The presence of water or other fluid mixed with diesel fuel is clearly apparent from the stratification shown here.

The presence of water or other fluid mixed with diesel fuel is clearly apparent from the stratification shown here. 

Diesel fuel is generally very clean when it leaves the refinery. But it can pick up contaminants as it travels through pipelines, terminals, delivery trucks, underground storage tanks and dispensing equipment on its way to a truck’s saddle tank. If you don’t take steps to keep it clean, it can degrade your fuel economy, damage expensive fuel system components and cause downtime. That’s never been more important than today.

“EPA clean air regulations have driven engine technology to places it hasn’t been before,” says Scott Grossbauer, director of Clean Fuel Solutions, a division of Donaldson. The high-pressure common rail system used on today’s low-emission diesel engines provides higher pressure and better burn. The downside is that these fuel systems have tighter tolerances – meaning there’s much less space between system components.

Just how small are we talking about here? “Prior to the last emissions change [in 2010] we were trying to remove particles 10 microns and larger,” explains Russ Bretell, manager of education for Cummins Filtration. “Today with the tighter tolerances, we’re trying to remove particles that are 3 to 4 microns and larger. That’s 3 millionths of 1 meter, which are particles smaller than blood cells and getting down to the size of bacteria.”

That means fuel has to be cleaner than ever before. “Unfortunately, while in North America we have about the cleanest fuel in the world, it’s still in many cases doesn’t meet the ISO [International Standards Organization] code for cleanliness,” Bretell says. If these contaminants get into a truck’s fuel system, they can cause wear and damage to the fuel injectors, leading to poor combustion, bad fuel economy and further engine damage.

The first symptom of poor fuel quality will be plugged filters on bulk storage tanks or trucks. Instead of assuming it’s a filter problem, look to the cause. “Our mantra is, a plugged filter did its job,” says Donaldson’s Grossbauer. If it’s not, “you may find yourself with injectors and pumps failing prematurely. That’s when you have to look back and find out what issues” you’re having with fuel contamination.

The Enemies of Clean Diesel Fuel

Water is the most common fuel contaminant and perhaps your engine’s biggest enemy. It can reduce fuel’s lubricating qualities and cause injector seizure and engine damage. “Free water is probably the single biggest cause of fuel system failure,” Grossbauer says. “Most engine manufacturers require that zero free water reaches the high-pressure, common-rail fuel system, which often means that water in the fuel can lead to denied warranty claims.”

Water boils and vaporizes at a low temperature compared to that of fuel combustion. “If there’s water in the injector tip and it’s introduced to thousands of degrees of heat, then that water can expand and actually damage the injector,” Bretell says.

Eliminating water in fuel will not only protect your fuel system, but also will reduce rust, corrosion, wear, fuel degradation and other damage. Water is common in bulk fuel storage tanks because of condensation.

“We’ve had customers pull a transfer pump out of a tank for repair, and it’s very rusty and they’re very surprised,” says Steve Muth, Penray’s chief chemist. “Fuel doesn’t rust. So that’s when they realize they have a problem.” Rust is only part of it, though. The water in fuel tanks also is a perfect place for microbes, fungus and bacteria to grow. Those biological contaminants can clog the filters of storage tanks and then trucks.

“As your filters clog up, you’re reducing efficiency of the filter and your fuel is not burning as cleanly, so you’re not getting the maximum mileage and power out of the fuel,” says Penray spokesman Mark Kardon. Says Grossbauer at Donaldson, “We usually attribute poor engine performance to worn engine hardware, related to the injection system. Unless the fuel filter is plugged to the point where an adequate amount of fuel can’t get to the engine, then performance will be off as well, but usually to the point where the truck can’t be driven.”

In addition, over time, the water and microorganisms in the fuel can corrode fuel storage tanks. “We find corrosion to be sort of a hidden problem,” Muth says. “We believe it’s more significant than people know. They will see black bacterial deposits or problems with their filter, but they don’t realize how much corrosion is in the tank.”

Some tank owners can make the problem worse with certain additives, Muth says. “There are products out there that talk about making the water disappear, making it ‘burn,’” he explains. “What they do is they dissolve the water into the fuel to force it to be carried through your engine. With these new high-pressure, high-performance injectors, that’s a bad idea.”

Water in the fuel can also lead to premature wear of fuel pumps and other system components that rely on the lubricating properties of diesel.

