When it comes to maintaining your trucks, the object is reliability and durability. You want your iron to give you uptime for a long time. But good maintenance also has a benefit on the fuel front.

Simple things like wheel alignment and fuel filters. When you add up their impact on your fuel bill, you’re talking about an excellent payback. There’s hardly anything on a truck that’s simpler than its air-intake system. And not really too many things that can have as much effect on fuel economy.

A diesel engine needs an easy flow of very clean air in order to function properly, and there’s as much as a two percent difference in fuel-efficiency at stake. Doesn’t sound like much, but for most over-the-road folks that’s going to be more than $1,000 a year.

Air intake is one of those things that you don’t normally have to worry about spec’ing when you buy a new truck. The engineers have it pegged. But if you switch from a nice clean highway haul to pulling gravel out of a quarry and then down a few dirt roads to the highway, you’d do well to ask a question or two of the experts at your engine service shop.

And, as with many other components, if you buy a used truck, it makes sense to find out if its air filter is the correct one — meaning sized properly to your engine — and if it suits the kind of work you’re doing.

AIR RESTRICTION

There might be one small spec’ing decision: most trucks come with air-restriction gauges, but make sure of it. You absolutely need it, because you can’t just look at a filter element and see that it’s dirty.

It may look like it’s kaput when in fact it has lots of life left. Only the gauge would tell you. The filter could also look clean enough to keep, but in reality be overloaded with fine dust. Again, only a restriction gauge could give you the true picture. 

It goes without saying that extra vigilance is required
to maintain a clean air supply in dirty, dusty conditions.

The gauge could be mounted in the dash (preferred) or under the hood, in the piping between the filter canister and the engine. Usually it’ll be a bar-type readout that shows restriction in inches (of water). It means ‘restriction’ literally — the difficulty that air has in getting through the filter, past the trapped dirt, and into your engine.

The contaminants involved are ordinary dust, carbon soot from the exhaust, and water by way of rain or snow or even fog. If dirt particles are ingested into the engine, they’ll do nasty things like damage the cylinder liners.

A normal restriction reading is 10 to 15 in., and as it moves to 20 in. or so it means there’s dirt plugging things up. The gauge will probably go up to 30 in., but the element needs changing at about 25 in.

Leave it longer and the engine won’t be breathing very well, and fuel economy will suffer. You’ll use two percent more fuel at 30 in., compared to 10, according to the Technology & Maintenance Council of the American Trucking Associations (TMC).

There’s not just dirt to contend with in limiting restriction. The ducting has an important role to play here too. Add too many elbows and bends, and you’ll also add restriction, perhaps in significant amounts.

TMC says that an easy 45-degree bend will add a half inch of restriction, while a smooth-radius 90-degree elbow adds one inch. But create a sharp 90-degree bend and your restriction gauge will show an increase of two and a half inches.

So that’s clearly a spec’ing decision too, though it’s only likely to arise if you’ve asked for some special equipment or made an oddball modification of some sort. Luckily, the ducting normally doesn’t travel very far, so there are only so many elbows you could come up with anyway.

The air-cleaner canister can be outside the hood on either side, or on both sides of a traditional long-nose/narrow-cab conventional. These days, with aerodynamic conventionals predominant, it’s more likely to be under the hood.

DRY FILTER TYPES

The dry system’s filter element, round or rectangular, sits inside a canister, and the system will draw air through the element and then into the engine. It can be mounted either directly on the engine or remotely.

The science of air cleaning has improved over the years, and these days most elements are very sophisticated things made of specially formed and treated paper or cellulose (sometimes a synthetic material as well), called the ‘media’. They’re sometimes re-useable, but with newer types this is less common. Make sure you know what you’ve got, because washing and re-using an element designed for one-time use will cause you grief.

If you do have a re-useable element, limit it to one year’s life and no more than six cleanings. Cleaning can be done by either compressed air or washing in a special solution. But take care if you’re using compressed air. That should be done cautiously by limiting the outlet pressure of the blow gun to 35 psi to prevent damage to the filtration media.

Most air-cleaning systems are single-stage mechanisms, but there are several two-stage types that have a pre-cleaner and a dust cup that collects contaminants before they reach the filter element itself.

Before you install a new filter element, make sure that you’ve got the right one. It’s possible to have the right diameter and the wrong height. It would fit, but there would be a gap between housing and filter, so the gasketing would never be able to make a seal.

And finally, every air-cleaning system must have a water-separating mechanism of some sort near the air intake. With an outside air cleaner, the intake should be mounted away from the flow of water-laden air as it streams over the hood or fender. That’s not always
possible, in which case a shield of some sort must be used.

There’s nothing complicated about any of this, at least not if you do it right.