 copy.jpg)
It’s one thing when gas prices go up—it’s another when your fuel gauge seems to drop twice as fast as it used to. If you’re filling up more often and can’t figure out why, you’re not imagining things. When your car starts burning through fuel faster than usual, it's a sign that something isn’t working quite right.
While it’s normal for fuel economy to vary slightly depending on your driving habits or the weather, a noticeable drop in MPG almost always has a cause. And if it’s left unchecked, it can affect more than just your wallet—it can also lead to reduced performance and long-term wear on your engine.
Driving Habits
Before looking under the hood, it’s worth thinking about whether your routine has changed. Are you making more short trips? Driving in heavy traffic more often? Accelerating harder than usual?
Cold starts and stop-and-go traffic force your engine to work harder, using more fuel in the process. If you’ve been using the remote starter often or idling longer during winter warmups, that can also affect your MPG more than you'd expect.
While habits like these don’t usually cause dramatic drops on their own, they can amplify small problems that are already affecting fuel efficiency.
Tire Pressure and Rolling Resistance
One of the most overlooked causes of poor fuel economy is underinflated tires. When your tires aren’t properly inflated, your engine has to work harder to move the car, which increases rolling resistance and burns more gas.
Even a small drop in pressure—say, five or six PSI—can lead to a measurable drop in mileage. Changes in temperature can make a difference too, especially in areas like Issaquah, WA, where cold mornings and wet roads are common.
Keeping your tires properly inflated and aligned doesn’t just save gas—it also extends the life of your tires and improves handling.
Sensor Issues and Fuel Delivery Problems
Modern cars rely on a network of sensors to control fuel injection and air-fuel mixture. If one of these sensors fails—like the oxygen sensor, mass airflow sensor, or coolant temperature sensor—your engine may burn more fuel than necessary to compensate.
A failing oxygen sensor, for example, can cause your car to run rich (too much fuel, not enough air), which reduces MPG and increases emissions. Often, you won’t even notice a performance issue right away—but your fuel economy will take the hit.
In some cases, a dirty or failing fuel injector might not spray fuel evenly, leading to inefficient combustion and poor mileage.
Air Filters, Spark Plugs, and Routine Maintenance
A dirty air filter can restrict airflow to your engine, which affects how efficiently it burns fuel. In older cars, this used to have a big impact on gas mileage. Newer vehicles adjust automatically, but a clogged filter still reduces performance and fuel efficiency over time.
Old spark plugs are another common culprit. When they start to wear out, the combustion process becomes less efficient, which causes the engine to work harder and consume more fuel.
If your last tune-up was a long time ago, there’s a good chance your car just isn’t running as efficiently as it should be. Routine maintenance might not seem urgent, but it has a big impact on long-term fuel use.
Leaks or Evaporative Emissions Issues
If your fuel economy has dropped sharply and you’ve ruled out obvious causes, it’s worth checking for a fuel system leak or a problem with the evaporative emissions system (EVAP).
Small leaks in the fuel line or gas tank are rare but dangerous. The EVAP system, which prevents fuel vapors from escaping, can also cause a check engine light or gas smell if something’s wrong.
Even if there’s no visible leak, a malfunctioning EVAP component can allow vapors to escape, effectively reducing the amount of usable fuel in your tank.
Don’t Let Poor MPG Become Your New Normal
It’s easy to get used to filling up more often, but don’t make the mistake of assuming your car is just “getting old” and that fuel efficiency is supposed to drop. While mileage might decrease slightly with age, sudden or significant changes are never normal.
The good news is that most causes of poor fuel economy can be fixed quickly—and in many cases, affordably—before they lead to more serious repairs.
Noticing your MPG dropping faster than it should? Let us at Autoworks Of Issaquah in Issaquah, WA, inspect your vehicle and pinpoint the cause. Whether it’s a sensor issue, a fuel system problem, or just overdue maintenance, we’ll help restore your fuel economy and your confidence.