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Frequently Asked Questions:

Microns & Filters



What is a diesel filter Micron Rating?

Filter micron ratings are based on the size of particles that are removed (in lab tests) from the fuel at about 98% efficiency. So generally, a 4 micron filter will remove 98% of 4 micron-sized particles (and larger) that might make it into your fuel supply. The laboratory tests use special fuel oil and "test dust", with a specific particle size and distribution, to allow for a repeatable performance rating and comparison with other filters.

Why is the filter Micron Rating important?


Modern high pressure injection engines require at least 4 micron rated filtration at the final filter because they are highly susceptible to hard particle damage. Damage is either done gradually like sandblasting, causing poor injection performance, or instantly by plugging passages and seizing moving parts. Filters upstream serve to lower the amount of particles, water, and decomposed oxidized fuel, in the fuel stream. That's how primary filters help improve the life and performance of on-engine final (or secondary) filters. Consult your engine manufacturer for further information.


Where do small, engine damaging particles come from?

Small hard particles, basically ultra-fine wind-blown sand particles, make their way into diesel fuel supplies through poor fuel handling. Open fill ports, rusty tanks and containers, and dirty hoses and fittings, all contribute to contamination load. The size of the most damaging particles (about 4 to 7 microns) cannot be seen without a high power microscope.

What Micron Rated filter cartridge or element should I use? 2, 10, or 30 micron?

Use 20 to 30 micron when the filter is used as a pre-filter (primary), and there are secondary (final), high efficiency filters downstream. 30 micron pre-filters protect downstream filters from excessively dirty fuel.

Use 7 to 10 micron for the same reason as 30 micron. 10 micron captures more contaminants and is better at stopping water at the expense of somewhat shorter filter life. However, the fuel system will still have longer life when compared to a system without a pre-filter.

Use "2 micron" (really 4 micron @ 98% efficiency) when the filter is the only, or final filter in the system. 4 micron media is designed to protect all modern injection systems. 4 micron is sometimes used to protect difficult to service on-engine filters, moving the majority of the filtration burden to the pre-filter.

What micron filter can I use if the one I need isn't available?

You can alway use a micron level smaller than what you have been using. Filter life might be a bit shorter depending on the fuel quality, but you can't go wrong on particulate and water protection. If the filter is the only one in the system or the last one before the engine, it must be a 2 micron. Some much older engines can use 10 micron, but just in case, always go with the 2. If the filter is a pre-filter ahead of the engine mounted filter, a smaller micron size (10 instead of 30 or 2 instead of 10) will work fine until you can find the micron rating you usually use.

What is the dark, wet stuff I found coating my used diesel fuel filter?

That stuff is slime and soil bacteria that have traveled from your fuel tank. These “diesel bugs” grow and make a protective mat of slime between the water at the tank bottom and your diesel fuel. With tank agitation, or if they die due to a biocide additive, the dark slime will travel to your fuel filter, quickly plugging it. Biodiesel is more prone to this problem, but it can happen in any fuel tank; especially tanks sitting half full for a long time. That’s why diesel fuel should be filtered at every transfer. In short, your tank needs cleaning; or at least a dose of biocide and several replacement filter elements.

What is the fuel filter replacement cartridge or spin-on shelf life?

There is no maximum shelf life as long as the filter is still in the original packaging. Filters out of their packaging should be used as soon as possible. A date code is printed on top of cartridge element or on the spin-on can.


I received Racor Turbine filter (2020 or 2040) filter elements with black end-caps. Do they replace the tan end-cap filters?


In 2015 Racor changed the filter media sealing process from a heat-cured glue in a plastic cap, to more of an embedding process. The type and amount of Aquabloc media, and the superior filtration performance, remains the same. The overall element diameter is slightly reduced due to not using the tan plastic cap, and that actually helps with water removal.

My new 2010 replacement element (for a 500 Turbine Series), does not fit! it won't go down in the housing. What is the solution?

Reach inside your empty housing, grab the rubber spacer, and discard. Long explaination: Many years ago the 2010 element was re-designed with a hollow area on the bottom end cap. For old 500 Turbines, it was necessary to place a rubber ring spacer under the element to keep proper height inside the housing. New 2010 elements have a bottom ring that serves as the spacer, making the rubber spacer unnecessary.

Which way does the check ball gasket go in the 500, 900, or 1000 turbine series?

In both the 500 and 900/1000 turbine series, the flat side of the gasket goes towards the ball, and the ball is below the gasket. When re-assembling, the 500, the ball is dropped into the tan colored plastic turbine and the gasket goes on top in the flat area. For the 900/1000, the gasket is centered in the upper housing inlet hole, (a lip holds it up) before the plastic turbine is threaded into place.

Can I convert a "non-marine" Turbine Series to a Marine Turbine Series?

Depending on your vessel, you may be able to meet requirements by changing out your plastic bowl to an aluminum (non clear) metal bowl (RK 11734-03). You could also add the MA plastic bowl (RK 11-1606-1) and stainless steel heat shield (RK 11868). However, your unit will not carry a UL sticker or rating. In order to meet UL standards, marine units need to be assembled and tested at the Racor factory.

I see air bubbles coming out of the Turbine Series "turbine" inside the clear bowl. Should I worry?

This depends on the size of the air bubbles and the source of the air. Small streams of "champagne" bubbles are probably just air coming out of fuel solution. At about 4"Hg vacuum, some air may begin to appear as small bubbles. A filter mounted 3 or 4 feet above the fuel tank and/or fuel passing through elbows and tee's creates low pressure zones where air and fuel separate. Air that is the result of low pressure is usually no concern, because the air is compressed back into solution at the injection pump.

