A faulty front oxygen sensor is a very common cause of poor gas mileage.
Gas Mileage FAQ
We often receive questions about fuel economy, so we decided to dedicate a separate page to this topic. If you have more questions, use our contact form, we will post answers on this page.
• My new car is not getting gas mileage that was advertised
• I commute a lot. What's the best way to save on gas?
• Will i get better gas mileage with overdrive On or Off?
• In a pickup truck, do you get better gas mileage with the tailgate down?
• Does K&N filter improve gas mileage?
• Does nitrogen in tires improve gas mileage?
• Common problems that cause poor gas mileage
• How to calculate fuel economy
• How to estimate how many miles you can drive on a tank
• What are some of the most fuel efficient cars
How fast should I accelerate to get better fuel economy?
The answer to this question comes down to a single point: how can you make your transmission shift to the next gear sooner to keep engine rpms low.
With an automatic transmission, if you accelerate quickly, your transmission goes into the sport mode and upshifts at higher rpms. Therefore, gradual acceleration is better for fuel economy because it allows the transmission to upshift sooner.
It's a different story with a manual transmission, as the driver has full control over gear shifting. Some European researches suggest that with a manual transmission, brisk acceleration, followed by a quick shift into the next gear helps improve fuel economy. Of course, "brisk" acceleration doesn't mean "floor it," but rather half to two thirds of the throttle. The point is to upshift to the next gear as soon as possible without straining the engine. I tried this technique on a long trip and was able to get 35.1 mpg (6.7 L/100 km) out of the manual Honda Accord that is rated at 31 mpg (7.6 L/100 km) on the highway. This technique might also work if your automatic transmission has a manual shift mode.
My new car is not getting gas mileage that was advertised
The advertized fuel economy ratings are measured by car manufacturers on pre-production prototypes in a laboratory using standard tests. The EPA reviews the results and confirms about 10-15 percent of them through their own tests.
The real-world numbers will be different depending on driving habits, road conditions, weather, fuel variations, tire pressure and other factors. For example, fuel economy will be worse if you drive mostly through hilly terrain or in cold weather. Therefore, the EPA ratings should be looked at as an average estimate. The EPA says that their fuel economy ratings are more of a tool to compare different vehicles than an accurate number that you will get in your car.
In addition, it's a known fact that a new engine needs to be broken in to perform at its best, so often the gas mileage gets better only after 4,000-5,000 miles.
I commute a lot. What's the best way to save on gas?
If you drive a lot, the best way to save on gas is to look for a more fuel-efficient vehicle (unless you are driving a Prius). Compare fuel cost estimates over a 5-year period of these different models:
|Estimated fuel costs over a 5-year period at 25,000 miles per year (80 percent highway, 20 percent city)|
|2006 Ford F150 4.6L V8, AWD||$25,500|
|2009 GMC Envoy, 4.2L V6, auto, AWD||$22,500|
|2008 Honda Pilot, 3.5L V6, auto, AWD||$21,500|
|2009 Chrysler 300, 3.5L V6, auto, RWD||$17,750|
|2006 Honda CR-V, 2.4L 4-cylinder, auto, AWD||$17,000|
|2008 Honda Accord, 3.5L V6, auto||$15,750|
|2007 Toyota Camry, 2.4L 4-cylinder, auto||$14,500|
|2013 Chevrolet Equinox 2.4L 4-cylinder, auto||$14,000|
|2010 Nissan Altima, 2.5L 4-cylinder, auto||$13,500|
|2007 Honda Civic, 1.8L 4-cylinder, auto||$12,250|
|2013 Chevrolet Cruze Eco, 1.4L-turbo 4-cylinder, auto||$11,500|
|2006 Toyota Prius, 1.5L 4-cylinder hybrid, auto||$8,750|
|2013 Nissan Leaf, electric vehicle||$4,750|
Other things you can do include keeping your tires properly inflated, selecting most fuel-efficient speed and removing extra load.
Will i get better gas mileage with overdrive On or Off?
For better fuel economy, the overdrive should be turned on. Switching the overdrive "off" limits your transmission from shifting into the highest gear, which is the most fuel efficient one.
In a pickup truck, do you get better gas mileage with the tailgate down?
