Why is my Subaru Outback using so much gas?
Short answer: In many cases, higher fuel use is due to a mix of driving conditions and routine maintenance. A few targeted checks and small adjustments can often restore normal mpg without major repairs.
More detail: The Outback’s fuel economy is influenced by weather, trip length, weight, and how well the vehicle is maintained. All-wheel drive, aero drag from roof racks, tire condition, and engine or exhaust system health can push actual miles-per-gallon below EPA estimates. Understanding these factors helps distinguish normal variation from a deeper issue and guides practical steps to improve efficiency.
Common causes of higher fuel consumption
Below are the most common reasons Outbacks use more fuel than expected.
- Underinflated or uneven tires, which increase rolling resistance and drag
- Aerodynamic drag from roof racks, cargo boxes, or heavy roof loads
- All-wheel drive being engaged more often or permanently, plus extra weight from AWD components
- Cold weather and short trips that prevent the engine from reaching optimal operating temperature
- Aggressive driving, frequent hard acceleration, or high-speed driving
- Excess weight from passengers, gear, or aftermarket accessories
- Fuel system problems or emissions components (for example, a failing oxygen sensor or restricted catalytic converter)
- Fuel quality and octane level, or a loose or faulty gas cap that allows vapor loss
Addressing these factors can yield noticeable gains in efficiency. For example, proper tire inflation and removing unnecessary roof cargo can save a few mpg in typical real-world driving.
Diagnose and fix: a practical checklist
To pinpoint and correct the underlying causes of high fuel consumption, work through this practical diagnostic list.
- Check tire pressure and tread: Inflate tires to the vehicle manufacturer’s recommended psi and inspect for uneven wear or damage.
- Limit aero drag: Remove roof racks or cargo boxes when not in use; reduce weight on the roof and cargo area.
- Monitor the engine and transmission: If you notice poor acceleration, rough idle, or transmission slippage, consider a professional check for spark plugs, ignition coils, and CVT fluid condition (or transmission service interval).
- Scan for codes if the Check Engine Light is on: Use an OBD-II scanner to check for misfire, lean/rich fuel mixtures, or sensor failures (e.g., O2 sensor, MAF sensor).
- Inspect the air intake and fuel system: Replace a dirty air filter; clean or replace a faulty MAF sensor; consider fuel injector cleaner as a temporary aid if recommended by a technician.
- Check the EVAP and gas cap: Ensure the gas cap seals properly; test the EVAP purge valve and related hoses for leaks or sticking components.
- Look for vacuum leaks and hose damage: A hissing sound or deteriorated vacuum hoses can cause excessive fuel use and rough running.
- Assess engine oil and maintenance: Use the correct grade of oil for your climate and mileage; replace worn spark plugs and ignition components at the recommended intervals.
- Evaluate the exhaust and catalytic system: If the catalytic converter is partially clogged, it can reduce efficiency and power; this requires professional diagnosis.
- Test and adjust driving behavior: Use steady speeds on highways, coast when appropriate, and avoid unnecessary rapid starts to improve mpg over time.
- Track fuel economy over several fill-ups: Keep a log of miles driven and gallons used to see whether mpg improves after maintenance or changes.
If the vehicle continues to show high fuel consumption after these checks, or you notice persistent performance problems, schedule a visit with a qualified Subaru technician. They can perform a deeper diagnostic scan and inspect components that are harder to service at home.
Summary
Most spikes in fuel usage on a Subaru Outback come from a combination of weather, driving habits, and maintenance gaps. Start with simple, non-invasive checks—tire pressure, roof cargo removal, air filter, and a basic code scan—and then address any identified issues. Keeping a fuel-economy log helps you see progress over time. If concerns persist, a professional inspection can uncover less obvious causes such as sensor failures or emissions-system restrictions.