Large "blobs" of bubbles that appear to come out of the "turbine" in the bowl must originate outside of the Turbine Series housing itself. The path from the inlet port to the bowl "turbine" is direct, and surrounded by fuel; so any air must be entering somewhere from fitting to the tank. With the engine off, even the smallest fuel leak will eventually reveal itself as a wet spot. Fix these immediately.

In the end, all fuel filters eventually plug, and if not changed, air and vapor will come out of the fuel, and the engine will stop. Best to change elements at 5 to 8"Hg above start point or risk an unscheduled complete loss of power.


Do I need to replace my Racor Clear Bowl?

As a standard practice, your fuel system should be inspected regularly for problems. As part of the fuel system, Racor clear bowls must be inspected as well. Racor recommends replacing clear plastic bowls used in gasoline once a season. However, if a bowl is found to be cracked, fogged, deformed, or seeping fuel, it must be replaced immediately.

What is the difference between "UL" and "TUL" printed on Racor filters?

"UL" stands for Underwriters Laboratory. Filters used for onboard marine applications require UL certification. The "T" in "TUL" means the filter is a 10 micron rated. On other Racor replacement filters, "SUL" means "2" micron rated, and "PUL" means 30 micron rated.

How can I remove a Racor bowl that is stuck to the element can?

Heat, cold, and age can cause seals to stick and threads to bind; and the bowl may become very difficult to remove. For the best grip on the bowl, a Racor plastic bowl wrench is available (RK 22628); but a good rubber strap wrench will also work. It may be necessary to remove the assembly to a workbench, where you can apply a vise and wrench to the problem. The key to avoiding damage is to grip the filter element can only at the very ends, and never in the middle.

If the bowl turns on the element can without loosening, try denting the can slightly at the very bottom to stop the internal thread ring from turning. The element must then be discarded.

When installing a new filter assembly, it is a good idea to disassemble the element can from the head and bowl, re-lubricate, and reassemble by hand according to the instructions printed on the can.

What is the difference between an "Inboard" and an "Outboard" filter?

"Inboard" filters meet coast guard requirement for fire safety, and have metal bowls or bowl protection. "Outboard" filters use plastic bowls and drains and must be mounted in an open ventilated area. Fit, form, and function are the same.

Can I use my Racor diesel filter for gasoline?

The materials used in Racor filters for housings and seals are generally compatible with both diesel and gasoline. Racor's Aquabloc© medias filter contaminants and remove water in both diesel and gasoline. However, when choosing between Racor products, it is best to go with the filter type specifically designed for the fuel being filtered, as some gasoline applications should not use plastic filter bowls.

Other exceptions: Gasoline ethanol content should not exceed 20%; 400 Series with hand primer buttons should not be used in gasoline.

Can I use the Racor SNAPP filter for gasoline?

The Racor SNAPP fuel filter/water separator was designed and tested for use in both gasoline and diesel fuels. When "2 micron" Aquabloc© media is selected, the SNAPP can filter up to 40 gph gasoline flow.

Why would I buy a Racor SNAPP, instead of a spin-on filter?

The all engineering-plastic SNAPP has no gaskets to leak, no metal to rust, requires no tools to change the filter, and can be serviced anywhere with less waste. Spin-on filters have more possible leak points, are prone to corrosion, and require tools to change the filter; which often requires a bench to complete. Finally, the SNAPP has the maximum amount of Aquabloc© media in a compact size, along with a clear (non-removable) contaminant collection bowl.


How do I know what filter to buy to handle my fuel flow?

For gasoline, multiply your engine horsepower by 0.10; for diesel multiply by 0.18. This will give you a rough estimate of the total system fuel flow through the filter. This extra flow is used to cool engine parts on most modern engines. This amount is usually much more than fuel consumption. Choose a filter with a maximum flow rating that is more than your total fuel flow.

I need the filter wrench to remove the Greenmax, Paccar, and Freightliner clear bowls. What is the part number?

The bowl wrench for the GreenMax, Paccar, and Freightliner filters is part number RK 22628.

I have a Racor FBO filter element. How do I find the replacement part number?

The actual FBO filter element part number is not written on filter. The code on the top of the element end cap gives the specifications, which can be crossed to a part number. The first letter can be "C", "F", or "W", meaning Coalescer, Particulate, or Water Absorbing element. The next number is either "10" or "14", meaning for the FBO-10 (10 inch long) or the FBO-14 (14 inch long). The last number is "1", "5", "10", or "25", which stands for the micron rating. Consult a part number cross over chart to find the actual part number.

Where do I connect the Racor RK19669 or RK19668 Vacuum Gauge, and how do I use it?

The gauge connection must be to the vacuum side of the filter, between the filter and any pumps. You can tap into an unused outlet port or a T-fitting at the filter housing outlet. There are three needles on the gauge. The first one is the indicator, and moves with the increasing vacuum. When the filter element is new it might read about 2 inches Hg. The second needle is a follower, and is set when the element is new by turning clockwise until it rests on the indicator needle. When the engine is off, the indicator needle returns to zero, and the follower stays at the highest point it saw. The third service needle is static, and set by hand where there was loss of engine power minus an inch or so of Hg. So when the follower reaches the service needle, the element should be changed, and the follower returned to sit on top of the indicator.


My motorhome's Racor (Winn) Integrated fuel filter is (leaking, has a broken plastic cup, etc.), how can I fix it?

The Winn fuel is no longer in production and most replacement parts are no longer available. The recommended direct replacement is the Racor 790R30.

My Webb fuel filter needs maintenance. How do I service/clean the screen inside?


The screen should be inspected for any damage and replaced if necessary. You can clean the screen in a mild solvent, followed with a detergent cleaning, using a soft brush. When installing the screen, care must be take to insure no oils come in contact with the screen (don't touch with your fingers).

By Steven Hardison

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