Water formation isn’t limited to bulk storage, points out Cummins’ Bretell. He explains that some engine designs use fuel to cool the injection pump. When it circulates back into the tank, it carries that heat with it and raises the temperature of the fuel in the tank. As the fuel is consumed, air comes in, carrying moisture with it. If that moisture-laden air is cooler than the fuel, you get condensation. So most vehicle engines have a fuel/water separator or a primary filter that also strips water from fuel. 

The presence of bacteria and fungi in conjunction with water in fuel causes corrosion to develop in storage tanks. Along with water, rust, dirt and bacteria settle to the bottom of the tank and ultimately can penetrate tank walls.

The presence of bacteria and fungi in conjunction with water in fuel causes corrosion to develop in storage tanks. Along with water, rust, dirt and bacteria settle to the bottom of the tank and ultimately can penetrate tank walls.

The increasing use of biodiesel has made problems with water and bioorganisms worse, according to Penray.

“Biodiesel can carry a lot more water,” Muth says. “It’s a great fuel for these bugs.”

According to Gary Bilski, chief engineer at Luber-Finer, the Society of Automotive Engineers’ committee on liquid filtration is working with the ISO to take biodiesel into account in revising standard tests used to evaluate filters.

Filter manufacturers have already been redesigning fuel/water separators to better work with biodiesel, Bilski says. For instance, Luber-Finer recently came out with a new filter with a triple layer of media that has 95% water removal properties when used with biodiesel.

At Wix Filters, in addition to mixing media, engineers are developing better ways to deal with water, says Marty Rhodes, technical service and customer training manager. Coalescing filters, for instance, would encourage the microscopic water droplets trapped in the fuel to join and stick together, or coalesce, into larger droplets that could be more easily removed. Another new approach is hydrophobic media, which repels water.

Water and the bio-organisms that feed on it, of course, are not the only contaminants in diesel fuel. Particles of dirt, sediment and other solids can make fuel injectors wear out prematurely and fail, according to Pete Cochefski, director of Ryder Fuel Services. Today’s high-pressure rail injectors are especially vulnerable to clogging from dirt and contaminants, he says.

Donaldson’s Grossbauer says other problems can result from fuel additive instability. Some additives can fall out of solution, especially when combined with other contaminants, such as water. “It’s kind of a host of chemical mysteries that we’re trying to solve.”

Bulk Fuel Storage Tanks

Averitt Express rarely sees issues related to contaminated fuel, says Shane Nelson, maintenance coordinator. “In nearly every case it was due to an associate fueling off site from an Averitt facility or due to driver error in dispensing DEF in fuel or fuel in DEF.”

The Tennessee-based fleet and logistics operation has its own bulk storage and dispensing locations at the majority of its facilities serving its approximately 4,000 trucks. “We utilize a dispensing filtration system set up on a scheduled maintenance program, additives, inspections, along with an associate corporate group dedicated to monitoring the fuel program,” Nelson says.

Not all fleets are as conscientious. A few years ago, Donaldson started a push on education about bulk filtration. “Some people don’t have any filtration on bulk tanks at all,” Grossbauer says. “Some people have it, but it’s not efficient enough to really capture contamination that will do harm on the vehicle.” Relying only on the vehicle filtration will lead to shorter filter service intervals and potential fuel system damage.

There are filtration upgrades available that can do a better job of keeping the fuel clean in storage tanks. “One of the easiest things is to install a breather filter,” he says. Breather pipes allow air to enter and exit fuel storage tanks, he says. “A lot of times it’s an open pipe or a mesh screen that doesn’t stop contaminants from coming in.”

You also need to think about contaminants during the filling and dispensing processes. Ideally you would filter fuel on its way in to the tank from the supplier, so any contaminants are stopped before they get into your storage tank. This would be too expensive to add to most existing in-ground storage tanks, says Ryder’s Cochefski, “but on above ground tanks it’s a lot easier to be able to install filtration on the fill.”

At the least, make sure you’ve installed proper filtration at your dispensing pumps, a last chance keep contaminants from getting into the engine.

“What we’ve been doing for some customers is installing external filtration on the dispensers before the hose and nozzle,” Cochefski says. There are two types, one that removes particulates and the other that removes water from the fuel.

In addition to proper filtration, storage tanks need regular inspection, testing and cleaning. “Fuel tank cleaning is one of the most important things an owner or operator of an underground or above-ground fuel storage tank can do to keep their fuel performing properly,” says Ryder’s Cochefksi. “In the past, it’s usually been on an ad hoc basis,” he says, only testing when “customers see slow flow conditions in dispensers because filters are plugging up. But customers are being more proactive.”