There has been a long debate on this topic. There is a popular belief that if you open the tailgate, there is less resistance to the air flow, but in reality it's not that simple. GM aerodynamic engineer Diane Bloch says a tailgate in the up position is more aerodynamically efficient. This is because with the tailgate closed, air flows over the cab and pushes forward on the rear of the truck. With the tailgate down, the benefits of that airflow are diminished. Bloch also said that “Replacing the tailgate with an aftermarket net is worse than having no tailgate at all.”
The popular Discovery Channel show "Mythbusters" did an experiment and came to the same conclusion: you will get better fuel economy with the tailgate up.
Photos: © General Motors
Does K&N filter improve gas mileage?
The theory behind it is simple: the more resistance for the intake air, the harder the engine has to work to overcome it. In reality, the gas mileage depends on many other factors. A few years back we did an experiment. We filled up our test car, the Mercedes-Benz E320 and drove it for 40 miles and back with an original air filter and calculated the fuel economy. Then we replaced the original filter with the new, pre-oiled K&N filter, filled up again at the same gas station and drove the same route at the same speed. We calculated the fuel economy and found no improvement with the K&N filter; the difference was very small. We got 26.91 mpg (8.74 L/100 km) with the original filter and 26.85 mpg (8.76 L/100 km) with the K&N filter.
Does nitrogen in tires improve gas mileage?
The main benefit of filling tires with nitrogen is that tires lose pressure at a slower rate. According to the EPA, under-inflated tires reduce your gas mileage by 0.3 percent for every 1 psi drop in pressure of all four tires. In 2006, Consumer Reports conducted an experiment and found out that over a 1-year period, tires filled with nitrogen lost an average 2.2 psi from the initial 30 psi, while the air-filled tires lost 3.5 psi. This means that the difference between having air or nitrogen in the tires will be too small to have a notable effect on your fuel economy.
It's also worth mentioning that if you happen to catch a nail or have a leaking valve in one of the tires, that tire will still go flat, whether it is filled with air or nitrogen.
All in all, filling your tires with nitrogen might help a little, but you won't see a huge difference in gas mileage, especially if you check your tire pressure regularly.
How to calculate fuel economy
To calculate fuel economy of your car you need to know two numbers: the distance driven and the amount of fuel used. To get these numbers, follow these steps:
1. Fill-up your car until the first click-off and reset the trip odometer to zero.
3. Next time you need gas, fill up your car again until the first click-off. Write down the amount of fuel it took to fill up (this is the amount you have used since your previous fill-up) and check your trip odometer. To calculate your mpg, divide the distance driven between fill-ups (your odometer reading) by the number of gallons used:
mpg = miles driven / gallons used. For example, it took 14.5 gallons at the second fill-up and your trip odometer reads 460 miles. Your car's fuel economy equals 460 miles / 14.5 gallons = 31.7 mpg. If you drove city and highway, this would be your combined mpg.
To calculate liters per hundred kilometers, multiply the number of liters consumed by 100 and then divide by kilometers driven:
L/100 km = number of Liters × 100 / number of kilometers. For example, you drove 650 kilometers and it took 45 liters to fill your tank at the second fill-up. Your car's fuel consumption is 45 liters × 100 / 650 km = 6.9 L/100 km.
How to estimate how many miles you can drive on a tank
For this, first you need to know your average mpg. To calculate it, you need to estimate, what portion of your trip you will be driving on the highway and what portion will be city driving (stop and go traffic on the highway is still considered city driving).
Let's suppose you are going on an interstate trip where you are going to be driving 70 percent highway and 30 percent city. Let's say that your gets 22 mpg city and 32 mpg highway. Your average mpg for this trip will be:
(0.7 × 32 mpg) + (0.3 × 22 mpg) = 22.4 + 6.6 = 29.0 mpg.
Now you need to look up your tank capacity. You can find it in the owner's manual under 'Specifications'
Let's say your tank capacity is specified at 18.5 gallons. Obviously, you cannot use all 18.5 gallons, you only can use about 90 percent of the tank, until your low fuel warning light comes on. To calculate 90 percent of 18.5 gallons:
18.5 × 0.9 = 16.65 gallons of usable fuel
To calculate how many miles you can drive on a tank you need to multiply amount of usable fuel by your average mpg:
16.65 × 29 = 482.9 miles
This is of course a rough estimation; in reality always expect the number to be lower.
