Maintain your fuel filter for the entire system’s sake
Diesel injection systems thrive on clean fuel. The “tolerances” – how snugly the parts fit together – are tighter in an injection system than any in medicine, the space program or any other field.
Tight tolerances are necessary because the system works under enormous pressure and also meters the fuel, which means it measures the exact amount going in each time each cylinder fires. The injector plunger is a small cylindrical part that slides through a long, tubular hole drilled inside the body of the fuel injector. When the plunger is forced down by the camshaft and a rocker lever, it pushes the fuel in front of it and can generate more than 30,000 psi. If much fuel were to leak around the plunger, it would not only take more power to generate the pressure, it would be impossible to ensure the right amount of fuel was getting pumped in each time.
Injectors work really hard. In a trip of 1,000 miles of continuous highway cruising, each injector will fire about 692,000 times. Firing means injecting an individually metered dose of fuel with the help of the engine ECM.
The plunger is not the only precision part. There’s also a tight-fitting needle valve and spring at the bottom of the injector that keeps the nozzle from dribbling fuel when the injector is supposed to be inactive. The injectors Cummins uses in the ISX don’t have needle valves, but they do have a double plunger system to handle both the timing of the injection and the metering.
And all injectors have extremely tiny holes in the nozzle at the bottom. These have gotten smaller and smaller in the last few years as injection pressures have risen. Research has shown, however, that the tinier the holes and the higher the pressure, the less soot the engine will produce and the better it will perform.
The top of the injector is lubed by engine oil. But the plunger itself and the needle valve are lubricated by the fuel they handle. And because of the tight tolerances and tiny holes, unless that fuel is absolutely clean, the moving parts will be scored or scratched and will quickly lose their snug fit because of wear, or the holes may clog. The plungers may even stick, which will stop an injector cold. So in order to protect injectors with tighter and tighter tolerances, finer and finer fuel filtration has come to our industry.
Primary and secondary filtration
Trucks have a mechanical fuel transfer pump on the engine that draws the fuel from the tank to the engine, then generates a pressure of about 40 psi to send the fuel to all the injectors. While the engine’s fuel pump is not as vulnerable as the injectors, it still could be easily damaged by water. So all engines use a primary fuel filter, which means a filter in the line leading from the tank to the pump. The fuel flows through this filter because of the suction generated by the fuel pump.
Filtration means moving fuel through a complex synthetic material, something like a very fine screen that grabs solid particles and holds them. The finer the screen, the greater the restriction it presents to the flow of fuel. So the engine and truck makers install a relatively coarse primary fuel filter on the suction side of the pump, where there is only suction, and add a very fine filter on the line running from the pump to the injectors, where there is plenty of pressure to work with. The primary filter removes larger particles that could damage even the relatively simple engine-driven fuel pump and, in many cases, is specially treated to remove water as well. Even though the very fine secondary filter may generate some restriction, the positive pressure generated by the pump ensures good flow unless it becomes thoroughly clogged.
Wix Filters’ manager of technical services and customer training, Paul Bandoly, likens the process to using sand paper to refinish a piece of furniture. You use coarse paper at the beginning of the process and move to finer and finer paper at the end. He calls the ultra-fine filtration of the latest secondary filters “polishing the fuel.”
The strategy is simple: “The primary gets the big stuff so the secondary will last longer.”
Steve Englund, senior project management administrator at Baldwin Filters, says a typical primary fuel filter is “rated at 15 to 25 microns absolute and is positioned prior to the fuel pump [suction side] to protect it from contaminants.” Secondary filters usually are rated at “three to ten microns absolute and positioned after the fuel transfer pump [pressure side] but prior to the injection pump or injectors.”
Donaldson’s Brian Tucker, engine liquid product manager, says primary filters usually “will have treated media to provide water separation performance. This can be either cellulose or a multi-layered synthetic media called melt-blown coupled with cellulose like Donaldson’s Synteq media.” Secondary filters usually are “an untreated cellulose or purely synthetic media. These differences mainly have to do with the water-separation requirements placed on primary fuel filters.”
Typical filters use media that are “pleated,” or folded in a zig-zag pattern to make pleats like a curtain. This squeezes more surface into the spin-on can, which extends filter life. A few filters come as cylindrical cartridges, which are installed inside a permanent filter housing after cleaning.
Today, “fuel must be drier than ever,” Bandoly says. Water can not only wash lubricating fuel off hard-working injector parts, its different flow characteristics can blow the tip right off an injector. It’s probably best to fit a primary filter that includes water separation capability, which means specially treated paper that keeps water from passing through, a reservoir to catch water and a drain.
