Fuel Filters are Key to Fuel Tank Cleaning
& Continuing Tank Maintenance

Fuel Filter Questions

Questions about fuel filters are common as there is a lot of very technical aspects of fuel filters that are not always clearly set forth on “the box”.  In addition, what purpose the filter is meant to serve is not usually provided, resulting in most folks thinking that a fuel filter is just a fuel filter and they are all basically the same.  Generally, the price of fuel filters vary greatly for what appears to be the same filter, but, as in most cases, you typically do get only what you pay for.

The filters that are available on the diesel-fuels.com web site are specified to serve the purpose of a fuel tank cleaning and fuel maintenance re-circulation system.  These filters do not have the more advanced filtration media that may be required to substitute for an engine manufacturers filter that is designed to provide the last line of defense against contaminants that would otherwise ruin an expensive set of fuel injectors in a modern High Pressure Common Rail (HPCR) fuel injector system such as are now common on most diesel engines.  For more information on what these engines are subjected to in day-to-day operations, read the Article entitled “Diesel Fuel and Injector Failure” on this web site.

Tank Cleaning and Fuel Maintenance

We have Tank Cleaning and Fuel Maintenance Systems that fall into four categories.  The following is a short summary of each:

  • TK Series Portable Systems – hand held tank cleaning systems for tanks up to 1,250 gallons that require periodic cleaning as needed
  • FPS Series Compact Systems – Fuel Polishing Systems that are dedicated to maintain a fuel tank(s) in one location and assure fuel is in peak condition.  Ideal for tanks up to 15,000 gallons and tanks that may take on lower quality fuel (such as marine applications).
  • MTC Series Mobil Systems – Mobile Tank Cleaning and Fuel Polishing Systems are the “workhorse” systems often going from tank to tank regularly cleaning badly contaminated tanks and then re-visiting periodically to maintain fuel tank cleanliness and optimal fuel quality.
  • STS Series Fuel Maintenance Systems – Fuel Tank Maintenance Systems that are highly automated for maintaining stored fuel in dedicated tanks up to 60,000 gallons, having advanced Programmable Logic Controllers, and exterior enclosures assuring fuel tank cleanliness is maintained and fuel quality is optimal when needed.

Note that none of these systems are intended to replace the fuel filter on the diesel engine.

Cleanliness of Diesel Fuel at the Engine

The process of cleaning a fuel storage tank involves considerations not typically considered in specifying fuel filters that provide that last line of defense to an engine.  Fuel contaminated with particulates larger than 4 microns can do great damage to an HPCR fuel injector system and reduce the life of an expensive set of fuel injectors to just a few thousand miles.  By assuring that the fuel that is fed to an engine has a reasonable low level of contamination, the engine manufacturers filter is capable of performing its duties of bringing the contaminant level down to that required for the particular engine without expecting a high level of contaminant capture by the final filter, thereby shortening the useful life of the final filter and unnecessarily increasing filter expenses.

Diesel Engine Manufacturer’s Warranty Requirements

All major diesel engine manufacturers have set minimum fuel standards for the diesel fuel to be used in their engines, and failing to maintain the fuel that you use in a manner so that it meets those standards could lead to engine component failures and denied warranty claims. As an example, Caterpillar has published “Cat Commercial Diesel Engine Fluids Recommendations” (SEBU6251-17 September 2014 [a more recent version may be available]) that states “In order to meet expected fuel system component life, 4 micron(c) absolute or less secondary fuel filtration is required for all Cat diesel engines that are equipped with common-rail fuel systems.” (Page 34) You should not assume that fuel being delivered to you meets the manufacturers requirements, and certainly fuel that has been in your storage tank for an extended period of time may not meet requirements of diesel engine manufacturers. Additional cleanliness standards apply to diesel fuel. Caterpillar recommends that the fuel dispensed into the machine tank meets “ISO 18/16/13 cleanliness level.” (Page 49) For more information on fuel cleanliness specifications and requirements, see the “Diesel Fuel and Injector Failures” discussion on this web site.

Diesel Fuel Shelf Life

Even when all fuel storage maintenance practices are followed, Caterpillar recommends a maximum of 1 year from production for distillate ULSD diesel fuel storage, and a maximum of 6 months from production for bio-diesel and blended bio-diesel storage. Storage life for bio-diesel and bio-diesel blends that are greater than B20 may be much shorter than 6 months. (Caterpillar® Commercial Diesel Engine Fluids Recommendations – Fuel Specifications – page 45 – SEBU6251-17 September 2014)  Google this document number for a complete copy.

