Good fuel economy means not straying from your goal.

Trucking 202
March 2000

Topic: Fuel economy

Keywords: fuel economy, speed, aerodynamics,

Driving for Dollar$

Fuel cost is a killer, but you’ve got ways to fight it — and put thousands of dollars in your pocket.

By Jim Park

Can anything be done about the rising cost of fuel? Unless your cousin is related to the chauffeur of an influential OPEC oil baron, the prospect of influencing the price of crude oil is pretty slim. But you can certainly lessen the pain.

It may be easier said than done after years at the wheel, but the quickest fix is to adopt a more conservative approach to the way you drive. No expensive add-ons, no time-consuming training sessions, no snake oil. Just an attitude adjustment.

How much impact can driving habits have on fuel economy? Depending on how you’re doing now, about $10,000 a year isn’t out of line, with almost no effect on your day-to-day operation. Smarter driving can earn you an increase of almost two miles per gallon, and we’ve proven it (see sidebar, ‘Saving Fuel In the Real World’).

The Sound of Money

From a personal perspective, I’ve grown to hate the sound of an engine running anywhere above 1600 rpm. It just sounds expensive. When progressive shifting became an issue many years ago, I tried it, and found that the engine ran much quieter at the lower rpms and shifting was considerably easier as well. I had the benefit of some good training in the proper operation of a modern, electronic diesel engine, but don’t take my word for it. Here are some tips from recognized industry experts on how to spec an engine and more importantly, how to drive it.

The folks at Caterpillar refer to Jim Booth as a senior applications engineer. Actually, Booth is a small fleet owner who ‘test drives’ all of Cat’s prototype engines under real-world conditions in his own fleet. He’s also a recognized expert in fuel economy, and he says it’s as much a matter of habit as anything else.

“There’s no secret to it,” he says. “You just have to decide that you want better fuel economy and don’t stray from your goal.”

Booth says he’s heard many drivers say they have trouble getting used to the different sound the truck makes when it’s going slow, and a harder time still watching the scenery just crawl by. “But,” he says. “it’s particularly tough to ignore the ribbing you’re going to take for not running with the pack. These are all just habits, things you can change right now with no up-front cost, no modifications and no technology, just good old fashioned discipline.” Booth’s key fuel-saving tip? “Gear fast, run slow.”

That’s become a common idea, and a good one, but there’s a limit. Steve Bellinger, assistant chief engineer, vehicle engineering, at Cummins, says there’s absolutely no point in gearing a truck so it could run at 100 mph.

“You’ll get your best fuel economy if you use operating techniques that result in the lowest number of engine revolutions per mile,” Bellinger says. “But that doesn’t mean gearing the truck so high that you’ll have to run two gears back to keep it under 65 mph.”

The thing you have to remember about gearing is that transmissions are designed to create the least internal friction in top gear. According to Bellinger, running one or two gears back means you’re sending power through too many gear meshes, which is terribly inefficient .

Drive Your Spec

Alan Hertzog, supervisor of service training for Mack Trucks, says that better fuel economy begins with the engine spec. Its power curves indicate the engine’s performance characteristics, and by interpreting that information you can figure out how to drive it best.

Hertzog warns against spec’ing the engine for economy and then driving the daylights out of it. “Be realistic when you begin to spec the truck, and go with an engine that runs the way you’re going to drive it.”

You’ve also got to understand torque and use it to your advantage. “Torque is what gets you moving and keeps you pulling under load,” says Dwayne Barnett of North American Truck Training Center in Brantford, Ont. He’s also a contract driver trainer for Volvo Trucks Canada. He says there’s much to be gained from judging accurately when to shift on a hill.

“It’s a judgement call whether or not to drop a gear right away,” Barnett says. “If you think you can pull the hill without shifting, go for it. But sometimes it’s better to drop a gear just as you begin to climb, then let torque do the rest.” Be careful to avoid dropping below the peak torque point though; things will begin to fall apart pretty rapidly after that. You may find yourself having to grab two gears instead of one on the next downshift.

The Boost Gauge

One of the most under-utilized fuel-saving devices on a truck today, according to Chuck Blake, staff application engineer at Detroit Diesel, is the turbo boost gauge, sometimes called the intake manifold pressure gauge. Not many trucks have these gauges any more, and that’s unfortunate.

Burning fuel produces exhaust which spins the turbocharger, forcing air into the intake manifold. Excess intake manifold pressure means you could be burning more fuel than you need. Blake says there’s seldom a reason to push the boost pressure any higher than 15 psi. “If you’re getting up past that mark, you’re being too aggressive with the throttle,” he says. “Use the boost gauge as an indicator of how much throttle you need to maintain modest acceleration.”

Blake also says that in some situations, cruise control can actually cost you money. “Cruise control is a fairly aggressive throttling mechanism. It’s designed to keep the truck at a steady speed, which the computer may decide requires a full-throttle application,” he says. “A driver can usually out-do cruise control for fuel economy by simply letting up on the pedal a bit when climbing a rolling hill. Ask yourself if you really need to hit the top at the preset speed?”

The bottom line in all this? You can’t suck and blow at the same time. If you want to go up and down the road like Jack the Bear, today’s engines will deliver. If you’re thinking in terms of maxing out your RRSP at year’s end, today’s engines can help you do that too, but you can’t do both. What becomes of your hard-earned money is pretty much up to you.