What can cause poor gas mileage
If you noticed a drop in your mpg, it could be a result of a mechanical problem with your car. Common examples include under-inflated tires, a faulty oxygen sensor, old engine and stuck-open thermostat. Scroll to see more common causes:
Common problems that cause poor gas mileage
Bad oxygen sensor
Old engine oil
If engine oil has not been changed in a long time, it becomes thicker and increases friction.
Under-inflated tires increase rolling resistance causing your engine to work harder and burn more fuel.
Lack of tune-ups
With fouled spark plugs like this one your engine will run poorly and inefficiently.
Stretched timing belt
A stretched timing belt or chain will cause lack of power and poor gas mileage.
An engine that is not fully warmed up due to a stuck-open thermostat, will run less efficiently.
Seized brake calipers cause brake drag, resulting in increased rolling resistance and poor fuel economy.
What are some of the most fuel efficient cars?
Nissan Leaf. Photo: Nissan
Nissan Leaf is a simple electric car. It has a battery and an electric motor. There is no exhaust, no fuel tank and no gasoline engine; you never have to pay for gas or do the oil changes. Inside it's a fully functional car with an air conditioner and whatever else you would expect from a modern vehicle. The Leaf seats five and does 0 to 60 mph in a respectable 7 seconds. The only downside is the limited range. Currently the average range is listed at 70 miles on a fully charged battery. This means that if you want to drive from New-York to LA, you would have to find a charging station after every 60 miles or so and charging an electric battery takes time. The range will be shorter in cold weather or when driving in hilly terrain.
Still, the Leaf could work as a daily commuter if you have a second vehicle. You plug it in to charge overnight, commute to and from work, do your groceries and other errands, as long as it's within its range. The EPA estimates, that with 15,000 miles per year, the Leaf will cost you only $500 per year in electricity costs. How can you beat that?
Chevrolet Volt. Photo: © General Motors
Chevrolet Volt is also an electric car, but it has a small gasoline engine that can recharge the battery when it is low. Unlike in hybrid cars, the gasoline engine in the Volt does not power the wheels; it only generates electricity to recharge the battery. The Volt works the same way as the Nissan Leaf: you plug it in overnight to charge the battery and in the morning, it's ready to go. As long as it's within it's battery range, it will run on battery power alone. GM says the Volt can drive up to 38 miles on the battery power.
However, unlike the Leaf, you can easily take the Volt on a long trip. When the battery charge approaches its limit, the gasoline engine kicks in and provides power to recharge the battery. Of course, the Volt is more expensive than the Leaf and uses more complex technology. It's also more upscale inside, although unlike the Leaf, it only seats four.
The annual fuel cost at 15,000 miles per year is estimated at $900.
Toyota Prius. Photo: Toyota
Toyota Prius is the best selling hybrid car. It's powered by a combination of a gasoline engine and an electric motor. The gasoline engine turns on by itself when you accelerate and turns off when you stop. This is the type of car that might feel weird in the beginning, but after a few days of driving, you'd realize "Why I have never though of buying this car before?" It's a roomy practical, well-equipped car. It drives well and is very fuel efficient.
Toyota Prius is proven to be reliable. It holds its value well and is not very expensive to maintain. The EPA rates the 2013 Toyota Prius at 51/48 mpg (4.6/4.9 L/100 km) city/highway. At 15,000 miles per year, the fuel costs are estimated at $1,000. The Prius is an ideal choice if you have long daily commutes. Driving 25,000 miles per year, will cost you only $1,650 annually. To compare, with the same 25,000 miles driven per year, you'd pay $3,550 in gas for the V6-powered Chrysler 300 over the same one-year period.
Mazda CX-5. Photo: Mazda
Mazda CX-5 is one of the most fuel-efficient crossover SUVs. With a small 2.0L direct-injected engine, the CX-5 is still peppy enough for everyday needs. For those looking for more power, the more powerful 2.5L engine is also available. The CX-5's handling is among the best in the segment. The interior quality is pretty good too. The amount of available technology is impressive, although the TomTom-sourced navigation unit is not the best offering on the market. Mechanically, the CX-5 is very simple and should not be expensive to keep. The EPA rates the 2013 2.0L AWD Mazda CX-5 at 25/31 mpg (9.4/7.6 L/100 km) which translates to an annual fuel cost of $1,750 at 15,000 miles per year.
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