Maintaining MPG
You bought your vehicles for productivity and, most likely, fuel efficiency – and
proper maintenance will ensure you get your money’s worth.
By Paul Richards
It pays, literally, to remember that there are several, often-overlooked maintenance procedures and adjustments that can have a noticeable effect on fuel economy. That’s always been the case, but with sky-high fuel prices and ’07 engines on their way, it’s more important than ever that the work actually gets done. The return on investment for conscientious maintenance has never been better.
The powertrain
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Changing air filters on the basis of restriction-gauge readings is the most efficient method, since changing too often can cost as much as neglect. Photo: Peterbilt |
For example, engine manufacturers acknowledge that engine accessories can drink up to 18 percent of the fuel used to move a truck down the road. A spinning cooling fan alone uses about 20 hp. If the fan clutch is operating improperly – that is, not disengaging the fan when it’s not needed – that 20 hp is wasted pushing air, instead of helping to move the truck.
Speaking of pushing air, if a vehicle’s air compressor unloader is out of adjustment, the compressor can spend more time running than necessary, which uses extra energy and wastes fuel. “Air system leakage also will cause the compressor to run more than it normally would,” adds Scott Pearson, general marketing manager for Peterbilt. “And it doesn’t have to be a major leak.”
While everyone knows that a dirty air filter can deprive an engine of the air it needs for optimum combustion, and can result in less efficient operation, filter manufacturers warn against replacing air filters more often than necessary, since new air filters actually become more efficient (trap more dirt) with use. That’s because a porous cake of dirt builds up on the medium, reducing the size of the filter passages and catching more particles. Changing an air filter before this dirt-pie forms will allow more dirt to pass into an engine, causing faster wear. Also, the more often an air cleaner is changed, the more likely it is that contaminants will sneak in during the operation.
Changing air filters on the basis of restriction-gauge readings, says the Technology & Maintenance Council (TMC), is the most efficient method. TMC also recommends that gauges be removed periodically from air cleaners, and their operation checked with a vacuum pump.
“It used to be that a dirty air filter would cause an over-rich mixture and result in black smoke,” notes Tony Cook, a chief engineer at International Truck & Engine. “That would tell you it really needed to be changed. But today’s electronic engines will compensate for reduced airflow. They won’t smoke, but performance and fuel economy will suffer. The telltales are gone – you have to rely on restriction readings.”
When changing air filters, Freightliner recommends completely inspecting the air intake piping from the air cleaner to the engine. Look for loose connections, cracks, torn or collapsed hoses, punctures and other damage. Replace damaged components and tighten loose connections: You want to be sure the piping is airtight so all the intake air passes through the air cleaner.
Another good habit to get into, says International’s Cook, is to audit engine electronic control module parameters routinely. “Make sure your programmable limits, like maximum road speed, are still in effect.”
And drivers can be part of the picture. “If you don’t already have them, consider installing in-cab fuel mileage displays,” suggests Peterbilt’s Pearson. “If a driver can measure his performance, he can improve it.”
Fuels and lubes
In its “White paper on fuel economy,” Kenworth reminds fleet executives not to use engine, transmission or axle lubes that are of a higher viscosity than recommended for specific equipment and operating conditions. Higher viscosity lubes are thicker and harder for pumps and gears to move. That consumes more energy than necessary, and wastes a small amount of fuel.
Make sure fuel filters are changed at recommended intervals, maintains International’s Cook. “If they’re restricted, performance and fuel economy are reduced. Again, the old telltales, like a lean engine running hot, are gone.”
Also, if a damaged fuel filter allows contaminants to reach the injector nozzles, the fuel spray pattern will be disrupted, says Peterbilt’s Pearson. “That causes poor atomization, less efficient combustion and reduced fuel efficiency.”
As Mike Jeffress – vice president of maintenance for Maverick Transportation in Little Rock, Ark. – notes, “Air filter restriction, charge air cooler testing, waste gate settings and fuel filter intervals … if you can keep your hands around these items, generally speaking, fuel economy will be pretty decent.”
And when purchasing fuel, don’t forget about quality, adds Chuck Livering, service engineer for Volvo Powertrain, a supplier of engines to Volvo and Mack. “The wrong specs for cetane, viscosity, specific gravity, etc. can hurt performance, fuel economy ... and your engine.” Minimum satisfactory specifications for diesel fuel can be found in TMC’s Recommended Practice 304B (http://tmc.truckline.com).
Tire considerations
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Fleets with a rigorous tire-pressure-check program enjoy better fuel
economy and longer tire life. |
According to tire manufacturers, tires can contribute, through rolling resistance, as much as 35 percent to level-road fuel consumption. The good part is that, where tire maintenance is concerned, what’s good for fuel economy is also good for tire life. That includes matching tires in size and maintaining proper air pressure all around.
“Some fleets may fail to reduce the rolling resistance of the equipment by not matching tires,” says Duke Drinkard, vice president of maintenance for Southeastern Freight Lines, based in Columbia, S.C. “We make sure tires match, in terms of both air pressure and size.”
