Why Is My Car Getting Worse Gas Mileage?
You know your vehicle.
You know roughly how often you normally stop for gas, how far you can usually travel on a tank, and what kind of fuel economy you tend to see on the dashboard.
So when those numbers suddenly start moving in the wrong direction, it's noticeable.
Maybe you're filling up more often.
Maybe your average MPG has dropped from 28 to 23.
Or maybe you're wondering why your vehicle doesn't seem to get the same gas mileage it did a year ago.
A drop in fuel economy doesn't always mean there's something seriously wrong with your vehicle. Weather, driving habits, tire pressure, traffic, maintenance, and even the type of trips you take can all affect how efficiently your vehicle uses fuel.
But a significant or unexplained decrease can also be a reason to take a closer look.
If you're driving around Fort Wayne and wondering why your car is suddenly using more gas, here are some of the most common factors to consider.
First, What Does MPG Actually Mean?
MPG stands for miles per gallon.
It's a measurement of how many miles a vehicle can travel using one gallon of fuel.
If your vehicle averages 30 MPG, that means it travels approximately 30 miles for every gallon of fuel consumed under those particular driving conditions.
The important phrase is under those particular driving conditions.
Your MPG isn't a fixed number that never changes.
The EPA fuel-economy rating associated with a vehicle is based on standardized testing. Your actual fuel economy can vary depending on how, where, and when you drive.
That's why two people driving identical vehicles can see different MPG.
1. Your Tire Pressure Is Too Low
Tires are one of the first things worth checking when fuel economy begins dropping.
Underinflated tires create additional rolling resistance.
In simple terms, the engine has to work harder to move the vehicle down the road.
The U.S. Department of Energy notes that properly inflated tires can improve gas mileage compared with driving on significantly underinflated tires.
Tire pressure also changes with temperature.
That's especially relevant for Indiana drivers during fall.
As temperatures drop, tire pressure tends to decrease.
You may notice this during the first major cold snap when your Tire Pressure Monitoring System, or TPMS, suddenly illuminates.
Check your tire pressure regularly and use the pressure recommended by the vehicle manufacturer.
You'll typically find that information on a label inside the driver's door area.
Don't use the maximum pressure printed on the tire sidewall as your normal inflation target.
2. Your Driving Habits Have Changed
Sometimes the vehicle isn't the reason fuel economy has changed.
The driver is.
Aggressive acceleration and braking can increase fuel consumption.
If you're regularly accelerating hard from stoplights, speeding up only to brake again, or driving at higher highway speeds, your MPG may decrease.
Think about whether your routine has changed recently.
Maybe you're running late more often.
Maybe you've started driving a different route.
Maybe your commute now includes more traffic.
Maybe you're spending more time on the interstate at higher speeds.
Small changes in driving behavior can add up over an entire tank of fuel.
3. You're Spending More Time in Stop-and-Go Traffic
City driving and highway driving place very different demands on a vehicle.
When you're cruising steadily on the highway, the engine can operate relatively efficiently.
Stop-and-go traffic involves repeated:
Acceleration
Braking
Idling
Low-speed driving
Every time you accelerate the vehicle, the engine needs energy to get thousands of pounds moving again.
That's one reason city fuel economy is often lower than highway fuel economy.
If construction, school traffic, or a new commute has you spending significantly more time stopping and starting around Fort Wayne, your average MPG may decrease even though nothing is wrong with the vehicle.
4. You're Taking More Short Trips
Short trips can be surprisingly inefficient.
Your engine and other components are designed to operate within certain temperature ranges.
When you start a cold engine and drive only a short distance, the vehicle may spend much of the trip warming up.
If your normal routine consists of repeatedly driving two or three miles, shutting the vehicle off, and starting it again later, you may see lower fuel economy than someone driving the same total mileage in one longer trip.
This can become even more noticeable in cold weather.
5. Cold Weather Can Lower Fuel Economy
If you've ever noticed your MPG falling during an Indiana winter, you aren't imagining it.
Cold weather can reduce fuel economy for several reasons.
The engine takes longer to reach normal operating temperature.
Tire pressure can fall.
Cold air creates more aerodynamic drag.
Winter gasoline formulations can differ.
Heaters, defrosters, heated seats, and other accessories may be used more frequently.
Snow and slush can increase resistance.
Drivers may also spend more time idling while clearing windows or waiting for the cabin to warm.
For hybrid and electric vehicles, cold temperatures can affect efficiency in additional ways.
