However, keep warm-up time to the minimum required. "Warming up the engine uses fuel with no resulting mileage, and therefore has a negative effect on fuel economy," says Gervais. Warm-up time should be minimized to just enough to ensure proper operation.
In fact, any idling is detrimental to fuel economy. "Depending upon the amount of auxiliary drive load on the engine, it can consume anywhere from 1/2 to 1 1/2 gal. of fuel per hour," says Powers. "Fuel economy improves up to 4% with a reduction in idle time from 50% to 25%. Excessive idling wastes fuel, adds contaminates to the oil and adds carbons to the combustion chamber of your engine."
Remember that cooling fans also consume horsepower, which reduces fuel economy. "Under normal operating conditions, leave the fan switch in the automatic mode while driving, which allows the fan to activate only when needed," says Powers.
Strike the proper balance
"Correct entire vehicle spec'ing is the second major area of fuel consumption performance," says McKenna.
You need to carefully evaluate the trade-offs. "Spec'ing is a balance between performance and fuel economy," says Powers. "Vehicles must be spec'd to meet the startability and gradability requirements for a given application. But these requirements must be met while maximizing the fuel economy potential of a given vehicle. This requires that the engine be spec'd to operate at the lowest engine speed at cruise as possible, while meeting the performance requirements of the vehicle."
Powers adds, "The Truck Maintenance Council has stated you could see up to a 3% reduction in fuel economy in vehicles spec'd to run 100 rpm higher than the engine manufacturer's recommendation."
Tire selection has a major influence on fuel economy. "Careful selection of tires that are made for the application with the least amount of rolling resistance can improve fuel economy by up to 2% over standard tires," says Gervais.
"Deep lugs have better traction, but have high rolling resistance," Powers notes. "Shallow lugs reduce the tread depth to decrease the rolling resistance. Ribs sacrifice traction, but offer lower rolling resistance and better fuel economy."
Tire choice really needs to be weighed against the specific duty cycle to determine the best overall value. "A highway tread may offer the lowest rolling resistance, but you can easily get stuck on a jobsite. Conversely, a severe-duty lug tire that sees very little true off-highway work may last forever, but it has nasty rolling resistance," says McKenna. Thus, it pays to consult a tire expert.
"Truck weight is also an important factor," says Gervais. "Each 1,000-lb. reduction in weight can save between 1% and 1.2% in fuel, depending on terrain. Therefore, it is important to 'right size' the vehicle for the application. Don't over-spec the truck."
Size engines to the task
Perhaps one of the most critical truck specs is engine selection. Too small or large an engine will result in decreased efficiency.
"If you purchase a larger engine than required, the engine's efficiency may not allow for maximum fuel efficiency," says Powers. "Likewise, if you select a smaller engine that must operate outside of its optimum operating range and load factor, it may not provide optimum fuel economy for a given application."
"Larger, higher horsepower engines will burn more fuel due to the driver inputs," Nycz explains. "Let's face it, if a bigger engine gets you to the top of a mountain at a higher road speed, you will take advantage of it, thus burning more fuel than with a lower horsepower engine that will take longer to pull the same hill.
"That being said, there is some merit to spec'ing the right horsepower and torque combination for the job," she adds. "If the driver feels he has adequate power, he's usually less aggressive. This results in better mileage through enhanced driveability."
It really boils down to understanding the power requirements. "In most (not all) vocational operations, torque is much more significant than horsepower," says McKenna. "Low-end brute power, a.k.a. torque, is really what allows the work to be done in extreme conditions."