Hand Calculating Fuel Mileage (MPG)
Hand calculating your fuel mileage is the most accurate and precise way to get your actual fuel economy. To calculate your fuel economy, first fill your fuel tank and reset your odometer. Drive the vehicle until there is roughly a quarter tank of fuel left, then head to the fuel station and refill the tank. Record the the amount of fuel that was pumped, then perform the following calculation:
Fuel mileage in miles per gallon = miles driven/gallons of fuel consumed
Where "gallons of fuel consumed" refers to how many gallons of gasoline were required to fill your tank. For an added layer of precision, return to the same fuel pump at the same fuel station that you refueled at initially. Do not top off the tank; when the pump automatically shuts off, do not pump anymore fuel.
Fuel Economy Tips & Considerations for Truck Owners
Pay attention to your driving habits - More than anything, fuel economy is relative to the manner in which you drive. Hard acceleration and traveling at excessive speeds will have drastic impacts on your fuel economy. Accelerate at a rate that is light enough to avoid high engine speeds yet comfortable enough that you reach the speed limit in a timely manner. Keeping the engine speed under 2,200 RPM tends to meet this criteria for a V-8 engine. Obviously, towing completely changes the rules and higher RPM operation will be necessary at times when towing a trailer. Additionally, don't be afraid to coast when approaching stop signs and traffic lights. Coasting consumes very little fuel and using this technique to your advantage may impact fuel economy.
Follow a strict maintenance routine - Fuel economy diminishes with the condition of your vehicle's various fluids and filters. Air and fuel filter restrictions force the engine to work harder, producing greater parasitic losses. Worn spark plugs, distributor rotors, and ignition coils can reduce spark energy and promote poor combustion characteristics. Contaminated or old transmission fluid can effect an automatic transmissions shift schedule and performance, possibly leading to greater parasitic loss and poor efficiency. Always follow the OEM maintenance schedule and don't ignore the recommended procedures.
Switch to synthetic - Dino oils and service fluids are a thing of the past. There is little, if any opposition to the notion that synthetic fluids are superior and far more efficient than conventional petroleum based oils. While modern vehicles typically utilize synthetic oils in both the engine and drivetrain, older vehicles may benefit from a switch to a high quality synthetic. Don't forget the differential(s) and transfer case as parasitic losses can be minimized with more efficient fluids.
Roll down the windows AND run the air conditioner - Just not at the same time. Our own independent studies have shown that rolling down the windows while in stop-and-go traffic or traveling at low speeds consumes less fuel than running the AC in the same conditions. Likewise, running the AC at highway speeds seems to be favorable to having the windows rolled down. The reasoning is simple - the inherent downfall of the AC system is that the compressor places a load on the engine and therefore more fuel is consumed. The disadvantage of having the windows rolled down is that it produces greater aerodynamic drag at higher speeds, and the relationship between drag is exponentially related to speed; greater drag results in greater fuel consumption.
Therefore, the solution is to keep cool while avoiding the inherent problems (as much as possible) with each option. Roll the windows down while driving in stop-and-go traffic and at low speeds, as there is little drag regardless of whether the windows are down or not. At highways speeds, where drag becomes excessive, run the AC. While the AC compressor will place an additional load on the engine, the parasitic loss can be low at higher cruising speeds as a result of the engine RPM being closer to its peak torque range. Finding your vehicle's "sweet spot" may take some experimentation, as the results may vary considerably.
Shed some pounds - The heavier your vehicle, the more fuel the engine is going to consume. If you're driving around with items in the bed or cab that don't need to be there, simply remove them. You could theoretically remove the spare tire and jack, but we wouldn't recommend going that far for obvious safety reasons.