So if your MPG begins falling as temperatures drop, weather may be part of the explanation.
6. You're Idling More Than You Realize
When your vehicle is idling, you're burning fuel while traveling zero miles.
That doesn't help your miles-per-gallon average.
A few minutes here and there might not seem significant.
But consider how often you:
Wait in a parking lot with the engine running.
Sit in a drive-thru.
Warm the vehicle for an extended period.
Wait outside school or work.
Leave the engine running while someone goes inside a store.
Over time, that fuel consumption adds up.
Modern vehicles generally don't need extremely long warm-up periods before normal driving.
Follow your manufacturer's recommendations, particularly during very cold conditions.
7. You're Carrying More Weight
It takes energy to move weight.
If you've recently loaded your vehicle with tools, equipment, boxes, sports gear, or other heavy cargo and left it there, you're asking the engine to move additional mass every time you accelerate.
The difference may be relatively small depending on the amount of weight, but unnecessary cargo can contribute to increased fuel consumption.
This is particularly relevant for trucks and SUVs that may accumulate heavy equipment in the cargo area or bed.
If you don't need it every day, consider taking unnecessary heavy items out.
8. You're Using a Roof Rack or Cargo Carrier
Weight isn't the only issue.
Aerodynamics matter too.
A roof-mounted cargo box, bicycle rack, luggage, or other exterior accessory can increase aerodynamic drag.
That means the vehicle has to use more energy to push through the air, particularly at highway speeds.
If you've recently installed a rooftop carrier and noticed your highway MPG decrease, the two may be related.
Remove unnecessary exterior cargo accessories when they aren't being used if the manufacturer recommends doing so.
9. Your Air Filter May Need Attention
Your engine requires air for combustion.
The engine air filter helps prevent dirt and debris from entering with that air.
Over time, the filter becomes dirty and eventually requires replacement according to the vehicle manufacturer's maintenance recommendations.
On modern fuel-injected gasoline vehicles, a dirty air filter doesn't necessarily cause the dramatic MPG losses sometimes claimed online because the engine-management system can compensate for restricted airflow to a degree.
However, a severely restricted filter can affect engine performance.
The better reason to replace an air filter is simple:
Follow the manufacturer's maintenance schedule and keep the engine's intake system functioning as designed.
10. Worn Spark Plugs Can Affect Engine Performance
Gasoline engines use spark plugs to ignite the air-fuel mixture inside the cylinders.
Spark plugs are wear items.
Their replacement intervals vary significantly depending on the engine and plug design.
If spark plugs become worn or begin misfiring, the engine may not operate as efficiently or smoothly as it should.
Possible symptoms can include:
Rough running
Hesitation
Difficulty starting
Reduced performance
Check-engine light
Increased fuel consumption
Don't replace spark plugs simply because your MPG dropped by one mile per gallon.
Check your maintenance schedule and investigate other symptoms.
11. A Check-Engine Light Can Be Related to Fuel Economy
The check-engine light can illuminate for many different reasons.
Some of them can affect fuel economy.
Your vehicle uses sensors and computers to manage combustion, emissions, fuel delivery, ignition timing, and other functions.
If the system detects a problem, it may store a diagnostic trouble code and illuminate the check-engine light.
Possible problems can involve components related to:
Oxygen sensors
Fuel delivery
Ignition
Airflow measurement
Emissions systems
Other engine-management systems
If your check-engine light is on and your fuel economy has suddenly decreased, don't ignore it.
Have the vehicle properly diagnosed rather than simply replacing whichever part appears in an internet search.
12. Oxygen Sensor Problems Can Affect Fuel Use
Oxygen sensors monitor oxygen levels in the exhaust and provide information the engine-management system can use when controlling the air-fuel mixture.
If an oxygen sensor fails or provides inaccurate information, it can potentially affect engine operation and fuel economy.
A failing oxygen sensor may also trigger a check-engine light.
However, you shouldn't assume an oxygen sensor is bad simply because your MPG decreased.
Modern engine-management systems are complicated.
A diagnostic trouble code can provide direction, but proper diagnosis is still important.
13. Fuel Injector Problems Can Affect Efficiency
Fuel injectors deliver fuel into the engine.
They need to provide the appropriate amount of fuel under different operating conditions.
Problems such as malfunctioning or leaking injectors can affect engine performance and fuel consumption.
Symptoms may include:
Rough idle
Misfires
Poor acceleration
Fuel odor
Check-engine light
Reduced fuel economy
Injector problems aren't the most likely explanation for every MPG fluctuation.