The Right Fuel Filters

The last line of defense is the filtration on your vehicles, so it’s important to get it right. The first step is to make sure you’re using a fuel filter that meets minimum engine maker specs. Maverick USA, the Arkansas-based flatbed carrier, does that and more. VP Mike Jeffress explains:

“First we start off by reviewing OEM specification requirements for the fuel system of the unit we operate. Then we go to the market and research availability of product that meets or exceeds those recommendations. Then we work with suppliers that we wish to consider.” Testing is done, results are studied and then decisions are made.

The right filter will also depend on operational factors specific to your fleet as well as the minimum OE specs. “Most customers want to spend the least amount they can,” says Wix’s Rhodes. “What we’ve started doing is trying to educate our customers on [choosing filters based on] how you drive.”

The basic filter that would be just fine for linehaul operation with less-than-maximum loads, he explains, wouldn’t cut it for operations that operate in the mountains pulling heavy loads.

It wouldn’t necessarily cause any engine damage, he says, but it would mean more dirt building up in the filter and more frequent filter changes — enough that it could negate the money saved buying the lower-level filters in the first place.

“We target the size of the particle based on what causes the most wear to the fuel injection equipment, then design it to remove that size particle better than 99% of the time,” Bretell says. “Only removing it 20% of the time just isn’t going to provide the performance for the fuel injection equipment.

"The key is not just a quality filter, because a lot of filters are quality, but high performance,” Bretell says. “What can it remove from the fuel and can it hold without letting it pass through over time?” Look carefully at filter claims of what size particles they remove. Even a screen door will catch tiny particles some of the time.

Historically, he says, fuel filters have had a tendency to allow some contaminants to pass through even after they were initially captured, due to filter loading conditions (when the filter’s getting full), pressure surges at engine startup, and vibration (think about how a flour sifter works). That wasn’t really a problem until the tighter tolerances of the high-pressure common rail engine, he says. “We cannot allow some of these contaminants to drift past the filter.

So, fuel filters and the media inside them have become more sophisticated right along with the fuel systems. “Even though fuel filters are tasked with removing smaller contaminants than ever before, with improvements to the media we’ve actually managed to increase contaminant holding capacity and flow,” Bretell says.

That leads to the question, how much longer can I go between fuel filter changes? Maverick’s Jeffress says opting for an additional pre-filter system on top of the standard OE filtration has extended filter change intervals, from 8,000 miles back in the ‘80s to 60,000 miles on OE systems, and 100,000 on pre-filter systems themselves.

Filter change intervals also can vary depending on the cleanliness of the fuel being filtered – which takes us back to making sure the cleanest fuel possible is put into the truck in the first place. 

What’s that black stuff in my filter?

If you cut a fuel filter open to see why it plugged early, or can see the filter media through the clear bowl of some fuel filters, you might see the media has turned black. It could be one of two things:

1. Asphaltenes. A naturally occurring hydrocarbon, these do not cause harm to the engine, according to Russ Bretell, manager of education for Cummins Filtration. In their smallest state they pass through the filter and burn. If the temperature of the fuel rises enough, these microscopic hydrocarbons start to stick together, or agglomerate, and can be removed by the filter. They’re shortening the filter’s life but not causing harm. They can be treated in storage tanks with asphaltene conditioners.

2. Microorganisms. These may enter a storage tank through the air vent or filler cap and can live right where the water at the bottom of the tank settles out and meets the fuel. A fuel delivery to the storage tank can stir them up and then they end up in the truck’s fuel tank and clog your filter. They can be treated in storage tanks with microbiocides.

Obviously, you need to know which is which so you know what treatment to use. While regular testing will keep you apprised of what you might have in your bulk storage tanks, it’s relatively easy to tell the difference on your filter, Bretell says. Although both asphaltenes and bioorganisms will look black and shiny, the nose knows.

“If you smell the filter when you change it and it smells like diesel fuel, it’s asphaltenes,” he says. “If it smells horrible, it’s microorganisms.”

About the author
Deborah Lockridge

Deborah Lockridge

Editor and Associate Publisher

Reporting on trucking since 1990, Deborah is known for her award-winning magazine editorials and in-depth features on diverse issues, from the driver shortage to maintenance to rapidly changing technology.

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