Tips for Increasing Your Vehicle’s Fuel Economy
Fuel costs are on the rise once again. If there’s anything vehicle owners have learned from the last few years, it’s that gas mileage is important. Even when gas prices dip down in the short term, you can always expect them to bounce back up again. And that’s why every driver, on-road or off, can benefit from understanding which driving strategies and vehicle modifications improve gas mileage.
How and where you drive
You can achieve gas mileage improvements of 2 to 4 mpg simply by changing the way you drive. Follow these tips to do it.
- Manage acceleration: You don’t want to accelerate too quickly or too slowly. Find the middle ground. The goal is to get into higher gears as soon as possible, without being too aggressive on the throttle.
- Minimize idling: Keep the idling to a minimum by watching the traffic ahead and timing your momentum. The vehicle burns less fuel accelerating from a dead stop than it does accelerating from a very low speed. If you’re stuck in a traffic jam, turn your engine off.
- Use cruise control: Even at 45 mph, cruise control conserves fuel. If you are traveling a long distance, the cruise control can save you as much as 1 or 2 mpg.
- Shorten your warm-up: Don’t wait extended minutes for your engine to warm. You really only need to wait for the oil pressure to stabilize. Once that happens, you can get moving.
- Get a block heater: If you live in a cold-weather climate, a block heater allows you to shorten your warm-up time significantly.
- Coast: Take advantage of momentum provided by downhill roads and lighten your pressure on the gas pedal.
- Relax: Stress encourages you to drive aggressively, so try to keep your mind relaxed when you’re on the road. Music or talk radio might keep you from thinking about being late. If that doesn’t work, make it a habit to leave early and plan for any potential traffic.
- Shift earlier: Shift early and get into your highest gear quickly.
- Reduce your freeway speed. Your truck or Jeep is not aerodynamic. The faster you go, the more fuel you burn.
- Manage your A/C use: Your A/C uses more fuel at low speeds than it does at high speeds. But, driving with your windows rolled down on the freeway also decreases fuel economy, because your rig has poor aerodynamics. Some tests indicate that during freeway driving, the fuel impact of using the A/C is slightly better than the fuel impact of driving with the windows down.
You can probably incorporate the above tips into your driving relatively easily, but changing where you drive may be more difficult. A stop-and-go commute is terrible for your fuel economy, but you can’t just go and get a new job. You could try alternate routes or a different schedule. If you can drive around the stop-and-go traffic, you might use less fuel, even if you have to cover a greater distance. A more effective solution might be to leave earlier or later to avoid the traffic and benefit from the shortest route.
How tire pressure affects fuel economy
To find out what impact tire pressure has on fuel economy, we did a test on a stock 2005 Ford F-150 with OE General Grabber TR 245-70R16D tires. The test involved driving the truck over a 10-mile course with four different tire pressures. We measured the fuel economy with an Edge Evolution programmer, and mimicked an inexperienced driver. Our test pressures were:
- Maximum pressure of 65 psi
- 50 psi in the front and 60 psi in the rear, as recommended by Ford
- Empty cruising pressure, according to tire load inflation charts
- Underinflated pressure
From the maximum tire pressure to the underinflated level, the difference in fuel economy was ¾ mpg. This was the largest difference measured; the fuel performance was very similar across the maximum level, the Ford-recommended levels, and the empty cruising levels.
Your choice of fuel makes a difference
The gas or diesel you put in the tank does affect fuel efficiency. Differences in BTU (British Thermal Units) content from one brand to another can lower mpg performance by 2-4%. (BTU quantifies the amount of stored energy in fuel.) Fuels with lower BTU tend to be less efficient. Some examples are oxygenated fuels, winter grades of gasoline, and fuel/ethanol blends. In blends, a higher ethanol component can mean lower gas mileage. E85, which is 85% ethanol, can decrease your fuel economy by 15-25%. In a perfect world, the lower cost of the ethanol blend makes up for the poor gas mileage. That often isn’t the case currently, but that could change in the future.
Diesel fuel is less efficient than it used to be, due to government regulations. These regulations pushed through a new formulation with a lower sulphur content. Since that change, some owners have seen a 2% decline in fuel performance. As with gas winter blends, diesel winter blends are less efficient.
Biodiesel is also less efficient that regular gas, due to its lower BTU content. Biodiesels with higher biofuel content have a greater negative impact on fuel performance. You can determine relative biofuel content by the name of the blend; B20, for example, has lower biofuel content than B100. B20 has roughly 2% lower fuel economy relative to gas. For B100, the difference is closer to 10%. As with ethanol blends, this lower fuel economy is supposed to be offset by lower prices. This may start to become reality as the biofuel infrastructure continues to develop.
