The Case for Diesel Fuel Filtration

Where’s the value in putting a $40,000 engine at risk just to save a few bucks on a fuel filter?

It’s not always clear when a fuel filter is doing its job. You put it on, you change it for another one a few months later, and since nothing bad happened to your engine in the interim you have to believe the filter worked. Few fleets cut them open to see how well they worked. Even if you did, you likely wouldn’t see anything alarming, unless you have a serious fuel system or fuel quality problem.

Contamination comes in many forms. There’s ever-present water and debris from the bottom of the fuel storage tanks. Microbial growth in fuel tanks can form algae, which can be ingested by the fuel intake line. And poorly maintained fuel systems can contain rust or other particulates.

If you’re not satisfied with the life of your fuel filters, it’s probably not the filter you need to investigate.    

“At times, variability in fuel quality (high contaminant content, additives and additive drop-out, glycerin from biodiesel production) manifests itself in the form of short filter life,” says Scott Grossbauer, global manager for clean solutions at Donaldson. “In reality, the filter is doing its intended job of removing particles of a size range at a particular efficiency and delivering contaminant holding capacity designed for the intended use.”

Today’s high-pressure fuel systems, with their extremely close internal tolerances, do not respond well to contaminated fuel.

“The average gallon of fuel can contain over 18 million potentially harmful particles, which can wear down critical components in your engine,” says Cindy Hawkins, global product manager for fuel at Cummins Filtration. “Synthetic, multilayered filtration media is a big step forward in terms of being able to remove the smallest particles of contamination with very high efficiency.”

Hawkins says efficiency in a fuel filter speaks to how good a job it does of trapping particles of a particular size — for example, 4-micron particles, which are too small for the eye to see but can harm engine components if they’re allowed to pass through the filter.

“If 100,000 particles enter the filter and 1,333 get through, then the filter’s efficiency is 98.7%,” she says. “In other words, it can remove 4-micron-size particles 98.7% of the time. That’s not bad, and typical of our previous-generation media. However, our NanoNet filters can remove 4-micron particles 99.9% of the time. That means, of the same 100,000 particles flowing into the filter, only 100 make it through the media. So, a 1.2% improvement in efficiency is actually a 13-times improvement over traditional filtration.”

Another important change has been the move toward high-performance filter media that incorporates multiple layers of media to achieve both high efficiency and long life. In the distant past, cellulose was the go-to material for fuel filtration. It evolved to incorporate micro-glass and other synthetics to achieve high efficiency in single layer media. Modern filter media offerings often still use cellulose, but it’s more for structural support. The other layers in the media enable high-efficiency filtration and provide long life by allowing effective storage of both hard and soft particulates.

“Fuel filters are subject to the additional challenges of a dynamic environment, including vibration, flow changes and pressure pulses,” Grossbauer points out. “All filters are not created equal, so it’s important to understand what is hidden underneath the surface of the filter.”

The trouble with water

Fuel’s main enemy is water. It’s always there, and while sometimes it’s visible, it’s the water you can’t see that you have to worry about. Unlike diesel fuel, water cannot be compressed, and that creates problems for fuel pumps and injectors.

“Water is more hazardous to the injectors than contaminants,” says Donald Chilton, Wix Filters’ director of product management. “While many filters look similar, the media is very important. Many of today’s products are designed to strip the water out before it can get to the injector.”

Fuel filters and fuel/water separators coalesce the very tiny particles of water and trap them in the filter. Fuel/water separators often have glass bowls where the water can be seen and drained away. Other filters trap the water internally. You may not be able to drain it, but at least it’s not getting into the sensitive mechanical systems.

Water can be picked up anywhere, from the supplier’s tanks to the humidity inside truck fuel tanks. While it can be messy, some maintenance managers make a habit of draining water from their fuel tanks periodically to keep it out of the filters. Wix Filters and others offer diesel fuel test kits to help monitor the health of fuel, allowing fleets to adjust fuel water absorbers, breathers and/or additives as needed.

“These are a good way to catch problems before they start,” says Chilton.

Choosing a filter

Advances in filter technology are keeping pace with engine makers’ filtration requirements, but still, a dizzying array of choices remain for fleets. Which filter do I need? When do I change them? How do I know they are working while providing a good value for the cost?

Here are three things to consider when making filtration choices:

1. “If your fuel filters aren’t making it from PM to PM, the real problem may be fuel quality, not the filter,” suggests Hawkins. “Short filter life is usually a symptom. Talk to your fuel supplier about what they do to reduce condensation and other contaminants during transport and delivery, and what you can do at your fuel islands and storage tanks not to invite contamination in the first place.”

2. “Follow the OEM’s recommendations for filter specification and change intervals,” advises Grossbauer. “If you have a premature plugging problem, investigate to find out what’s causing it. And when filters do plug, don’t change them out for filters that are less efficient just so they will last longer.”

3. “Never assume a 2-micron or 3-micron filter is necessary,” Chilton says. “Those filters may be too tight for your application and will end up starving your engine. Always use what is specified by the manufacturer. And make sure drivers or technicians are draining the water as needed. If there are multiple filters, always change both the primary and secondary filter at the same time.”

And one last word of advice: Avoid fueling when a station is getting a fuel delivery. The downflow of fuel into the underground tanks stirs up the sediment that normally rests on the bottom of the tank. You might be pumping all that junk right into your fuel tanks.