Under normal storage conditions, today’s diesel fuel when stored at temperatures no higher that 68 deg. F (20 deg. C) can be expected to stay in usable condition for 12 months. Stored at temperatures higher than 68 deg. F (30 deg. C), Fuel can degrade to unusable condition in as little as 6 months. Increased use of above-ground storage tanks have made these problems even more wide-spread.

How Clean is Clean?

The ISO 4406 cleanliness code is used to quantify particulate contamination levels per milliliter of fluid at three sizes: 4 µ, 6 µ, and 14 µ.  The ISO code is expressed by three numbers (i.e. 19/17/14).  Each number represents a contaminant level code for the correlating particle size quantity.  The code includes all particles of the specified size and larger.  It is important to note that each time a code increases, the quantity range of particulate is doubled.

Diesel Fuel Cleanliness

Note in the above illustration, the fuel is given as having a 24/22/19 cleanliness rating as it enters the filter.  With the first number being 4 micron, the fuel as tested contained more than 80,000 particles per milliliter.  The fuel coming out of the filter is given as having a 16/14/11 cleanliness rating.  On the table, this translates to showing the fuel as tested contained less than 640 particles per milliliter, a level 0.8% of the pre-filter sample (99.2% of 4µ particulates were removed).  Note in the discussion above of the recommendation of Caterpillar of the cleanliness of fuel dispensed into the machine of 18/16/13.  By maintaining your stored fuel at this level, you are assured that the fuel is what Caterpillar requires and will preserve your equipment and protect your warranty.  The will still pass through the engine manufacturer’s primary and secondary filters.  This level allows for 4µ  particulates up to 2,500 particles per milliliter.

Cleaning Diesel Fuel Storage Tanks

How Big is a Micron?The fuel being cleaned may be old and is showing signs of having a build-up of sludge, floating slimy debris (sometimes erroneously referred to as “algae”), water accumulation in the tank bottom, and fuel that has degraded to the point where it has a distinctly brown or black appearance.

The normal procedure when initially cleaning a fuel tank is to start the re-circulation process with a coarse filtration media to “take out the big pieces”.  The MTC systems are equipped with either an FP Series Purifier & Centrifugal Fue / Water, Sludge & Particle Separator that will remove heavy contamination and free water without the use of a replaceable filter, or a PF Series Bag Filter Vessel that has a stainless steel “basket”.  Although the basket usually holds the bag filters, it may also be used without bags to remove the sludge.  After the sludge and heavy debris is removed, bags, that are rated from 800 microns down to 5 microns may be used to remove progressively smaller particulates.  These bags are relatively inexpensive and may be cleaned out and reused until they develop a hole or tear in the bag.

After free water and the sludge is removed and the fuel is relatively free of the floating/suspended clumps, the finer filtration media in spin-on fuel filters is utilized by simply throwing a valve or disconnecting the discharge hose and relocating it to a secondary discharge connection.

Fuel filters are usually marked with a micron rating, such as 4 micron, 10 micron, 25 micron, etc.  However, the micron rating does not tell the entire story that you need to know as filtration efficiency is an important factor.

Fuel Filter Efficiency

Generally, an efficiency rating is provided by the filters manufacturer.  It may be stated as a “nominal” rating, or an “absolute” rating.  As an example, the FF-10 filter that is used on many of our STS Fuel Maintenance Systems and as the secondary filter on the MTC Series Systems is rated at 10-microns.  But to understand the filter’s efficiency, it is 50% efficient at removing particulates larger than 5-microns, giving it a nominal beta rating of 2 (β5µ(c)=2). This filter also is 98.7% efficient at removing particulates larger than 19-microns, giving it an absolute beta rating of 75 (β19µ(c)=75).

The efficiency rating of each filter is provided in the description of that filter in the product shopping cart.

Absolute Filtration and Water Block Filters

There is also available several filters that serve a specific purpose.  The FFZ-3 filter is made up of a special “X-Glass” filtration media that provides absolute 3-micron filtration, and two “Water Block” filters in 3-micron and 10-micron each with specially treated filter media that sheds water from the fuel stream and captures up to 15 oz. of water from fuel within the spin-on canister.

Filtering Fuel is not Fuel Polishing

Filtering fuel does not have an impact on microbial contamination or the presence of bacteria or fungi.  This growth cannot be filtered out of your diesel fuel.  Also, filtering diesel fuel does not turn dark brown or black fuel clear and bright.  This process requires a Fuel Conditioner. To understand how a Fuel Conditioner impacts microbial, bacterial and fungal growth in your fuel, please review the article “Why Bacteria Hate Magnets” on this web site.

Don’t be fooled by those who sell a fuel filtering process and the addition of chemical biocides to your fuel as “fuel polishing”.  For a thorough understand of what is involved in the process of Fuel Polishing, please review the article “Diesel Fuel Polishing” on this web site.