat and test it on a short stretch at high speed. If no issues are noticed, the fuel-water separator has been changed successfully.

The old filter’s fuel can be discarded or reused depending on its quality.

Symptoms of a Bad Fuel Water Separator for Boat

Here are common symptoms associated with a badly clogged or damaged fuel water separator for a boat;

Engine Sputtering

A faulty fuel water separator causes the boat engine to sputter during motion. This can be a result of the engine not receiving enough fuel.

If you notice any engine sputtering in your boat, it might be due to problems associated with the water separator.

The dysfunctionality of the Engine

The engine sputters when the boat carries heavy loads. This, in turn, overworks the water separator causing it to clog and limit fuel supply to the engine.

Ultimately, the engine loses its efficiency, and its performance declines.

An Abrupt Rise in Temperature of the Engine

You might suddenly notice an abnormal increase in the temperature of your engine.

Understandably, an increase in your engine’s temperature could be caused by a variety of difficulties.

Some of which can be due to a faulty water separator, the engine being overworked, or overheating, to mention a few. You must take your boat to a repair shop for proper check-ups and repair.

Other symptoms include frequent idling and sputtering, solid odors, decreased speed and fuel efficiency, hard starting, and engine stalling.

In some cases, you may also notice random misfire and excess exhaust emissions, or even a damaged fuel pump.


Ultimately, any motor vessel depends entirely on fuel to run. Thus, impurities or contaminants like water in the fuel impede an engine’s life span and performance.

Therefore, to keep your energy clean and pure, you have to periodically replace the filters, even when they appear in good form.