Vehicle modifications to improve fuel economy
Building your vehicle for off-road performance inevitably reduces your fuel economy. You can’t make up for these losses with bolt-on products, but you can lessen them to some extent. Know that none of the individual upgrades described below will single-handedly create huge gains in fuel performance. Further, the gains you can achieve depend on how your vehicle is currently set up and on the way you drive. We have provided average gains, taken from several different sources. Your experience could be different.
Aerodynamics - Off-road vehicles generally have poor aerodynamics. A suspension lift and massive tires make the front of your rig bigger and bulkier, which means your vehicle does not cut through the air efficiently. Other popular accessories, like bars, bumpers, lights, and racks, worsen the problem. Poor aerodynamics hurt your fuel economy more at higher speeds. If you are just beginning to build up your vehicle, choose a lower lift and smaller tires. Keep the bolt-on pieces on the outside to a minimum. If your vehicle is already built, you’ll have to pay more attention to the way you drive to offset the poor aerodynamics.
You should also remember to remove any gear you don’t need. If you’re just driving to work, for example, unload your off-road equipment and leave it in the garage. A more extreme strategy is to design and build some custom removable pieces that direct airflow away from the truck body. At freeway speeds, you can probably achieve a fuel economy improvement of 3 to 4 mpg.
Camshaft replacement - You can see some benefit by switching out a performance camshaft for a milder model. Stock camshafts are generally pretty fuel-efficient. If you already have a stock version, the cost of replacing it with an economy or RV cam may not be worth the potential gains. You could look into an economy model once your stock cam actually needs to be replaced.
Increased compression ratio - A higher-ratio engine will have better fuel economy than a lower-ratio engine. If you upgrade an engine with an 8:1 ratio to 9:1, you might see an improvement of about 5%. Know that you may have trouble getting an older engine to run ping-free with a ratio higher than 9.5:1.
Other engine upgrades - You can take steps to reduce the internal friction in your engine with roller rockers, roller lifters, and light valve spring pressures. This might produce an improvement of 1% or so. You can improve combustion and volumetric efficiency with exhaust modifications. Some ideas are to increase the size of the exhaust values and to use thermal coatings in the combustion chamber and on the piston crowns. These really aren’t efficient options unless you intend to rebuild the engine anyway.
Exhaust upgrades - Depending on what’s on your vehicle currently, you can sometimes achieve sizeable fuel economy increases by switching out the exhaust. Low-restriction mufflers, cat-back exhaust systems with mandrel bent pipes, and long-tube headers can all be effective. Your gains might range from 1% to 10%. If you have a very inefficient factory manifold, you might also see a nice improvement from installing shorty headers.
Fuel system modifications - Switching out an old carburetor can add a 2% gain, as long as the new carb has a low CFM rating. You can achieve a similar gain by converting your carburetor using a bolt-on EFI kit, depending on the programming of the EFI.
- Programmers - You might get a small increase in fuel economy with a programmer or chip for your gas engine. Be sure to pick a programmer that has custom tuning options. You can play with the shift points and timing to optimize your mpg performance. If you’re driving a diesel, a programmer can optimize your fuel pressure and timing on the lowest level setting.
- Intake manifold - Some aftermarket intake manifolds can deliver fuel economy gains, but others are only designed for gains at high rpms. You should review the specs before you buy, so you know what to expect.
- Cold air intake - Cold air intakes will improve fuel efficiency, only to the extent that they are actually delivering colder air versus your stock intake.
- Air cleaners and filters - Air cleaners and filters generally don’t produce much in the way of fuel economy.
Gearing - If you have stock tires, the OE gearing will be the most fuel-efficient. Things change, though, when you increase your tire size. Gearing changes do impact fuel economy, but there are many factors that come into play. The engine’s torque curve, aerodynamics, and weight are a few examples. The taller tires on your off-road vehicle reduce the engine rpm, no matter how fast you’re traveling. The drawback is that the engine has to do more to accelerate. So you might see increased fuel efficiency while you are cruising on the freeway, and decreased fuel efficiency when you’re starting and stopping on city streets. Low gearing can help, because you then have the ability to speed up without as much throttle.
There is a cruising rpm range where your engine will achieve its maximum fuel economy. This typically happens in the lower third of the engine’s torque plateau — assuming the engine has the torque necessary to handle the load at that speed. If it doesn’t, you end up lugging the engine with the throttle open just to maintain your speed. And, that uses up a lot of fuel. If the engine can hold the increased speed with less throttle, you can get away with a few higher rpms than stock, without hurting your mpg performance.
Ignition upgrades - You might get tiny improvements from making ignition system upgrades. Some examples include hotter coils and ignition modules, performance plug wires, and higher quality spark plugs. Any improvement would be very dependent on what you are replacing. Also, you’re likely to see a greater improvement if your vehicle has a distributor. You can also try modifying your timing advance curve and timing settings. Optimizing these settings could deliver an improvement of up to 5% if you know what you are doing.
