Bottom Line
Got fuel mileage?
It's the little things that add up

By Jeff Barker
contributing writer


Anyone who’s been alive and breathing during the past few years knows that fuel costs have skyrocketed. Profit margins are becoming thinner for even the most business-minded truck owners out there. And there’s obviously not much, if any, relief in sight.

There are, however, many things you can do to help reduce the impact of high fuel costs.

Proper maintenance can play a big role in improving fuel mileage. Maintaining a few key areas of your truck will improve its operating efficiency and benefit your bottom line.

Engine overheads

Engines need an overhead done periodically as part of a good maintenance program. This includes adjusting the valvetrain and injector rocker arms. Scott Vanderheiden, service manager for Peterbilt of Council Bluffs, IA, suggests having this done every 100,000 to 125,000 miles.

An overhead helps the engine breathe better through the intake and exhaust valves and helps the injectors deliver a healthier shot of fuel into the cylinders. In addition to better fuel mileage, it will also benefit you in terms of pulling power on the hills and responsiveness when it’s needed. It will also help save your engine’s camshaft and other valvetrain parts from abnormal wear.

Air filters

If the air filters are clogged – even partially – your engine cannot breathe properly and will lose efficiency. Air filters and their restriction indicators need to be checked at every preventive maintenance and replaced as necessary, and they should be replaced at least every 100,000 miles on a dual air filter setup, or every 60,000 to 70,000 miles on a single air filter setup, according to Vanderheiden.

EGR valves

Most post-10/02 engines are equipped with exhaust gas recirculation valves that are part of required emission control systems. If the EGR valve becomes stuck or doesn’t function properly, it will cause increased fuel consumption and excessive exhaust smoke, not to mention a major loss of power.

Fuel injectors

In most cases, the average life of a set of fuel injectors is around 500,000 miles. Beyond that, the spray tips become worn and can’t provide a good spray pattern for proper combustion. After that much wear, the injectors also will likely be dribbling an unmetered amount of fuel into the cylinders, and that eats into your fuel mileage. To extend injector life, it’s recommended that you get the fuel filters replaced at every preventive maintenance interval.

Centrifugal advance

A few of our readers are understandably sentimental about their older trucks with those Cat 3406 mechanical engines. If those engines are maintained and operated properly, they can get decent fuel mileage.

Such engines have a centrifugal advance system that advances the injector pump timing as rpm increases. After a while it helps to get the system checked for proper operation.

Another item that needs occasional attention on the older mechanical engines is the air/fuel ratio control valve diaphragm. Many owners of these engines say that it makes sense to keep one in your toolbox in case you need to replace it on the road.

Charge air cooler

Over time, normal operating conditions can cause cracks in the charge air cooler, resulting in a loss of boost pressure from your engine’s turbocharger. If it’s leaking boost pressure bad enough, you will hear a loud whistling noise whenever your turbo “spools up” as it does under acceleration. Vanderheiden suggests getting it pressure-tested on occasion.

While we’re in this area of the truck, do yourself a favor and check the rubber boots and clamps in the intercooler plumbing. If any clamps are loose and/or rubber boots are cut or torn, you will have a power loss. That could cause some major embarrassment when an old Volkswagen camper bus blows your doors off on an uphill grade, and even more so when you sit down and run the numbers to figure out your truck’s fuel mileage.

Keep it clean

If the radiator, air conditioner condenser coil, and/or the charge air cooler fins are dirty or clogged with dirt, bugs and other stuff, it will cause your engine to run warm.

When the engine fan comes on as the water temperature gets around 205 degrees or warmer, it takes some serious power to run it, and that uses more fuel.

By keeping these items clean, the engine fan won’t come on as often, and as a result – you guessed it – less fuel is burned. Vanderheiden suggests cleaning these once a year.

Many drivers like to keep the engine fan turned on constantly when they idle their trucks for climate control. While it may be easier for them to sleep, doing that definitely increases fuel consumption.

