Differences Between Fuel Filters & Fuel-Water Separators

You need a fuel filter for your outboard, but which one? Many boats have two filters, so you need to know the difference between a fuel filter and a fuel-water separator.

Fuel filter vs fuel water separator

What is a Fuel Filter?

A fuel filter’s job is simple. The fuel filter is basically a screen that catches particulates (small solids) suspended in the fuel and keeps them from getting into the carburetor or fuel injection system. 

Honda replica boat fuel filter

Moeller disposable fuel filter

However, fuel filters alone don’t remove water, which would pass through the screen in the filter just like any other liquid. This is where a fuel/water separator comes in. 

What is a Fuel-Water Separator?

A fuel-water separator is exactly what it sounds like. Water is removed from fuel using a fuel/water separator. Most separators work with two chambers in the filter. 

Sierra fuel-water separator

Sierra marine fuel water separator kit

The fuel pump draws the fuel through the fuel line and the fuel-water separator. Then, the pull from the pump causes the fuel to spin in the first chamber — a centrifuge in the fuel-water filter — which causes the denser water to get thrown outside of the centrifuge and into a collection bowl underneath it. A filter with some sort of screen pulls big particulates out of the fuel, before the fuel heads downstream to the second filter and the carburetor or fuel injection system.

Boat outboard fuel filter

Choosing a Fuel/Water Separator

The most important thing to consider when choosing a fuel water separator is the flow rate of the fuel pump on your engine. If the flow rate on the fuel-water separator is lower than the fuel pump, the separator will restrict the fuel flow to the engine and hurt the motor’s performance. 

Boat engine fuel-water separator

Do You Really Need a Fuel/Water Separator?

An argument can be made that you don’t need a fuel/water separator if you have removable fuel tanks on your boat. The thinking is that much of the condensation happens when the boat isn’t running, so if you’re removing the tanks and storing them, you’re safe. However, some fuel can have water intrusion straight out of the gas station pump, so you should have something in place to separate water from fuel. 

Even with the most vigilant practices to keep water out of the fuel, water can still get into the tank through a filler cap or breather vent. If price is a concern for not wanting to get one, just know that some basic fuel-water separators are actually very affordable.

 

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