Lubricant change For the best mileage, run the lightest oil possible for your climate and conditions. You might also try switching to a slippery, synthetic oil, which will add a variable amount of fuel economy, depending on what’s being replaced.
Electric fan conversion - Installing an electric fan will improve your fuel economy for freeway cruising. The gains can be in the neighborhood of 5-10%. This assumes your new electric fan effectively keeps your engine cool. You’ll see a much lower benefit during city driving.
Tires - Lower rolling resistance and friction means better fuel economy. No matter what type of tires you have, you can reduce the rolling resistance by maintaining maximum tire pressure on the sidewall. The drawback is that your ride quality will deteriorate slightly. Also note that the type of tire impacts your fuel economy too. Highway tires are the most efficient, followed by all-terrains, mudders, and mudders with aggressive tread. The compound plays a roll too. Hard rubber is more efficient, because it generates less friction than soft rubber.
Weight - This was covered briefly above. Keeping your total vehicle weight as low as possible can create a significant increase on your fuel economy. For daily driving, set aside your off-road equipment. If your gear weighs a few hundred pounds, removing it might give you an extra couple of miles per gallon. This assumes you drive a low-powered vehicle. The gains for big truck with a big engine won’t be as noticeable, but they’re likely to add up over time. One study demonstrated a 0.4-mpg improvement for a gas-powered Ford truck when it was empty, compared to the same truck carrying an 850-lb. load.
Measuring your fuel performance
You can calculate your fuel performance by dividing the miles you’ve driven by the number of gallons you’ve used. While this calculation is relatively simple, your result can be inaccurate, depending on where you get your numbers.
Odometer readings - Your odometer might be inaccurate if you’ve made changes to your tires and gear ratio without adjusting your speedometer. So, with bigger tires, the number on your odometer might be lower than it should be. If your calculation is based on fewer miles than you’ve actually driven, your calculated fuel economy will be higher than what you’ve really achieved.
On the other hand, lower gears might result in your odometer showing more miles than actual. In turn, your calculated fuel economy will be worse than actual performance. Of course, gearing and tire changes done simultaneously could cancel each other out. Or not.
The easiest way to test your odometer is to compare your readings to mile markers on the highway. If the odometer reading is off, you can calculate how to adjust for the difference:
- Your correction factor will be the actual miles divided by the miles shown on your odometer. If your odometer reads 1.2 and you’ve only driven one mile, the calculation is 1/1.2, or 0.83.
- Use the correction factor to calculate your actual miles driven. If your odometer indicates you’ve driven 150 miles, then you’ve actually driven 150x.83 miles, or 124.5 miles.
Fill level - Your fuel economy readings are more accurate when your tank is filled to the same level every time. This can be tough in practice. You can reduce the variables at play by using the same pump in the same station for every fill. Or, at least avoid filling the tank when the vehicle is on any type of incline. The pump’s automatic shutoff should be triggered at the same time no matter where you are, but pay attention just in case.
Diesels are more problematic because diesel fuel foams. The amount of foaming varies, depending on how fast you are pumping. Try adding the final gallons very slowly and fill the tank all the way to the top if you can.
Tire size - To identify an appropriate gear ratio following a tire swap, first divide the new tire diameter by the old tire diameter. Multiply that quotient by the vehicle’s original gear ratio. If the result falls between two available options, you have to choose between highway fuel economy and acceleration performance. The lower gear ratio will have better highway fuel economy. The lower ratio will have better acceleration performance, trail performance, and in-town fuel efficiency.
Balancing upgrade cost with potential benefits
You can run a few calculations to help you decide which upgrades are worth the expense. Note that this calculation is not exact, because you have to guess on the potential mpg increase. But, you can play with different numbers to determine where your cost/benefit threshold is.
Start by noting these figures:
- Cost of the upgrade
- Expected mpg increase
- How many miles you drive annually
- Your current mpg
Here are the steps of the calculation:
- Determine your gallons of gas used per year by dividing your miles driven annually by your current mpg.
- Add the expected mpg gain to your current mpg to get the post-upgrade mpg.
- Divide your miles driven annually by the post-upgrade mpg. This tells you how many gallons of gas you’ll use after the upgrade.
- Subtract this number from the number of gallons you’re currently using each year.
- Multiply the result by the current per-gallon price for gas. This is what you’ll save annually, at current gas prices, after the upgrade.
You might choose to go forward with an upgrade if it pays for itself after a year or two of driving. If it takes longer than that to pay off, consider how long you’ll keep the vehicle before you proceed. You will lose money on the deal if you sell the rig before you break even on the upgrades.