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Frequently Asked Questions about Diesel Fuel

Q: I’ve been handling my diesel the same way for years. Why should I change now?

A: You are not alone, with the exception of reducing sulfur content, fuel standards have not changed substantially in over a decade. Engines, however, have changed dramatically. In order for new equipment to run trouble-free, they require much cleaner fuel. This means an increased need for filtration. Manufacturers are insistent that damage caused by fuel contaminants is not a factory defect. Therefore, it is in your best interest to filter your fuel prior to use.

Q: Shouldn’t it be my fuel supplier’s responsibility to deliver clean diesel?

A: More than likely, your supplier is delivering perfectly in-spec diesel. The problem is that diesel cleanliness specifications are woefully out of date when compared to the needs of the modern engine. Some distributors are starting to go the extra yard and filter diesel prior to delivery, but this is not an industry requirement. An additional note of caution: the term “clean diesel” can also be used when referring to ultra-low sulfur diesel. This is not the same as reduced contamination levels or fuel “cleanliness”.

Q: How can I tell if my diesel is clean enough?

A: Testing is the only way to know how clean your fuel really is. Any reputable oil analysis lab should be able to help you with this, but if at all possible Donaldson advocates performing an in-field patch test. Compare your result (expressed by an ISO 4406 Cleanliness Code) with target cleanliness levels. Donaldson recommends ISO 14/13/11; below which point it is virtually impossible to distinguish in the field. Engine manufacturers do not accept liability for damage caused by fuel contaminants, so the cleaner the better.

Q: My fuel filters are plugging up really quickly; should I change brands?

A: It is important to use high quality fuel filters to protect your engine. In most cases changing filter brands will NOT solve your fuel problems. Remember, a plugged filter did its job. Rapid filter plugging is an indication that there is a problem with the fuel, not the filter. The key to resolving rapid plugging issues is to determine how filterable solids are getting into or forming inside your fuel tank, and then fixing the root cause. Switching to a lower efficiency filter, regardless of brand, will simply spread the problem throughout your fleet.

Q: The injectors and fuel pumps on my new equipment keep failing; what can I do?

A: The first step is to speak with your Original Equipment supplier. If you suspect that dirty fuel is behind the problems, a simple test can verify your fuel cleanliness level. Make sure you put the cleanest fuel possible into your equipment and protect your engine with a high-efficiency fuel filter. This should eliminate injector and fuel pump problems due to dirty fuel.

Q: Diesel is diesel, right? Why not buy from the cheapest source?

A: As with anything, you typically get what you pay for. Diesel is expensive, so it is tempting to minimize operating expenses by purchasing the cheapest fuel possible. While this fuel may meet minimum industry standards, that may not be adequate. Small differences in handling practices can have a huge impact on overall fuel quality and cleanliness. Saving a few pennies on your fuel bill may end up costing you far more in downtime, lost production and equipment repairs. Partnering with a good supplier is one of your best defenses against unforeseen fuel quality issues.

Q: I already have a 10 micron filter on my pumps; shouldn’t that be good enough?

A: Having a filter on your pumps is always a good idea. However, as modern engines have evolved, they need fuel that is hundreds of times cleaner than just a decade ago. Technology, such as 10 micron filtration, that was effective a few years ago is simply not adequate for modern equipment. With high injection pressures and clearances of only 1 or 2 microns in HPCR fuel systems, much tighter filtration is needed. As a rule of thumb, the filter on your dispenser should be just as efficient as the secondary fuel filter specified for your equipment.

Q: How can I tell if my coalescer is performing as well as the published test reports claim?

A: It is very difficult to determine the real time performance of your fuel water separator (coalescer). If no water is present in the drain bowl, it may mean either there is no free water in the fuel or that the coalescer may have decreased in water-removing efficiency. Additives and biodiesel in the fuel can decrease the effectiveness of the coalescer to remove water. Official test methods for water removal efficiency utilize fuel from which all additives and other surfactants have been removed, so test results are not an accurate predictor of real world performance with today’s diesel.

Q: I use a good cold flow improver, so why do I continue to have so many problems in the winter?

A: Cold flow improvers, by design, stop small diesel fuel crystals from growing into large diesel fuel crystals (also known as gelling). This in turn lowers the temperature at which the diesel can still flow and be used in the fuel system. With today’s HPCR engines, filters are becoming more efficient, and the smaller diesel crystals that used to pass through filters now get trapped just as particulates do. This can cause premature plugging of the filter and decreased life.

Q: Biodiesel was just introduced to my area. I’ve heard horror stories. What can I do?

A: While biodiesel has many good qualities, it can be a challenge as it relates to filtration. Biodiesel acts as a solvent, so it tends to clean the infrastructure when first introduced, putting a stress on existing filtration. Biodiesel begins to gel or solidify at much higher temperatures than petro diesel, making it difficult to flow and filter in colder climates. And finally, biodiesel contains glycerin, which even in small quantities can contribute to rapid filter plugging. Your best strategy is to remove any solidified glycerin before it reaches your equipment.

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