Frequently Asked Questions


Our thoughts on fuel polishing.

Since there are many factors of fuel contamination, water, dirt, microbial growth (fuel bugs), and tank sludge, it is hard to say that when the boat is at the dock, transferring fuel from the tank through a filter and back to the tank is fuel polishing. However, even simple filtering will remove water and contaminants, and being able to do this without running the engine is a valuable tool.

To properly clean your fuel tank, it must be opened and the interior walls, baffles and the tank bottom cleaned. Not everyone can do this, but if you can it is the ultimate way to clean your tank.

Once you have cleaned your fuel tank, the next step is to keep the water out of the tank. Water will enter your tank while fueling or through condensation. Water is heavier than fuel and will fall to the bottom of the tank. Therefore, during refueling, operate the FilterBOSS and check to see if you have taken on any water into your tank. Unfortunately, some marinas don’t really maintain their fuel storage tanks very well and you could take on a couple of gallons of water. Your diesel engine will run long enough to get you off the dock and quit somewhere in the harbor. If so, then run the system using the fuel pump and clear out any water before leaving the dock. It’s a good practice to check your fuel with the FilterBOSS.

Operating the FilterBOSS on a weekly or monthly schedule is good preventative maintenance to clean out the water and contamination that may get into your fuel. You can also operate the FilterBOSS while you are underway at sail. The sloshing of the fuel will help suspend the fuel contamination so it can be filtered out. Remember, cleaner fuel means better performance and better milage.


The purpose of the fuel filter is to make sure your engine is getting clean fuel. The most popular filter manufacturer has three filter micron sizes: 2, 10, and 30; 2-Micron being the finest. Although the 2-Micron might seem the best choice, because of the uncertainty of fuel quality, operating climates, sea conditions and maintenance schedules, the 2-Micron would clog much faster than a 30-Micron. This puts added strain on the engine lift pump, and must be monitored to maintain proper vacuum. The drawback of using a 30-Micron filter is that it allows more microns of particles to pass on to your engine fuel filter (which is most likely to have a 2-Micron filter), and each time you change your primary filter you would also have to change the engine filter. In poor sea conditions that can be quite a challenge.

We think that a good compromise is the 10-Micron filter. We use a 10-Micron on our boat with the FilterBOSS, and only change the engine fuel filter every other filter change. The vacuum gage and warning light help to monitor the vacuum on the system, and when we change the filters, we can easily service and bleed the system using the FilterBOSS’ built in fuel pump and bleed valve.

Some of our customers prefer to use only 2-Micron filters for both the primary and engine fuel filter; and then only change the primary filter. They may have a more difficult location on the engine filter that makes changing it a challenge. They will change primary filters more often, but with the FilterBOSS it only takes a few minutes and the early warning light lets you know when it’s needed.


The most popular filters are the “Spin-on” and the “Turbine” types. Both filter assemblies perform the same task: removing contamination and water from your diesel fuel, but the servicing or changing of the filter is different.

The “Spin-on” filter assembly typically requires a filter wrench to remove the filter and bowl from the assembly. After this, the bowl needs to be removed from the old filter and re-installed on the new filter. Now you must service (fill) the new filter with fuel and re-install it to the assembly. Then you should bleed the system for any remaining air.

The top loading or “Turbine” filter needs no tools. You just unscrew the tee handle, open the cover and remove the dirty filter and old seal. Then install a new filter and seal, service (fill) it with fuel, replace the cover and tighten the tee handle down. Again, you should bleed the system for any remaining air.

Both of the filter types need to be serviced with fuel after replacing. That can be a messy job in poor sea conditions. Our design of the FilterBOSS makes it easy to service the filters using the built in fuel pump and bleed port. With the fuel pump turned on, you place the spin-on filter/bowl assembly under the bleed port, open the bleed valve and fill it. From here it’s a short move to screw it back to the filter assembly. With the turbine type, just use the “Filter Filler” to service the filter. There is no need to carry the jerry can down to the engine compartment! With the FilterBOSS all this can be accomplished while the engine is running because you have switched the dirty filter to off line..

The choice we made for our boat is the Turbine type filter. It is easier to service, the large plastic bowl makes it easier to see the contamination or water and no tools are required to change the dirty filter. The replacement elements are less expensive and easy to store.

If you don’t see the answer to your question, just ask.

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