If the engine runs below its optimum operating temperature from the fan being on more than necessary, it will burn more fuel, too.

Clutch adjustment

“Keep your clutch adjusted so it has good free travel, and a soft pedal (with about two inches of free play) so it does not slip,” Vanderheiden said.

If your clutch slips even just a little, it will kill your fuel mileage, not to mention that it will result in a premature and expensive clutch replacement down the road.

Axle alignments

“Keeping all axles on both your truck and trailer in alignment will result in less rolling resistance,” Vanderheiden said.

It also helps to prolong tire life. It’s advisable to have the alignment checked when new tires are installed, even when a truck or trailer is brand new.       

Trucks and trailers are notorious for having “rough” alignments done on them just to get them down the assembly line and out the factory door faster.

Tire pressure

This cannot be stressed enough. Becuase your truck’s tires probably are your second-largest operating expense, tire inflation should be checked with a gauge daily.

Neglecting this can result in more rolling resistance, causing lower fuel mileage or, worse yet, causing the adjacent tire on that hub to blow because of heat from excess weight.

Steer tires need attention, too. Just because your steer axle rims appear to be a few inches off the ground it doesn’t always mean you’re good to go. Just a slight variation in air pressure can cause irregular wear, not to mention causing the truck’s steering to pull to one side.

It’s a good idea – and required by the regs if you’re pulling a hazmat load – to get into the habit of checking your tires every time you stop.

If the tires were fine in the  morning, one tire could have picked up something during the day that could eventually result in a more serious problem. Your tire man will thank you for catching such problems at safe areas instead of putting him in a dangerous situation alongside busy highways.

ECM settings

“Make sure engine ECMs are calibrated properly for correct tire sizes and axle ratios, as well as optimum operating parameters,” Vanderheiden said.

You should get an ECM printout from each truck to monitor its operation and help identify problem areas such as higher than average road speeds, idle time, etc., and do whatever is necessary to correct the problems.


Aerodynamics play a huge role in terms of fuel efficiency. The less wind drag a vehicle has on the highway means the less fuel it needs to keep moving.

Most modern tractors – even Kenworth W900s, Peterbilt 379s and the newer 389s and other “big hood” models – usually have some sort of aerodynamic enhancement devices on them.

Whether it’s just a set of cab extenders or an air deflector above the sleeper that benefits those who pull van-type trailers, these items do provide a fuel efficiency benefit. If they’re damaged or missing, they obviously can’t do the job they were initially designed to do.

Many aerodynamic tractors with sloped hoods are also equipped with fuel tank fairing panels to help the air glide easily over that area of the truck. If any of those panels are loose or damaged and catching the wind, they will defeat their own purpose.

Bug Shields are nice to have, but even those with an aerodynamic design can cause enough wind drag to be detrimental to your truck’s fuel mileage.

If you’re planning to buy another tractor in the future, it would be wise to consider an aerodynamic model. Long-hood tractors look great, but, as they say, pushing that huge hood through the wind is like trying to push a brick through oatmeal. Also, what may be gained in resale value with those trucks down the road is likely to be quickly offset by the increased fuel consumption to operate one, especially nowadays.

If you pull a van type trailer and your truck has a sliding fifth wheel, you should close that gap between the truck and trailer to minimize wind turbulence between them. When weight and room allow, slide the fifth wheel forward to bring the truck and trailer closer together.

Add it up

No one thing is going to improve your fuel mileage 10, 20 or 30 percent. But the little improvements that each of these items contribute to your fuel mileage are sure to add up. If you’ve neglected maintenance of these key areas on your truck and trailer, you’re certain to see some improvement once everything is taken care of. LL


Editor’s note: This article is for information purposes only. If you’re not sure about performing the work yourself, it’s advisable to seek the help of a competent professional.

Jeff Barker is an OOIDA member and a former certified diesel mechanic. He can be reached at truckmaintenance