Detroit Diesel offers the DAVCO primary filter and water separator, and most Series 60s are equipped with one, says Technical Service Manager Scott Faris. “Not all primary filters have water drains. Those that do have drains are typically called ‘primary water/fuel separators.’ They must have 93 percent minimum efficiency on emulsified water.” They need daily draining, Faris adds, easy to do “since most have a handy valve on the bottom of the filter.”
Bandoly agrees that daily filter draining is the way to go, at least until you see how much water you get. Do it in conjunction with your pretrip inspection. If you get no water, you are getting good fuel. If you get a coffee cup full of water, you’ve got a fuel maintenance problem.
Donaldson’s Tucker says, “The frequency that the primary fuel filter needs to be drained is ultimately dependent on the quality of fuel that is being used. Most OEMs recommend draining your water separator daily.”
Bandoly says to fuel up at the end of the day. Nearly empty fuel tanks sitting overnight cool and allow the moisture in all the humid air inside to condense into the tank. Refueling gets most of the moisture out before that happens.
He says you also should drain your fuel tank monthly, as most have a simple petcock these days. Drain before refueling so water is not stirred up and mixed back in with the fuel above. He recommends only fuel additives that “de-emulsify” water, which means combining it into large globs to help the fuel/water separator work. There are lots of great products out there that emulsify water so it will mix well with the fuel and pass right through the injectors, but they actually will defeat the purpose of a good separator.
Bandoly says every engine model and year has its own particular filtration requirements, calling the process “prescription filtration.” All the other industry experts we spoke with agree completely. Unless you use exactly the right primary and secondary filters for your particular engine, you invite trouble.
The reason for this is that injection systems differ in design, which means their requirements vary. Also, over time, the tolerances and micron ratings have become finer and finer in order to help meet emission standards. This rating refers to how small a particle a filter will catch with 97 percent-plus efficiency. The secondary filter must screen out anything large enough to fill the tiny gap between those close-fitting injector parts and cause scoring. The size, Bandoly says, can be “smaller than red blood cells, or two microns.”
A good example of the evolution of filter design is the changes for Series 60s mentioned by Scott Faris. “Secondary filters have different micron ratings based on the emission level and fuel injector technology of the engine,” he says. “For engines built before January 2004, the secondary filter must be 98 percent minimum efficiency on seven to nine micron particles. For engines built after January 2004, the emission levels are much lower, so the fuel injectors used are much more sophisticated. These sophisticated injectors use secondary filters that must be 87.5 percent minimum efficiency on three to five micron particles, 98.5 percent minimum efficiency on five to ten micron particles and 99.4 percent minimum efficiency on 10 to 15 micron particles.”
Baldwin’s Travis Winberg, supervisor of service engineering, says prior to 1995, “10-micron absolute filters were commonly used as the secondary or final fuel filter. However, with the advancement in fuel injection technology the majority of secondary or final fuel filters used on newer applications are five-micron absolute.”
Bottom line: Get the filter for your brand, year and model of engine. Bandoly insists you can’t even cut the filter apart to try and find a common design for several different engines. Filters that look exactly the same to the naked eye can be radically different in their performance.
“It is absolutely essential to use the correct fuel filters,” says Detroit Diesel’s Faris. “Injector warranties may be voided if the correct filters are not used.” Using the same brand and part number as the original is likely the “easiest way” to make sure you’ve got the right filter. Faris adds, “Detroit Diesel-certified repair shops are equipped to provide the same filters that came on the truck and can verify filter part numbers by using our electronic parts system.” The company publishes the “Lubricating Oil, Fuel, and Filters” brochure, listing correct part numbers for all Detroit engines.
Staying up-to-date on engine manufacturer recommendations also is helpful. “Use the product recommended by the engine manufacturer,” Bandoly says. “Go by an interchange or application guide.”
A reputable filter source “should be able to provide you with supporting data to ensure that their product indeed meets the filtration requirements set by the OEM for a specific application,” Baldwin’s Englund says.
When it comes to change intervals, all our sources agree engine manufacturers have sound recommendations. Read your owner’s manual and change as often as recommended. Filter clogging is often just a symptom of not changing at the proper miles or engine hours.
Bandoly points out that when switching to biodiesel, you should be prepared to change at least the primary filter more frequently for a few cycles because of the way this fuel loosens stuff that’s in the system and makes it come through with the fuel.
In the past, some truckers would install a finer, secondary-type filter on the primary side in order to save the secondary and make it necessary to change only one filter. It’s not smart to try it, says Baldwin’s Travis Winberg, who advises that “using too fine a primary filter shortens the life of the primary filter. Additionally, the use of a very fine primary filter may cause excessive restriction to the flow of fuel, resulting in poor engine performance.”
If you’re dead set on only changing one filter, there are high-capacity combination water separators and primary and secondary filtration systems available.
For more information:
Detroit Diesel Corporation