With energy prices continuing to rise and no end in sight, fuel has become an even greater truck operating expense. Good fuel economy is the result of a combination of variables that, if managed effectively, can deliver the best fuel mileage possible for a particular truck.
The variables with the most impact on fuel usage include: aerodynamics, gearing, tires, load, speed, climate, idle time and driving techniques.
One of the most significant of these is the driver, says Jim Booth Jr., field service coordinator, Caterpillar Global On-Highway. The driver controls vehicle speed, shifting techniques, idle time, acceleration, brake usage, trailer gap settings and more.
Studies have shown that it is not uncommon for fleets with identically spec’d trucks to see as much as a 35 percent fuel economy difference between trucks — a difference that is solely due to variations in skills and attitudes of the drivers, he notes.
Advising drivers to lower their speeds, or governing trucks at lowered speeds, can help improve the number of miles a truck can drive per gallon of fuel. Horsepower demand increases substantially as vehicle speed increases.
“It takes a lot of power to push a large vehicle through the air, explains Booth. “A good rule of thumb to remember is that fuel economy will change about one-tenth of a mile per gallon for every one mile per hour over 55 miles per hour road speed change.
“In other words, decreasing overall road speed from 70 miles per hour to 65 miles per hour can improve fuel mileage by around half a mile per gallon.”
Actual fuel mileage increases will depend on the aerodynamics and weight of the vehicle. As speed increases, truck/trailer combinations with poor aerodynamics will experience greater fuel economy losses than those with better aerodynamics.
It is also advisable to develop measures for reducing engine idling. An idling engine can burn somewhere between half a gallon to one and a half gallons per hour, depending on the engine idle rpm and accessories in use, like the air conditioner, says Booth. Drivers can minimize warm-up times by idling only while doing the pre-trip inspection and filling out paperwork.
Once the coolant temperature gauge starts to rise off the peg, it’s okay to start moving the truck, he says. The driver should just be easy on the throttle until the engine reaches normal operating temperature.
The engine will warm up much quicker and the transmission, wheel bearings and rear end will warm up at the same time. Caterpillar has come up with its Top Five Driver Tips to Improve Fuel Economy.
1. Coast in gear whenever possible and for as long as possible
The objective here is to use the vehicle’s momentum and coasting ability. While coasting in gear, the engine consumes no fuel. A driver can take advantage of this coasting “free mileage” by backing out of the throttle earlier when approaching exit ramps or slower speed limits.
Down shifting a couple gears or so while coasting in gear to a stop or exit will get a driver the most “free mileage” possible. Backing out of the throttle at just the right time allows the vehicle to slow down to the proper speed while using a limited amount of braking, either with the service brakes or compression brakes.
2. Use progressive shifting
Progressive shifting keeps the engine rpm as low as possible. Progressive shifting means using only enough rpm to get into the next highest gear and still pull that gear.
For instance, in the low side of the transmission, a driver may be able to upshift at 1,000 rpm and still pull the next gear. When in the high side of the transmission, the road speed increases. Since the horsepower demand increases with the road speed, more rpm is required to upshift into the next gear.
A driver may be able to upshift at around 1,200 to 1,400 rpm while in the high side of the transmission. This depends on the load the driver is pulling. Heavier loads that pull harder than a lighter load require a little more rpm to get into the next gear and still pull that next gear.
3. Stay in high gear as long as possible
A driver should not downshift too early; only downshift when necessary. If a driver can get over a hill without falling below 1,200 or 1,100 rpm and not downshift, he should take advantage of it. Less rpm used to get over a hill means less fuel used.
A driver should let the engine do all the work, instead of working to keep the engine rpm within a certain range.
4. Limit idle time
Obviously, there will be times when idling the engine is a necessity. The trick is to concentrate on eliminating the unnecessary idle time. A good rule of thumb to keep in mind is that anytime a driver thinks he will be parked and away from his truck for more than five minutes, he should shut the engine off.
5. Slow down
The single most effective thing a driver can do to improve fuel mileage is slow down. Driving a little slower is also safer, extends tire life and minimizes the wear and tear on the truck, trailer and driver. Unfortunately, slowing down is also the last thing a driver wants to do.