But when poor fuel economy appears alongside drivability problems, the fuel system may need inspection.
14. Your Brakes Could Be Dragging
Your brakes are supposed to slow the vehicle when you press the pedal.
They're not supposed to remain partially applied while you're cruising down the road.
A sticking brake caliper or another brake-system problem can create additional resistance.
The engine then has to work harder to move the vehicle.
Depending on the severity, you might notice:
Reduced fuel economy
Vehicle pulling
Unusual heat from a wheel area
Burning smell
Changes in acceleration
Abnormal brake wear
Brake problems are safety issues.
If you suspect something is wrong, have the vehicle inspected promptly.
15. Wheel Alignment Can Play a Role
Proper wheel alignment helps your tires roll in the intended direction.
If the alignment is significantly incorrect, tires can experience increased resistance and uneven wear.
You may notice:
Vehicle pulling
Crooked steering wheel
Uneven tire wear
Handling changes
Alignment problems are particularly relevant around Fort Wayne because potholes and rough roads can knock suspension and steering geometry out of specification.
If your vehicle suddenly starts pulling after hitting a major pothole, don't ignore it.
16. Your Tires May Be Different
Did your fuel economy change after installing new tires?
That doesn't automatically mean anything is wrong.
Different tires have different:
Tread patterns
Compounds
Weights
Rolling resistance
Sizes
Performance characteristics
An aggressive all-terrain tire, for example, may affect fuel economy differently from a highway-oriented tire.
Changing wheel or tire size can also affect vehicle behavior and potentially the accuracy of certain readings if the new setup isn't within manufacturer specifications.
Choose tires appropriate for your vehicle and driving needs.
17. AWD and 4WD Can Affect Fuel Economy
All-wheel-drive and four-wheel-drive systems provide useful capability, but additional drivetrain components can add weight and mechanical losses compared with simpler two-wheel-drive configurations.
That's why two versions of the same SUV may have different EPA fuel-economy ratings depending on drivetrain.
If you're shopping for your next vehicle, consider whether AWD or 4WD provides enough benefit for your driving to justify potential differences in fuel economy.
For many Indiana drivers, the added traction capability is valuable.
For others, a front-wheel-drive vehicle may meet their needs.
There's no universal right answer.
18. Towing Can Dramatically Reduce MPG
If you've recently started towing a trailer and your MPG dropped significantly, that isn't surprising.
Towing adds weight and often substantially increases aerodynamic drag.
The effect becomes particularly noticeable with large campers and enclosed trailers.
Even a truck that normally delivers respectable highway fuel economy can use considerably more fuel while towing.
Trailer size, weight, shape, speed, wind, terrain, and vehicle configuration all influence the result.
When planning a long towing trip, don't assume you'll travel the same distance between fuel stops as you do without a trailer.
19. Highway Speed Makes a Difference
Aerodynamic drag increases as speed rises.
That means driving faster requires increasingly more energy to push the vehicle through the air.
You may notice that your vehicle gets better fuel economy cruising at moderate highway speeds than it does during long stretches at significantly higher speeds.
This is especially noticeable with larger vehicles such as:
Trucks
Full-size SUVs
Vans
Vehicles towing trailers
Their larger frontal area means aerodynamic drag can have a substantial effect.
20. Your Fuel Economy Display Isn't Perfect
Many modern vehicles display estimated average fuel economy on the dashboard.
It's useful, but it's still an estimate calculated by the vehicle.
If you want to monitor your MPG more closely, you can calculate it manually.
At your next fill-up:
Fill the tank.
Reset your trip odometer.
Drive normally.
At the next fill-up, record how many miles you traveled.
Divide those miles by the number of gallons required to refill the tank.
For example:
You drove 360 miles.
The vehicle required 12 gallons to refill.
360 รท 12 = 30 MPG
Tracking several tanks provides a much more useful picture than judging fuel economy from one short trip.
Don't Judge MPG From One Tank
Fuel economy naturally varies.
One tank might include mostly highway driving.
The next might include:
Traffic
Cold starts
Idling
Short trips
Bad weather
Different routes
More passengers
Cargo
Strong winds
A single disappointing tank doesn't necessarily indicate a mechanical problem.
Look for a consistent trend.
If your vehicle normally averages around 27 MPG and suddenly begins averaging 20 MPG across several tanks without an obvious explanation, that's much more meaningful.
Does Premium Gas Improve Fuel Economy?
