Why Is My Vehicle Using More Gas?
Fuel economy depends on far more than the engine alone. Tire pressure, vehicle weight, driving speed, traffic conditions, weather, fuel quality, ignition performance, fuel delivery, engine temperature, transmission operation, and even brake condition can affect how many miles your vehicle travels on each gallon.
A small seasonal decrease may be normal, especially during cold weather or frequent short trips. A sudden or continuing decline, however, may indicate an engine-performance problem, sensor failure, fuel-system concern, rolling resistance issue, or overdue maintenance.
Comparing your current fuel economy with your vehicle's normal average can help determine whether the change is significant. Professional testing is especially important when poor mileage occurs with a Check Engine Light, rough idle, hesitation, unusual exhaust smell, or loss of power.
What Else Are You Experiencing?
Select Your Fuel-Economy Symptom
Choose the condition that best matches your vehicle.
Select one of the symptoms above.
What Usually Causes Poor Fuel Economy?
Low Tire Pressure
Underinflated tires increase rolling resistance, forcing the engine to use more fuel to move the vehicle.
Worn Spark Plugs
Worn or fouled spark plugs may cause weak combustion, engine misfires, reduced performance, and increased fuel consumption.
Faulty Oxygen Sensors
Inaccurate oxygen-sensor readings may cause the engine computer to deliver too much fuel.
Dirty or Leaking Fuel Injectors
Deposits may disrupt the fuel spray pattern, while leaking injectors can deliver excessive fuel into one or more cylinders.
Dirty Engine Air Filter
A severely restricted air filter may limit airflow, reduce performance, and affect efficiency on some vehicles.
Engine Misfire
Incomplete combustion wastes fuel and may damage the catalytic converter if the misfire continues.
Thermostat or Temperature Sensor Fault
If the engine remains too cold, the computer may continue using a richer fuel mixture than necessary.
Mass Airflow Sensor Problem
Incorrect airflow readings may cause the computer to calculate the wrong amount of fuel.
Brake Drag
A sticking brake caliper or parking-brake problem creates resistance and forces the engine to work harder.
Wheel Alignment Problems
Incorrect alignment may increase tire scrub, rolling resistance, uneven wear, and fuel consumption.
Transmission Problems
Slipping, delayed shifting, or failure to enter the highest gear may keep engine RPM elevated and reduce fuel economy.
Fuel or EVAP Leak
Fuel leaks, loose fuel caps, purge-valve failures, or other EVAP problems may waste fuel and produce noticeable odors.
Driving Patterns Can Affect Miles Per Gallon
Mostly City Driving
Stop-and-go traffic, extended idling, short trips, and frequent acceleration normally use more fuel than steady highway driving.
Mostly Highway Driving
Excessive speed, low tire pressure, poor alignment, transmission problems, roof-mounted cargo, and aerodynamic drag may reduce highway efficiency.
Cold-Weather Driving
Longer warm-up times, winter fuel blends, tire-pressure changes, heater and defroster use, and short trips can temporarily reduce fuel economy.
Not Every MPG Drop Means Something Is Broken
Seasonal Changes
Cold temperatures, winter fuel, longer warm-up periods, and lower tire pressure may temporarily reduce fuel economy.
Driving Habits
Rapid acceleration, high speeds, extended idling, frequent short trips, and heavy braking increase fuel consumption.
Added Weight or Drag
Heavy cargo, roof racks, trailers, and oversized accessories make the engine work harder.
Mechanical Warning Signs
A sudden MPG decline combined with warning lights, rough running, odors, smoke, hesitation, or brake heat should be diagnosed.