Diesel prices well in excess of a buck a litre appear to be the new reality for fleets and owner/operators in Canada. Survival in these trying times will hinge on your ability to recover fuel price increases from your customers and maximize fuel mileage as much as possible.

Much of a fleet’s fuel economy performance is ultimately in the hands of the guy or gal behind the wheel – but optimizing fuel mileage begins in the shop.

Simply put, a well-maintained vehicle performs better, and consequently achieves better fuel mileage, than a poorly-maintained truck. Here are a few tips owner/operators or maintenance managers can employ to improve their MPG.

Maintain proper tire pressures

One of the simplest ways to maximize fuel mileage is to keep tires inflated to the proper pressure.

“Tire pressure can significantly affect fuel mileage, and requires a closer inspection than a thump with a baseball bat,” says Ed Saxman, Volvo marketing product manager, drivetrain. “The time it takes to periodically air up all 18 tires to a recommended pressure is well worth it.”

For every 10 psi a tire is underinflated, a driver is penalized with a 1% drop in fuel economy.

Trailer tires have the biggest impact on fuel mileage, and yet these are often the most neglected tires on a tractor-trailer combination. Check tire pressures on tractors and trailers whenever they visit the shop and be sure to insist that drivers perform daily pressure checks to improve fuel mileage.

Check vehicle alignment

To get the best possible fuel mileage, it’s crucial the tires are pointed straight down the highway. “A tire that deviates only 1/4 degree from straight ahead will try to travel 10-15 feet sideways for each mile the vehicle travels forward,” according to Secrets of Better Fuel Economy a guide on fuel mileage published by Cummins.

Tests performed by Cummins show a tractor-trailer with a steer tire toe-in of 3/8″ and a drive axle that’s an inch out of alignment will punish fuel mileage to the tune of 2.2%.

It also causes premature tire wear, another unnecessary expense.

Inspect the fan

It takes between 10 and 70 horsepower to drive the fan on a heavyduty truck engine.

Typically, the fan will run 5-7% of the time the engine is on (depending on the time of year), but a problematic fan will run much more frequently.

Cummins Secrets of Better Fuel Economy says common fan problems include: an inoperative fan clutch; faulty thermostatic switch; or low coolant levels. Each of these can increase fan-on time and consume fuel unnecessarily.

About 50% of fan-on time is attributed to the freon compressor operation, according to Cummins. An overcharged system, defective or incorrect head pressure switches or a failed condenser can all cause fuel mileage to suffer.

Limit vehicle speeds

Setting an engine’s speed limiter is a simple process, and one that’s already employed by many of the best-run Canadian trucking companies. It soon may be law inOntario and Quebec, but it’s not necessary to wait until proposed speed limiter legislation is effective before taking action.

All engines built since the mid-90s have the capability – you simply need to plug into the engine’s ECM and manually set the desired top speed.

Slowing truck speeds from 113 km/h to 105 km/h improves mileage by about half a mile per gallon, according to Caterpillar.

The company claims fuel economy suffers about one-tenth of a mile per gallon for every 1 mph (1.6 km/h) over 55 mph (89 km/h) that the truck runs.

Check for air leaks

Leaks in a tractor-trailer’s air system can cause the air compressor to overwork, resulting in an increased horsepower draw.

A loaded tractor-trailer driven at 1,500 RPM will require 4.5 hp to operate the air compressor, according to Cummins.

That’s fine, but reducing usage of the compressor will noticeably save fuel.

Cummins states in its MPG guide that an air compressor should run about 5% of the engine run time with 10 to 12 minutes between cycles.

If it’s running more frequently than that, there could be a costly problem such as an air leak. Excessive operation of the air compressor can cause a 2% reduction in fuel mileage.

Gear fast, run slow

The gearing of a truck is particularly important if you hope to maximize fuel economy. Trucks spec’d for optimum fuel mileage should be set up to “gear fast, run slow.”

For instance, a Cummins ISX running line-haul with loads slightly less than 80,000 lbs would normally be geared to run at 1,450 RPM at normal highway speeds.

If geared for maximum fuel mileage, however, it will be set to run at 1,400 RPM in the top gears. Keeping the RPMs down at highway speeds is a good way to save fuel.

Transmission and rear axle ratios and even tire size are all part of the fuel mileage equation.

Unfortunately, trade-offs are sometimes necessary when gearing for fuel mileage.

Performance characteristics such as startability, torque, gradeability and cruise speed may be impacted by setting the gearing for improved fuel mileage. However, with the cost of diesel now hovering at $1.20/litre, those are trades that may be worth considering.

Fuel-saving maintenance tips from Kenworth

Kenworth has published a white paper on maximizing fuel mileage. Included are the following maintenance tips:

• Maintain tire pressure and check tire wear;

• Replace air and fuel filters at proper intervals;

• Keep axles properly aligned;

• Repair any body damage. That front corner of the dinged-up bumper hanging down hurts the vehicle’s aerodynamics and fuel economy;

• Use a good synthetic or semi-synthetic oil in the engine and drive axles. Also use a good synthetic transmission fluid;

• Don’t use a higher viscosity oil than actually needed for the operating conditions. n