Water-Separating Fuel Filters

What to look for when selecting a fuel filter for your boat.

November 7, 2012

Gas or diesel, an engine needs ­protection from water and particulate contaminants to keep running strong. A water-separating fuel filter shoulders most of the load. Here’s what to look for in a fuel filter, whether making sure a new boat is equipped right or upgrading your existing boat.

1. The filter element may be 2, 10 or 30 microns, indicating the size of the particles it will catch. A 2-micron filter element is reserved for secondary filtration, downstream from the primary filter. Both 10- and 30-micron filters are installed between the engine and fuel tank. Check with your engine manufacturer for recommended size to ensure the proper fuel-flow rate.

2. The inspection bowl may be clear plastic for outboard engines; aluminum for inboard and sterndrive gasoline engines; or clear with a heat shield for diesel engines. In all cases it has a drain so you can empty the filter into a jar for closer inspection. Clear “inspection” bowls have the advantage of allowing you to see water or particulate matter accumulating, and so I recommend them wherever possible. Some water-separating fuel filters have no inspection bowl — upgrading to a model that has one is advised.


3. The fuel type must match that of your boat, though some filters will work with gas or diesel.

4. The flow rate is a key specification. Make sure it matches the fuel flow, not the fuel consumed, of your engine. Some engines, like diesels, return unburned fuel to the tank, making their fuel flow greater than the fuel burn.

5. The physical size of the element is also important. All other specs being equal, a larger element will provide better service.


6. The accessories available range from vacuum gauges that indicate the element’s level of clog to alarms that light and sound at the helm when water or particulate matter is sensed in the filter, to duplex arrangements that allow you to switch the filter the engine draws fuel through on the fly, so you can keep motoring if the first filter clogs.

7. The boat should have a fuel shut-off valve upstream of the filter, preferably at the tank, if the filter is located below the level of the fuel feed outlet on the tank. This is a safety feature.


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