Reconsider the lift kit - Installing a lift kit and large tires is a popular customization that can give a truck a truly unique appearance. However, don't complain about fuel economy if you've gone and built yourself a mall crawler. Lifted trucks are terribly inefficient for a number of reasons. First and foremost, they're the aerodynamic equivalent of a brick; lifting a pickup greatly increases the cross sectional area of the vehicle, causing greater drag that must be compensated for by engine power. The second significant effect is the physical weight of larger tires. The centrifugal force of each tire and the frictional force between the road and each tire is greater for a larger tire and requires a greater amount of energy to keep moving.
Additionally, the effective final drive ratio is modified when larger tires are installed unless the ring and pinion of each axle are swapped to compensate for the change. The effect is the equivalent of replacing a 3.73:1 differential with a 3.05:1 one. On the contrary, a 4.10:1 or even 4.56:1 differential would need to be installed to compensate for this effect. The taller the tire, the greater the overall consequences. Replacing a 31" tire for a 33" tire, for example, will have less effect than jumping to a 35" or 37" tall tire. The higher overall ratio maintains low cruising RPM, but there is a point of diminishing return and the engine is going to experience more load with a taller final drive ratio. This effect is the reason that speedometers must be re-calibrated when tire size is changed. Everything in moderation; the more you jack it, the more your fuel economy will suffer.
Keep it under 55...or 65 - Aerodynamic drag depends greatly on velocity; the speed of your vehicle squared, to be exact. If you were to chart the total drag force on your vehicle with respect to the speed of the vehicle, you'd notice that the drag force rises exponentially, not linearly. It just so happens that 55 mph (~90 kmh) is generally considered the critical point on the drag curve. Since the drag force is rising exponentially, the difference in drag between 45 and 55 mph is significantly less than the difference in drag force between 55 and 65 mph. To put this in perspective, imagine that it requires 2% more effort to drive at 55 mph than it does 45 mph, yet it takes 7% more effort to drive at 60 mph than 55 mph; however arbitrary, this is an example of an exponential curve.
55 is not the magic number for everyone, but through trial and error you can very easily find your vehicles "sweet spot". We've found that long trips obtain the best fuel economy right around 2,000 rpm. Any lower and the engine seems to lug more and greater throttle input is required to keep the vehicle moving. Above 2,000 rpm, vehicle speed and therefore drag force reaches a critical point and, combined with the higher engine speed, fuel economy begins to suffer. There's always a point of diminishing return and each drivetrain combination reacts differently to vehicle speed.
Look into aftermarket upgrades - In our aftermarket air intake testing alone, we were able to measure a 2 mpg increase at highway speeds and a 1 to 2 mpg increase in city driving (largely dependent on traffic conditions). Likewise, converting to an aftermarket exhaust system added another mpg on the highway, and after a thorough tuneup our little 4.6L test mule was seeing as high as 21 mpg at 65 mph (our configuration was rated from the factory at 18 mpg). Be cautious not to fall for false claims or products that obviously produce negligible results. Notable examples include throttle body spacers, which we find make a great paper weight.
Leave the tailgate on and up - Taking the tailgate off or driving with the tailgate down greatly changes the aerodynamic characteristics of your vehicle and has been proven repeatably not to provide noticeable increases in fuel economy. In fact, it may negatively impact fuel economy. The bed of your pickup contains a giant pocket of air that acts like a tonneau cover while you are driving. Air flows over the top of the bubble, and therefore the tailgate does not act like the parachute you've been convinced it is. Lowering the tailgate or removing it will eliminate this pocket of air and addition drag will be placed on the rear of the vehicle, possibly leading to negative results. If tailgate position was a considerable factory in fuel economy, automakers would be using this to their advantage during their own fuel economy tests and it would be outlined in every pickup's owners manual.
Follow the OEM fuel recommendations - Unless the manufacturer suggests or requires premium fuel, stick with regular unleaded. Using high octane fuel in a vehicle that is rated for regular 87 octane will produce negative, if any results. Unless the OEM suggests a high octane fuel, stick to regular. As octane rating increases, the energy content per unit of fuel decreases.