Do a Google search of how to improve mileage and you get a ton of hits of pages hawking the latest scientific miracle breakthrough, which has been suppressed by Evil Incorporated. Most of them are-how to say it?-scams based on junk science. Some are loosely based on sound science, but offer no measurable increase in fuel efficiency. Then you get into the real actionable intelligence, which we'll go into detail here.
We'll start with the aspect of the fuel consumption that you have the most control of, or at least should: your behavior as a driver. After that, we'll address the state of repair and tune of your ride and how they impact mileage.
Where Your Ride Burns its Fuel and What You Can Do About It
According to the Society of Automotive Engineers (SAE), the energy consumed by a vehicle when driven falls in three basic categories: 1. work due to (aero) drag; 2. work due to rolling resistance; and 3. work due to acceleration. The EPA estimates that in a typical drive cycle, your vehicle uses energy in the following manner:
- Stop-'n'-go city driving: 60% of your fuel is used to accelerate, 23% is used to overcome rolling resistance, and 17% is used to overcome aerodynamic drag.
- Highway driving: 43% of your fuel is used to push through the air, 30% overcomes rolling resistance, and 28% is used to accelerate.
- Combined city/highway driving: 45% goes to acceleration, 29% to overcome aero drag, and 26% to overcome rolling resistance.
A free-flowing exhaust system is one of the more effective mileage-enhancing mods you can
What this means is, first of all, you're screwed in stop-'n'-go traffic. You burn a lot of fuel accelerating your truck just to slow it down and stop. And when you're stopped and idling, you get zero miles per gallon. About the only thing you can do is to try to accelerate smoothly, find a pace that will allow you to flow with traffic, and all with the least amount of stops.
In highway driving, you have more control. And the factor that has the greatest influence on energy consumption on the highway is speed. This is because most of your fuel is used pushing your truck through the air. And check this out: The fuel required increases at the cube of the speed. Want an example? Here's how the EPA breaks it out at 40 mph and at 55 mph:
- 40 mph: 48% of fuel consumed by aero drag; 52% by acceleration
- 55 mph: 64% of fuel consumed by aero drag; 36% by acceleration
What this means is you have to slow down in order to improve fuel mileage, assuming all other things remain equal. At 40 mph you're using more fuel to accelerate to speed than you are overcoming aero drag. At 55 mph, you're using more fuel to overcome the drag. And aero drag increases at the cube of the speed. So, if you're traveling 55 mph and you speed up to 70 mph to change lanes, your fuel mileage really takes a hit compared with if you slowed down to allow the other vehicles to go by to change lanes.
To recap, you need to drive smoothly and try to pace the traffic in stop-'n'-go city driving, and keep top speed and accelerations to move through traffic at a minimum if you want to travel farther on less gas. Of course, we realize that sometimes we just have to feed the need for speed. We're not judging here; we're just trying to keep you informed of the cost involved.
Gas-Robbing Mechanical Repeat Offenders
Even the best driving habits cannot overcome poor maintenance. The repeat offenders that steal most of your fuel are loose or missing gas caps, broken thermostats, worn plugs, defective engine management components, under-inflated tires, and incorrect alignment.
It's not something that's readily apparent to most, but if your gas cap is loose, you'd be surprised at how much that's costing you. According to the Sept. '00 issue of Service Tech magazine, an estimated 17 percent of vehicles on U.S. highways have either incorrectly installed or missing gas caps, allowing approximately 147,000,000 gallons of gas per year to vaporize into the atmosphere.
But that figure, as impressive as it seems, is peanuts compared to driving with low tire pressure and your truck's suspension out of alignment. These two factors raise rolling resistance way above normal levels and simply drain money away from your wallet. Each of these conditions can take a mile per gallon of your average without you even knowing it. A slight misalignment and slightly low inflation pressures can really hurt your rig's mileage.
A couple of other factors that degrade your mileage, not usually associated with fuel efficiency are engine oil and the transmission. Dirty oil produces more friction, which, in addition to wearing your engine faster, reduces fuel mileage. If your automatic transmission isn't functioning correctly, it may be slipping or shifting improperly; both cases are bad for fuel mileage. And don't forget the thermostat. If the thermostat malfunctions and causes the engine to run slightly cold, the engine management system feeds in more fuel to make it run properly, and that reduces mileage. And finally, an improperly tuned engine can rob you of a few miles per gallon.
Add it all up and you could be losing several miles per gallon in efficiency from neglecting routing maintenance items. So go clean the air filter, get the engine tuned up, check the gas cap, and make sure your tires are properly inflated and that the alignment is correct. And at these prices, you'll probably recoup the costs in less time than you think.
Gauging Mileage Gains
If you're really hard-core, you can maximize fuel economy by monitoring gauges. By fitting a gasoline engine vehicle with a manifold vacuum gauge and keeping the manifold vacuum as high as possible while driving, you'll maximize mileage. For diesel-powered vehicles, Banks Engineering says that fitting them with a pyrometer to measure exhaust gas temperature (EGT) allows you to minimize fuel consumption by driving so the EGTs are as low as possible.
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