Guide to Fuel Filters

Fuel Filter : What is it?

Fuel Filters

A fuel filter cleans and maintains the engine fuel system of a boat, so it can operate successfully in a water environment.  Unclean fuel can cause the engine to stop, slow down, or damage the engine.  The fuel filter screens out rust and dirt particles from the fuel and protect it from getting contaminated with paint chips and dirt knocked into the tank while refueling.  Rust and other particles are caused by moisture in the steel tank, and if these particles are not removed immediately, their abrasive action can damage the pump and injectors. The fewer contaminants are in the fuel, the more efficiently it can be burnt. The fuel filter should be maintained regularly by cleaning it at regular service intervals. After a while, it should be replaced with a new one because an unclean fuel filter becomes clogged with contaminants and restricts fuel flow. This causes the engine's performance to drop as it struggles to draw enough fuel to continue running normally.     

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Types of Fuel Filters

Fuel FiltersFuel Filters

Kinds of Fuel Filters include the following:

Pretank filter

A pretank filter is a funnel type of filter that provides basic filtering when fuel is pumped or poured into the tank. It can be a plastic funnel screen that catches dirt, leaves, and large contaminants such as plastic bits, or an aluminum funnel designed for cruisers that travel remote cruising grounds where fuel is scarce and supplied in used drums of dubious origins.   

An aluminum funnel has two fine stainless steel mesh screens for trapping fine particulate matter such as dust and sand. It has a water-resistant filter for keeping out majority of the water that can be present in the fuel. It is designed for diesel fuel, but it can also be used for gasoline. It protects the tank from water contaminated with bacteria and helps prolong the life of the primary and secondary filters.

Primary filter

A primary filter is an off-engine after-market filter added to the fuel system.   It comes in single or multiple units, spin-on element or turbine, and in-line or independent mount.

The newest type of primary filter is the spin-on element, which is similar to filter used in cars. It is commonly used in gasoline engines, and it is easier to replace than a turbine unit. It can come as a stand alone filter or as a combination filter and water separator. A turbine filter is commonly used in diesel engines.  

Secondary filter

A secondary filter is a screen in the intake line of a gasoline carburetor. It can also be a canister-type filter mounted directly on a diesel engine. If the primary filter system is efficient, maintaining a secondary filter should not be a problem except for annual service maintenance.


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Choosing Fuel Filters (Buying tips)

Size:  Choose a fuel filter sized for the flow rate, and not for the consumption rate, of the engine.  A gasoline engine burns or discharges all unburnt fuel fed into it, while a diesel engine returns used fuel to the tank. So, a diesel engine has a larger flow rate but consumes less fuel than gasoline per hour. The fuel filter you should get should have a size in accordance with the projected fuel flow per hour required by the specific size of the engine. The rule of thumb for sizing the filter of a gasoline engine is 10% of the maximum horsepower equals gallon per hour.  Choose a fuel filter that is a bit oversize for the projected gallon per hour because it lasts longer than the one in the exact filter size.  Also, a fuel filter that is too small restricts fuel flow and causes performance problems.     

Vacuum gauge:  Choose a fuel filter with a vacuum gauge for determining the cleanliness of the filter.  It should show how hard the engine is trying to pull fuel through the filter. The higher the vacuum, the dirtier the fuel filter is, and the more you need to replace the element and clean the filter unit.


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