When it comes to what wastes the most fuel in vehicles, there are a few key culprits to be aware of. Getting poor gas mileage can quickly drain your gas tank and your wallet. Understanding what contributes to decreased fuel efficiency is the first step towards improving it.
Aggressive Driving
Aggressive driving behaviors like speeding, rapid acceleration, and hard braking can significantly reduce fuel efficiency. It takes more fuel to power a vehicle at higher speeds compared to lower speeds. Aggressive accelerating and braking also forces the engine to work harder, using extra fuel. Studies have found that aggressive driving can reduce fuel economy by 15% to 30% on highways and 10% to 40% in urban areas.
Why Aggressive Driving Wastes Fuel
There are a few reasons why aggressive driving wastes so much fuel:
- Higher Speeds – Wind resistance increases exponentially with speed. At faster speeds, much more power (and gas) is required to overcome wind resistance.
- Hard Accelerations – When you slam on the gas pedal, it injects more fuel to quickly get the engine revving. This uses fuel that would not be needed with gradual acceleration.
- Hard Braking – Aggressive braking throws away the kinetic energy your car has built up, instead of smoothly coasting to slower speeds.
Estimating Fuel Waste from Aggressive Driving
One estimate found driving 78 mph instead of 55 mph on the highway can reduce fuel economy by 15% to 20%. For a vehicle that normally gets 30 mpg at 55 mph, this would decrease to around 24-25 mpg at 78 mph. Over 10,000 miles per year, that 5-6 mpg decrease would waste 100-200 gallons of gas annually.
Carrying Extra Weight
All the extra weight stored in your vehicle can take a toll on your miles per gallon. A heavy load forces the engine to work harder to accelerate and maintain speed. Estimates indicate that for every extra 100 lbs carried, fuel economy is reduced by 1% to 2%. For a vehicle getting 30 mpg, that’s a decrease of 0.3 to 0.6 mpg for every additional 100 lbs.
Common Sources of Extra Weight
Some common sources of unnecessary weight in vehicles include:
- Extra cargo in the trunk
- Roof racks and carriers
- Packed interior with heavy items
- Too many passengers
- Attached trailer or camper
Fuel Wasted Per Extra 100 lbs
If a 3000 lb car gets 30 mpg normally, an extra 500 lbs could decrease fuel economy by 5-10 mpg. Over 10,000 miles, that’s 50-100 extra gallons burned while carrying the extra weight. Just 200 lbs of excess weight could waste 20-40 gallons over 10,000 miles.
Underinflated Tires
Driving on tires that are underinflated reduces their efficiency and increases rolling resistance. This makes the engine work harder to keep your car moving. Studies have found that every 10 psi drop in tire pressure can decrease fuel economy by 1% to 2%.
Causes of Underinflation
Some common causes of tires being underinflated include:
- Natural air leakage over time
- Temperature changes from seasonal shifts
- Undetected punctures or slow leaks
- Improper tire pressure settings
- Irregular tire pressure checks
Fuel Wasted from Underinflation
For a car getting 30 mpg with a recommended tire pressure of 32 psi, dropping to 22 psi could decrease mpg by 2% to 4%. That’s a reduction of 0.6 to 1.2 mpg. Driving 10,000 miles at this lower pressure would use around 60 to 120 extra gallons of fuel.
Dirty Air Filters
Replacing a clogged, dirty air filter can improve your car’s fuel efficiency by up to 10%. Air filters prevent dirt and debris from entering the engine. Over time, they can become clogged, restricting airflow to the engine. This forces the engine to work harder to draw in air, wasting fuel.
Signs of a Dirty Air Filter
Some signs your air filter needs replacement include:
- Decreased acceleration
- Rough idling
- Reduced power and performance
- Increased exhaust emissions
Fuel Saved from Air Filter Replacement
For a car getting 30 mpg, a clogged air filter could decrease performance by up to 3 mpg. Driving 10,000 miles without replacing a dirty filter could waste up to 100 gallons in additional fuel consumption.
Using the A/C
While air conditioning provides essential comfort and visibility on hot days, it can impact fuel efficiency. Running the A/C compressor and fans requires engine power that directly reduces mpg. Estimates indicate that A/C operation can lower fuel economy by 10% or more under certain conditions.
Factors Impacting A/C Fuel Use
Some factors that influence how much extra fuel is burned by A/C include:
- Vehicle speed – Faster speeds require more A/C power
- Fan settings – Higher fan speeds use more energy
- Temperature setting – Colder settings demand more A/C work
- Outside air temp – Hotter days tax the A/C system more
Fuel Used by A/C
For example, running the A/C in stop-and-go traffic might reduce mpg by 4% to 8%, while cruising on the freeway at high speeds could decrease efficiency by 15% or more. A 10% drop would lower 30 mpg to 27 mpg, wasting 30 gallons over 10,000 miles of driving.
Conclusion
Aggressive driving, extra weight, underinflated tires, dirty air filters, and A/C use can all contribute to wasted fuel. For typical vehicles getting 25 to 30 mpg, these factors can often decrease fuel economy by 10% to 30%. This equates to burning dozens or hundreds of excess gallons per year.
Monitoring driving habits, cargo load, tire pressures, maintenance schedules, and A/C settings can help optimize fuel efficiency. Combining smart driving with proper vehicle care will enable getting every last mile out of each gallon of gas.
Key Takeaways
- Aggressive driving with speeding, rapid acceleration, and hard braking can lower mpg by 15% to 30%.
- Each extra 100 lbs of weight reduces fuel economy by 1% to 2%.
- Underinflated tires can decrease mpg by up to 2% for every 10 psi drop in pressure.
- A dirty air filter can reduce fuel efficiency by up to 10%.
- Using A/C may lower mpg by 4% to 15% depending on conditions.
Comparing Fuel Waste Sources
To visualize the potential fuel waste from each source, here is a comparison table estimating the extra gallons burned over 10,000 miles of driving if mpg drops by 10%:
| Source of Waste | MpG Loss | Extra Gallons Burned |
|---|---|---|
| Aggressive Driving | 3 mpg | 30 |
| 500 lbs Extra Weight | 3 mpg | 30 |
| 20 psi Underinflation | 3 mpg | 30 |
| Dirty Air Filter | 3 mpg | 30 |
| A/C Use | 3 mpg | 30 |
This table demonstrates that all five factors can potentially waste around 30 gallons over 10,000 miles if they decrease mpg by 10%. However, keep in mind that real-world waste amounts will depend on driving conditions and vehicle maintenance specific to each driver.
Recommendations for Improving Fuel Efficiency
Here are some suggested actions you can take to optimize fuel economy from each factor discussed:
Aggressive Driving
- Obey speed limits and avoid rapid acceleration
- Allow plenty distance to vehicles ahead to avoid hard braking
- Use cruise control on highways to maintain steady speeds
Extra Weight
- Remove unnecessary cargo from vehicle interior and trunk
- Avoid overloading passenger seats
- Reduce roof storage when not needed
Tire Inflation
- Check tire pressures at least monthly
- Inflate tires to recommended psi on door placard
- Fix any detected air leaks immediately
Air Filter
- Inspect air filter each oil change and replace if dirty
- Shorten replacement intervals for prolonged dusty driving
A/C Usage
- Park in shade to keep vehicle cooler
- Use recirculated cabin air to reduce A/C workload
- Set fan speeds only as high as needed
- Run A/C only when necessary and turn it off at stops