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Marine Filteration 101
A Primer on Multi-Tiered Marine Fuel Filteration

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Your engine depends on a good supply of fuel. Fuel filteration can be one of the most important parts of your fuel system. A good marine filteration system will include a tiered filering process. By having multiple levels of filteration in proper sequence you can keep your fuel clean, and keep on going maintenance costs under control.

Most recreational marine filteration system will involve a two-step process. The first part step is called primary filteration. The primary filteration happens between the fuel tank and the engine. The second step of filteration is called secondary filteration. This usually takes place at a filter mounted directly on the engine.

Important terms:
Primary Filteration
- The first fuel filteration point on most recreational marine engines. This happens between the tank and the engine.
Secondary Filteration - The second point of fuel filteration on most recreactional boats. This usually happens at a filter attached directly to the engine.

Primary filteration is usually provided by a filter provided by a third-party (not the engine or boat manufacturer). Mostly commonly the manufacturer of the filter would be Racor. Since secondary filters are usually part of the engine replacement filters should be ordered using the engine manufacturer part number.

A properly designed two-tiered setup should include primary filteration at a higher micron (30 or 10) and secondary or final filteration at 2 micron. Microns are a measurement related to the size of particles that can pass through the filter. The higher the micron rating, the larger the particles that can pass the filter. A lower micron rating will catch more but will also involve more frequent replacement. By aligning a large micron filter followed by a small micron filter you allow the primary filter to catch the big stuff and save the fine filteration of the secondary filter for getting the smaller particles.

Under most normal conditions where you have a fuel of good quality we recommend a 10 micron primary filter followed by the engine manufacturer recommended secondary filter (often around a 2 or 3 micron). If you are using fuel of questionable quality or have known fuel related issues you may want to move from a 10 to 30 micron primary filter.

The right size primary filter can substantially reduce the number of times you need to change your secondary filter.

Most primary filter assemblies can accept filter replacements of various sizes. Just because you purchased a boat with a specific primary filter size installed does not mean that you need to stick with that size for ever. If you have any questions about which fuel filters you need for your situation do not hesitate to call us at 231-759-8596 or email your questions to: