Filters in a Greener World

How to change your filter regimen in response to biodiesel, ULSD, emissions regulations and new engines

By Tom Jackson

High tech materials enable fuel filters to remove contaminants in diesel fuel that are less than 5 microns in size.

Diesel engines are getting cleaner all the time. But the issue facing manufacturers and fleet managers is that diesel is still a dirty fuel and filtering it in this clean and green age is more of a challenge than ever before.

Diesel fuel has always been prone to contamination from water, bacteria, wax and oxidation and degradation products – not to mention microscopic particles of dirt and sediment. Until about five years ago this contamination was easily handled by a dual fuel filter system – a water separator prefilter on the suction side of the pump and a much finer final filter on the pressure side.

But over the past six years engine manufacturers ratcheted up the pressure at the fuel injector nozzles – 20,000 or more psi in some cases – to make diesel engines more fuel efficient and reduce emissions. To cut emissions further, the oil companies were forced to strip out most of the naturally occurring sulfur in diesel fuel, robbing it of its natural lubricating qualities. And in just the past two years, biodiesel, with blends of up to 20 percent plant-derived fuel (B20), became the darling of environmentalists and mandated by some states and municipalities.

High pressure needs low contamination

The relatively new high pressure fuel injectors have moving metal parts that must open and close within extremely tight tolerances several hundred times a minute. The high pressure better atomizes the fuel for more compete combustion and some engines even use “multiple injection events” (typically three bursts of fuel) per piston stroke. But in this super-precise environment, any microscopic particles and contaminants that get past the fuel filters can scratch or gall the metal injector components leading to a less than perfect seal and injector tip wear.

Once they start wearing, the injectors leak fuel into the cylinder. You don’t get as much pressure, leading to reduced atomization of the fuel and poor fuel spray patterns. When this happens, the power and performance of your engine declines, you start burning more fuel than necessary and you start getting more fuel diluting the engine oil. To make matters worse, your emissions start to increase as your in-cylinder combustion sends more and more unburned fuel out the exhaust valves. Gross contamination can lead to injector tip failure and an expensive repair.

In the past, the lubricity of diesel fuel helped prolong the life of these injectors. But with low sulfur diesel (500 parts per million) mandated for off-road equipment and ultra low sulfur diesel (15 ppm) the law for on-road vehicles, lubricity became a problem. To meet those needs manufacturers put additives in the fuel, which bring back some of the lubricity, but the additives have the side effect of making it easier for water to mix with the diesel, thus requiring more aggressive water separation.

Dealing with water

Biodiesel also has an appetite for water, and the combination of plant-based fuel mixed with low or ultra low sulfur diesel, makes today’s biodiesel a very hydrophilic (water loving) fuel. Water promotes bacteria growth, which leads to acidic conditions. It can also rust iron parts and rust particles are extremely damaging to injector tips.

Biodiesel also acts as a fuel system cleaner, dissolving a lot of the varnish deposits and other impurities in your fuel lines, storage units, and machine and vehicle fuel tanks. In higher concentrations, biodiesel will raise the cloud point and pour point of the fuel. This can lead to faster filter plugging in cold weather.

On the suction side of the pump most heavy diesel engines have primary filters that prefilter the fuel and block out water. There are several ways to filter out the water. A stripping filter uses a silicon treated medium to stop water at the surface, a coalescing filter uses several layers of different media fibers to gather finely dispersed water to form drops large enough separate by stripping, and an absorption filter soaks up water while allowing fuel to flow freely.

The synthetic trend

In the past, fuel filters only needed to take out particles in the 8 to 15 micron range. But today’s high pressure injectors require filtration to less than 5 microns. To meet these demands, many fuel filter manufacturers have gone to synthetic filter media for the final filter on the pressure side of the fuel pump.

Cellulose (non synthetic) filter media are also capable of filtering down to the 2 to 5 micron range, but plug up sooner at this level of filtration. Synthetic filter media have a more open, web-like structure that holds more particles for longer periods of time and this helps to maintain service intervals. Some manufacturers combine cellulose filter media with nano-scale synthetic fibers in the base sheet or in overlays. Another strategy to maintain service intervals is to make the cellulose filters larger.

Filter manufacturers stress that while synthetic media have advantages, cellulose still has its place and each system has to be designed with a recipe that fits the application. That recipe includes an application specific system design from the prefilter/water separator through the final pressure side filter. The filter system for a heavy truck that spends most of its time on the highway will look very different from one designed for excavator that works in one place all day long.

Biodiesel and maintenance

For equipment managers who are switching to biodiesel, it’s important to take into account this fuel’s solvent-like properties. The junk it strips out of the system will quickly clog a fuel filter and you will have to change the first two or three fuel filters on an accelerated schedule after the switch to biodiesel. Once the dissolved contaminants are gone, your fuel filter PMs can return to normal.

In cold weather you may need to add a fuel line heater as a starting aid, to combat biodiesel’s high cloud point and pour point. And since water is more prevalent in biodiesel, the water separator will likely have to be drained more frequently.

To make sure biodiesel doesn’t cause you any more problems than those mentioned above, be sure to only use biodiesel that meets the ASTM D 6751 spec. Also note that while B20 has become the highest concentration of biodiesel allowed by most engine manufacturers, higher concentrations do exist. If you plan to use anything more than B20 make sure your filter seals and gaskets are rated for that fuel as high concentrations have been show to cause some gasket and seal leakage. Biodiesel may also cause problems for copper and other light metals. Make sure any filters or other fuel system components are free of these metals.

The Filter Manufacturers Council has some good technical bulletins on biodiesel and how it affects filter life. You can download these at the website: EW

Crankcase ventilation –a filter you’ll be seeing more of in the future

You may not have noticed, but crankcase ventilation systems became standard operating equipment on many new trucks starting in 2007. And given the benefit of in-cab emission reductions, CCV filters are being installed as retrofits on older trucks and school buses in many places.

How CCV Systems work -- Dirty air enters from crankcase -- Outlet returns clean air to air intake -- Pressure relief valve prevents excess pressure in crankcase --Drain returns oil to sump.

A CCV filter takes the place of the old blow-by tube. Instead of the engine venting left over cylinder vapors to the outside, a CCV filter captures them and strains out the oil particles and soot, returning clean air to the fresh air intake, or the outside depending on the design.

CCV filters take the crankcase vapors through a regulator to maintain the engine vacuum. Once the vapor passes through the regulator it encounters what’s known as a depth media, a very dense mat of fibers that trap the oil mist and soot. The soot stays trapped in the fibers and most of the oil forms droplets which drip down to the bottom of the filter where they are collected and returned to the sump.

As a general rule of thumb, CCV filters will have a 750-hour service interval, but the manufacturers we talked to recommend you check them regularly and change them whenever they become plugged. CCV filters come with a restriction indicator that gives you a visual sign the filter is plugged. A lot of stop-and-go activity, or drivers with a heavy foot will clog up a CCV filter faster.

Crankcase vapors aren’t a big source of emissions, somewhere in the neighborhood of five to 12 percent of a vehicle’s total emissions. But as the tailpipe becomes cleaner, they have a larger contribution to overall engine emissions. They also have a favorable impact on in cab emissions. And cleaning these emissions with a CCV has proven relatively easy. CCVs are likely going to be included as standard equipment on off-road engines in 2011.

Reinforcement at the core helps fuel filters withstand the rigors of operation in heavy diesel environments while stripping out contaminants and water.

The CCV retrofit market is hot right now for school buses. But there are some states and localities that are promoting their use on other vehicles and off-road equipment. Many of these areas are making money available for fleet owners wanting to retrofit. Check with your local air quality authorities for the regulations and availability of funds.

Putting emissions and environmental considerations aside, CCV filters offer the equipment owner and fleet manager additional benefits. CCV filters came out of the marine engine world, where oily residues posed a fire risk and created slippery conditions in engine rooms. By installing CCVs on your trucks and equipment, you’ll reduce the chance of oily residue building up on your engines, which will make it easier to see oil leaks and work on components. They also help you avoid polluting the ground under a machine that sits in one place for long periods of work – such as a generator.


There are loads of good resources for you on the web if you want to be better informed about fuel filtration issues and challenges. Here’s our syllabus:

Baldwin General website

Fuel Specific

Online Training

Donaldson Fuel filtration

Crankcase filtration

The Filter Manufacturers Council

Has several documents on removing water from diesel, fuel system contimination and common causes of fuel filter plugging.

Also check out this study on biodiesel and fuel filter service intervals:

and the effects of biodiesel on fuel filters:


Racor landing page

Product landing page



Home page

Wix eLearning Center; online courses and certificates:


The following people were interviewed or provided information for this article:

Baldwin Filters

Steve Englund, senior product management administrator


Brian Tucker, engine liquid product manager

Fred Schmidt, director of retrofit group, Donaldson Retrofit emissions

Mann + Hummel USA

Dennis Chamberlain, manager sales

Parker Hannifin, Racor Division

David Tice, CCV, CNG and fuel sender product manager

Steven Hardison, fuel product manager

WIX Filters

Paul Bandoly, manager of technical services/customer training