Having a fuel-efficient car that doesn’t guzzle gas is important for every driver. Not only does it save you money at the pump, but it reduces your carbon footprint as well. However, there are many factors that can cause your car’s fuel economy to drop, resulting in it burning through gas faster than it should. Here’s an in-depth look at what might be causing your car to be thirstier than normal.
Aggressive Driving
Aggressive driving behaviors like speeding, rapid acceleration, and hard braking can significantly reduce fuel efficiency. Here’s a breakdown of how each impacts MPG:
- Speeding: The faster you drive, the more wind resistance your car faces, increasing fuel consumption. For every 5 mph over 50 mph, fuel economy is reduced by 7% on the highway.
- Rapid acceleration: Accelerating aggressively uses more fuel and puts the engine under strain. It’s best to accelerate gradually and smoothly.
- Hard braking: Aggressively braking wastes the momentum your car has built up and requires more gas to get back up to speed. Smooth, gradual braking is more efficient.
Slowing down, braking earlier and more gently, and accelerating lightly can all help counteract aggressive driving habits that burn extra gas. The table below illustrates the impact speeding has on fuel economy across different vehicle types:
| Vehicle Type | 50 mph | 55 mph | 60 mph | 65 mph |
|---|---|---|---|---|
| Small sedan | 41 mpg | 38 mpg | 35 mpg | 33 mpg |
| Midsize sedan | 35 mpg | 32 mpg | 30 mpg | 28 mpg |
| SUV | 26 mpg | 24 mpg | 22 mpg | 21 mpg |
Low Tire Pressure
Driving on underinflated tires increases rolling resistance, forcing your engine to work harder to move your car. This translates to more fuel being used to maintain speed and acceleration.
The U.S. Department of Energy estimates that every pound per square inch (PSI) your tires are underinflated decreases fuel economy by 0.2%. Even slightly low pressure like 5 PSI under the recommended level can reduce MPG by 1%.
The table below shows how tire pressure impacts the fuel economy of a midsize sedan:
| Tire Pressure | Fuel Economy |
|---|---|
| 35 PSI (5 PSI underinflated) | 28 MPG |
| 30 PSI (10 PSI underinflated) | 27 MPG |
| Recommended 40 PSI | 30 MPG |
Checking and inflating your tires to the recommended pressures at least once a month can improve fuel efficiency and prevent excess gasoline usage.
Dirty Air Filters
Your car’s air filters keep debris and contaminants from entering the engine. But when they become clogged with dirt, dust and other gunk, it restricts air flow to the engine.
This lack of oxygen forces the engine to work harder to draw in air, decreasing combustion efficiency and using more fuel in the process. Replacing a severely dirty air filter can improve gas mileage by up to 10%.
The recommended interval for changing your air filters varies by vehicle make and model, but typically falls between every 12,000 – 30,000 miles. Refer to your owner’s manual or ask your mechanic for the ideal replacement timeline.
Using the A/C
Air conditioning places extra load on your car’s engine to power the A/C compressor, particularly during start-up when the interior air is hot. This added strain can increase fuel consumption when the A/C is running.
It’s estimated that using A/C can reduce fuel economy by 5-25% depending on the vehicle and how high the A/C is running. At lower speeds around town, the impact is less significant at 3-4%. But at highway speeds over 55 mph, that loss can jump to 15-25%.
When possible, use the vent setting instead and open windows to avoid relying on A/C. Regularly replacing dirty cabin air filters can also help your system run more efficiently and may diminish the MPG impact.
Excess Weight
The heavier your car is, the harder the engine must work to accelerate and maintain speed. This results in more fuel being consumed, especially during stop-and-go city driving.
An extra 100 lbs in your car can decrease MPG by up to 2%, while an extra 500 lbs may cut fuel economy by over 10%. Removing unnecessary cargo, heavy accessories, or racks/holders when not in use helps lighten the load and the impact to your gas mileage.
Old Spark Plugs
Over time, the electrodes on spark plugs get worn down and covered in deposits. This makes it harder for them to ignite combustion efficiently, resulting in incomplete burning of fuel.
Replacing worn spark plugs restores optimal combustion and can improve fuel economy by 4%, according to FuelEconomy.gov. The recommended interval for new plugs is typically 30,000 to 100,000 miles depending on your specific car.
Using the Wrong Motor Oil
Using motor oil with the improper viscosity grade for your vehicle can decrease fuel economy. Lighter oils make the engine work harder, while heavier oils create more friction and drag.
Always follow your vehicle manufacturer’s recommendations on motor oil viscosity. For example, most modern cars use 5W-30 or 0W-20 oil. Switching to the wrong viscosity could lower MPG by 1-2%.
Faulty Oxygen Sensors
The oxygen sensors in your vehicle monitor gas levels in the exhaust to tell the engine’s computer how much fuel to inject. When they malfunction or get contaminated, it provides incorrect data to the computer and throws off the air-fuel ratio.
This leads to an imbalance that reduces combustion efficiency and fuel mileage. Replacing defective oxygen sensors can help restore lost MPG and prevent wasted gas.
Drag from Roof Racks
Leaving empty roof racks or carriers on your vehicle when not in use adds unnecessary aerodynamic drag. At highway speeds, this wind resistance makes the engine work harder, using extra fuel.
Improperly mounted racks or ones in disrepair are even worse for drag. Removing racks or crossbars when not needed or replacing damaged ones improves gas mileage. Fairings can also minimize drag from required roof racks.
Low-Quality Gasoline
Not all gasoline is created equal. Using lower-grade fuel with less detergent additives can gunk up fuel injectors and valves over time, reducing combustion efficiency. This leads to wasted fuel from incomplete burning.
Brand and top tier gas stations maintain higher fuel quality standards. When possible, opt for premium gas, especially if your car requires or recommends it for maximum performance and mileage.
Cold Weather Operation
Colder ambient temperatures make your engine work harder, using more gas to warm up and reach optimal operating temperature. This can lower winter fuel economy by 15-30%.
Short trips and frequent cold starts during winter compound the issue further. Limit idling to warm up, combine trips, and use the recommended viscosity oil for cold weather to counteract the impact on MPG.
City vs Highway Driving
Stop-and-go driving in the city with frequent braking and acceleration is inherently less fuel efficient than steady highway cruising. This is due to the constant changes in momentum working against you.
Combining errands into fewer trips and optimizing your route to limit drive time in congested traffic can help limit fuel burned in city driving. But you’ll always use more gas around town versus maintaining speed on the highway.
Conclusion
From aggressive driving to cold weather effects, many variables impact your real world MPG. But being mindful of these factors and making smart maintenance choices like checking tire pressures and changing dirty air filters can keep your car from guzzling extra gas unnecessarily. Focus on the basics of smooth driving, proper care and routine upkeep, and your car’s fuel economy performance will be optimized.