The relationship between inflation pressure and fuel economy is simple: Underinflation equals increased rolling resistance. A soft tire deforms to a greater degree as it rolls against the road. So, more energy is used bending the tire’s belts and flexing its sidewalls. That’s energy that could be put to use racking up miles. Gross underinflation is estimated to cost between 3 percent and 5 percent in terms of fuel economy.
Also, an underinflated tire, with its exaggerated deformation, runs hotter, much as a paper clip gets hot when you bend it back and forth. And since heat degrades a tire’s casing integrity, a softer, less fuel-efficient tire is likely to have a shorter service life. This is true for all tires, new or retreaded, according to the Tire Retread Information Bureau.
TRIB adds that roughly half the scrap rubber found on highways – the result of casing disintegration from running underinflated – comes from tires that have never been retreaded.
Wheel alignment
Wheel alignment is a more complicated issue. When the wheels on a vehicle don’t all agree on what direction to travel, they fight each other, removing a little rubber with every revolution. Fuel economy suffers because it takes extra energy to erase tire tread. In fact, even slight misalignment, say tire manufacturers, can result in a 1 to 2 percent fuel economy penalty. “It’s using fuel to waste tires,” observes International’s Cook.
Although the term “front-end alignment” has been around for a long time, opportunities for misalignment are not limited to the front end. So think of rear and trailer axles as added opportunities to save precious fuel.
Don’t be a drag
Finally, OEMs agree that aerodynamic devices, such as air shields and fairings, should be kept in good repair. If parts are broken or missing, “you’re not getting the aerodynamic benefit you paid for, and, depending on the type and extent of the damage, you could be creating more drag than if the devices had never been purchased,” says Peterbilt’s Pearson.
And the same can be said of standard body panels, such as fenders and hoods. “Even moderate body damage can disrupt air flow around a vehicle and increase wind resistance,” says Mack’s Livering. “It looks bad, hurts your image and hurts fuel economy.”
Choose lubes wisely
The right lubricants can help maximize fuel economy
The right lubricant can help with fuel economy in several ways, says Mike Lynskey, heavy-duty products technology manager for Castrol/BP. “Most importantly, it does so by reducing the internal friction within the engine.“ Performance in both cold starts and normal temperatures is important, Lynskey says. ”And, ideally the lubricant should have an excellent ability to control thickening caused by soot and degradation, as this will maintain fuel economy well into the drain interval.”
“For today’s engines, it is of the utmost importance to use a lubricant that resists oxidation and properly controls soot,” maintains Greg Croce, North America product line management for Chevron Products Co. Oil thickened by soot requires more power to pump through the system, resulting in lower fuel economy.
“More important than engine oil in maintaining good fuel economy is the role of drivetrain lubricants,” Croce adds. “Lubricants used in transmissions and axles can become oxidized and thicken, causing increased drag or resistance on the drivetrain, resulting in direct reduction in fuel economy”.
According to Mark Betner, heavy-duty motor oil manager for Citgo, a lighter viscosity engine oil takes less energy to push around, and can provide improved fuel economy. After all, “Why does the automotive market recommend or factory fill with 5W-20 or 5W-30?” Betner adds that in Europe, 5W-40 and, more recently, 5W-30 is popular because they have been dealing with higher fuel prices for some time.
“The fact is that more and more fleets have tested and evaluated a 5W-40 option to the more popular 15W-40 and have reported as much as a 2 to 3 percent improvement in fuel economy,” Betner says. With improved cold fluidity and engine lubrication protection at startup, 5W-40 is worth a look, he says.
According to David Taber, senior scientist for ConocoPhillips, 76 Lubricants brand, fleets should specify a premium motor oil that will maintain its viscosity throughout its drain interval. “Too low of a viscosity, and engine wear will accelerate,” he says. “And if viscosity is allowed to increase, excessive friction will occur, causing a reduction in the engine’s fuel economy.” Taber also advocates using high-quality, synthetic drivetrain fluids to reduce internal friction, which translates to improved fuel economy.
A fresh oil change will improve fuel economy, but “Degradation of oil between drain intervals equals a degradation in fuel economy,” asserts Alex Bolkhovsky, commercial vehicle lubricants technical adviser for ExxonMobil. “Synthetics are best at resisting degradation for a full, extended drain interval.” He adds that the biggest gain from synthetics comes from use in the drive axle, with the second-biggest gain in the transmission, and the third in the engine. "They’re individual decisions based on a cost/benefit analysis,” Bolkhovsky says.
“Properly selecting the correct gear oil can favorably impact fuel efficiency,” says Dan Arcy, technical marketing manager for Shell Lubricants. “That’s why it is important to use the optimum viscosity-grade gear oil for the temperature in which you are operating. For example, an SAE 75W-90 viscosity may be the better option versus an 85W-140 grade because the flow rate will improve, especially at startup and in colder temperatures. The higher grade requires more energy to pump the oil and to get it to flow through the system. Before making any changes, however, you will want to make certain that the OEM approves of the lower viscosity.”
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