Using a higher-octane gasoline than your vehicle requires doesn't automatically produce better fuel economy.
Octane indicates a fuel's resistance to engine knock.
Some engines are designed to require or recommend premium fuel because of their compression ratios, turbocharging, performance tuning, or other factors.
Others are designed for regular gasoline.
Follow the manufacturer's fuel recommendation.
Don't assume that paying more per gallon automatically means you'll travel farther on it.
Does Cheap Gas Cause Bad MPG?
Fuel quality matters, but don't assume every MPG change is caused by the gas station you used.
Gasoline sold in the United States must meet applicable requirements.
There can also be differences in fuel formulations and ethanol content.
If you consistently notice drivability problems after fueling at a particular location, that's worth investigating.
But for ordinary MPG variation, start with the larger factors such as driving conditions, temperature, tire pressure, speed, and maintenance.
What About Ethanol?
Different fuel blends contain different amounts of ethanol.
Ethanol contains less energy per gallon than gasoline, so blends with higher ethanol content can produce lower miles per gallon.
However, you should only use fuels approved for your vehicle.
Most gasoline vehicles are designed to use common E10 gasoline.
E15 is approved for certain vehicles.
E85 is intended for Flex Fuel Vehicles specifically designed to use it.
Check the owner's manual and fuel-filler information before using an unfamiliar fuel.
Can Oil Affect Gas Mileage?
Your engine oil reduces friction, protects components, carries heat, and performs several other important functions.
Manufacturers specify particular oil viscosity grades and performance standards for their engines.
Using the correct oil matters.
Don't simply choose a thicker or thinner oil because someone claims it will improve fuel economy.
Follow the manufacturer's specifications.
And change the oil according to the recommended maintenance schedule or oil-life monitoring system.
How Can You Improve Gas Mileage?
If your vehicle is operating properly, the best improvements often come from relatively simple habits.
Maintain proper tire pressure.
Drive smoothly.
Avoid unnecessary aggressive acceleration.
Reduce excessive idling.
Remove unnecessary heavy cargo.
Remove unused exterior cargo carriers when appropriate.
Keep up with scheduled maintenance.
Use the recommended fuel.
Combine short trips when practical.
Drive at reasonable speeds.
Address warning lights and mechanical problems.
No single trick will transform a large SUV into a tiny economy car.
The goal is to help your vehicle operate as efficiently as it reasonably can.
When Should Worse Gas Mileage Concern You?
Small fluctuations are normal.
A dramatic or persistent decrease deserves more attention.
Consider having the vehicle inspected if poor fuel economy occurs alongside symptoms such as:
Check-engine light
Rough idle
Misfires
Loss of power
Hard starting
Fuel smell
Smoke
Unusual noises
Vehicle pulling
Brake problems
Abnormal tire wear
Those symptoms suggest there may be more happening than a change in weather or driving habits.
Fuel Economy Matters When Shopping for a Used Vehicle
MPG can also be an important consideration when you're looking for your next car, truck, or SUV.
But don't shop based on the MPG number alone.
Consider how you'll actually use the vehicle.
A compact sedan might deliver excellent fuel economy but not provide the passenger space you need.
A large SUV may use more fuel but provide three rows of seating and substantial cargo room.
A truck may sacrifice some efficiency in exchange for towing and hauling capability.
An AWD vehicle may have slightly different fuel-economy ratings from a FWD version while providing additional drivetrain capability.
The best vehicle isn't necessarily the one that uses the least fuel.
It's the one that balances efficiency with the capability, space, comfort, and features you actually need.
Find Your Next Vehicle at Big City Cars
Fuel economy isn't determined by one thing.
It's the result of the vehicle, its condition, its tires, the weather, traffic, speed, maintenance, cargo, and the person behind the wheel.
If your MPG changes, don't immediately assume your vehicle is failing.
Start with the basics.
Check your tires.
Think about how your driving has changed.
Consider the weather.
Review your maintenance schedule.
And pay attention to other symptoms.
At Big City Cars in Fort Wayne, shoppers can compare pre-owned cars, trucks, SUVs, and crossovers with different engines, drivetrains, sizes, and fuel-economy characteristics.
If you're looking for your next vehicle, think about how many miles you drive and where those miles happen.
Someone with a long daily commute may prioritize efficiency differently from someone who needs a truck for towing or an SUV for a growing family.
Understanding what affects MPG can help you take better care of the vehicle you already have and make a more informed decision when it's time for the next one.
