With diesel prices at record highs, it pays to take steps to optimize fuel economy for your vehicle fleet. A good starting point is driver training.
"Of all of the factors that affect fuel consumption, drivers have the most influence on fuel economy," says Matt Gervais, heavy-duty product strategy manager, Sterling Trucks.
"Operators typically influence overall fuel economy by as much as 35%," says Christy Nycz, Cummins. "Operator training and implementation of electronic control module features [i.e., road speed limits] are key to reducing this disparity."
Gervais recommends training drivers to anticipate road speed changes; plan routes to minimize stops; avoid unnecessary engine idling; minimize accessory loads on the engine (air conditioning, fan-on time, etc.); keep rpms low and running in the "sweet spot"; optimize shift points; and use cruise control wherever possible. "Drivers who are trained in these techniques can improve fuel economy by up to 35%," he adds.
Speeding dramatically increases fuel consumption. This is especially true for vocational trucks, which exhibit many aerodynamic inefficiencies vs. their over-the-road counterparts. "The losses [in fuel efficiency] are somewhat greater due to the lack of aerodynamic aides and the irregular loads typically hauled by vocational applications," says Nycz.
Slowing down even a little can have an impact. "Slowing speeds by 1 mph on a vocational vehicle can result in a 2% to 3% fuel savings," says Gervais, "and slowing speeds by 5 mph can result in a 10% to 15% fuel savings."
Rapid acceleration should also be avoided whenever possible. "Instead, utilize a progressive shifting technique," says Mike Powers, global on-highway product development manager, Caterpillar. "Operate in the highest gear possible. Do not run one gear down unless operating in conditions requiring it in off-road applications." Keep the engine below 1,500 rpm (unless you have a heavy-haul application with a truck spec'd at 1,600 rpm), and downshift around 1,100 rpm.
Throttle applications should be smooth. "When accelerating, pretend there is a raw egg between your foot and the throttle pedal and the goal is not to make a scrambled egg," suggests David McKenna, powertrain products marketing manager, Mack Trucks. "There are exactly zero good reasons to give 100% throttle input to a Mack MP Series engine, whether from a start or even accelerating to pass."
He points out, "Every single time you accelerate at full throttle to well above 1,600 rpm ? even for a few seconds ? throw a quarter out the cab window, as that is your real return on fuel economy."
McKenna advocates watching your shift points. "Generally speaking, anything above 1,600 rpm turns very expensive diesel fuel into noise," he points out. "There is not much to be gained from engine braking vs. service brakes... The idea here is to avoid being constantly heavy on the throttle and on the brakes. Allow a distance between vehicles so you can coast or cruise."
"While coasting in gear, the engine consumes zero fuel," explains Powers. "Rather than braking hard for stops and/or exit ramps, back out of the throttle early and allow the vehicle to coast as far as possible. The rotation of the drivetrain will keep the engine rotating and all of the fuel pumped to the engine will be returned to the fuel tank. Once the engine goes into idle rpm, it will start burning fuel again. Any distance you can coast in gear is completely free mileage."
The influence of temperature
"An engine always performs better at operating temperatures," says McKenna. "However, there are many different weather zones, so differing practices should be used that are practical for your area. After a good cold soaking over a weekend, I would be inclined to allow the coolant temperature to reach approximately 100° F before moving. Where the climate may be somewhat more favorable ? anything above 40° F ? [move] as soon as the oil and air pressures have stabilized."