What contributes to fuel mileage in a semi-truck? Many people think it’s always the engine, change one part on the engine and miracles are supposed to happen and yes if everything else is right on the complete rig, fuel mileage will improve. In general there are two sides to this equation. The most common question we get here always starts out the same way; "What will my fuel mileage be if I..." This question cannot be answered accurately without knowing both sides of the equation.
The first side of the equation involves the engine. This is where a truck transfers the chemical energy from the fuel in its tanks to rotational mechanical energy in the engine to kinetic energy as the whole truck builds momentum as it accelerates down the road. The more efficiently your engine converts this energy from one type to the other, the more you'll save in fuel. It's this side of the equation that we at Pittsburgh Power specialize in. Most of our articles deal with ways to generate more power with less fuel. This is only half the battle to get great fuel mileage. In this month's article we are going to talk about an important part of the other side of the equation generically known as drag.
Drag is the only thing stopping your truck from rolling on forever after you get up to speed. Most people simply know of drag as a force that opposes movement and robs energy. There is a little more to it than that. Just like your engine doesn’t make energy but converts it from one form to another, drag doesn’t truly rob energy. It converts kinetic and mechanical energy to heat. There are no exceptions to this. The more kinetic and mechanical energy your truck and trailer generate, the stronger the drag gets and the faster the force of drag converts your energy to heat. What’s the easiest way to tell if your wheel bearings are starting to fail? Just put your hand on the hub and feel for excess heat. The higher drag from a failing wheel bearing generates more heat than a bearing that’s healthy.
When a truck is pulling a trailer down the highway between the tires, the wheel bearings and aerodynamics, up to 65% of the total drag is produced by the trailer. So think about your trailer. If your trailer’s tires are not the low rolling resistance type, the wheel bearings are set too loose, the axles are not in alignment with the king pin, the load is heavy on the trailer axles, the gap between the back of the bunk and the front of the trailer is more than 36 inches, or the load is wide, has lots of openings, bull racks, or hay haulers the drag will add up quickly and drastically. The Wind Blocker will increase the fuel mileage by about ½ mpg or more to a van or reefer trailer or a flat or drop deck with a roll tarp. There you go, a roll tarp will decrease the fuel mileage by ½ mpg and now you can get it back with the Wind Blocker. The Wind Blocker mounts to the front of the trailer and is adjustable and blocks the wind from the front of the trailer.
If you pull a company trailer there isn't much you can do to fix this problem. When it's your trailer work with it. The improvements you make will pay you back in fuel savings. Stop by MD Alignment Service in Des Moines Iowa, and if you get the chance to speak with Mike Beckett do so. Listen to what he has to say, he'll show you how to check your tractor alignment with a piece of string, tape measure and a piece of tape.
Now let's talk about the tractor again. Mike Beckett will tell you how to properly set the wheel bearings, and let them do an alignment on your tractor, you will feel the difference. Are the tires on the tractor the low rolling resistance type? If so, you will have to call the tire manufacturer for the resistance spec, I do not have them. How are you geared? If you have a 13 or 18 speed transmission you can be at your prime RPM all the time. If you have a 10-speed transmission, it's not always possible because of the 500 to 600 RPM gap between the gears. What about the rear gears? 3:36 usually puts the truck in a lugging mode most of the time and are the hardest gear ratio on fuel mileage. We prefer 2:64 gears and run the transmission in direct gear most of the time. Many people think they will lose pulling power on the hills with the 2:64 gears; however that is not true, you will gain power because the transmission is in direct gear and will deliver more power to the differentials because of a reduction in drag.
Back to the engine, yes we can gain 1 mpg or more if your truck is equipped with an Acert Cat and a DPF. It's a lot of work to fix this engine, however it's possible. We have taken a 2008 Pete with the Acert Cat and DPF and improved the fuel mileage from 4.2 to 6.7 mpg at 70 mph, if he drives by the turbo boost gauge the fuel mileage will go to 7.3
The DD5 Detroit with EGR is easier to fix than the Acert Cat, and the fuel mileage will improve by 1 mpg and no more problems. Likewise with the ISX-EGR and the ISX-EGR-DPF, all can be fixed. There is no magic wand, it takes a few days in the shop and parts need to be installed.
The 2002 and older engines require less work to produce power and fuel mileage; however don't get discouraged if you love new trucks, they can be fixed also.
Written by Bruce C. Mallinson and Fernando DeMoura, Pittsburgh Power Inc., 3600 S. Noah Dr. Saxonburg, Pa. 16056. Phone 724-360-4080.
|
