Saving Money on Gas This Summer (No Matter What's Happening)

It’s been at least a couple of years since we last took a close look at gas mileage and what actually affects it for the average driver. Under normal circumstances, that might not matter much. But these days aren’t normal circumstances.

Between ongoing instability in the Middle East and the effects rippling through the global oil supply, oil and fuel prices have already climbed—and there’s a very real possibility they could go higher as we move into the summer driving season.

Seems like a good time for a refresher.

Because while none of us can control what happens in global energy markets, we can control how efficiently our vehicles use the fuel we’re putting into them. And when gas (and diesel) prices are up, even small improvements in fuel economy start to matter more than they normally would.

So what actually makes a difference? And what doesn’t? Let’s walk through it.

What Really Affects Gas Mileage

Gas mileage isn’t determined by just one thing. It’s the result of how your vehicle is driven, how well it’s maintained, and the conditions it’s operating in. Though they don't all play completelt equal roles.

That’s important, because it means there isn’t a single fix that suddenly improves fuel economy across the board. Instead, it’s about stacking small advantages—each one contributing a little bit to your bottom line.

When you put those together, the impact can be meaningful.

Driving Habits Matter More Than Most People Think

The biggest factor in fuel economy isn’t under the hood. It’s behind the wheel.

Driving habits alone can account for the most noticeable difference in fuel economy. The U.S. Department of Energy has estimated that aggressive driving—rapid acceleration, hard braking, and frequent speed changes—can reduce gas mileage by anywhere from about 15% to as much as 30% on the highway, and even more in stop-and-go traffic. That’s not nothing.

On the other end of the spectrum, you don’t have to become a “hypermiler”—someone who takes fuel-saving to the extreme—to see benefits. Most drivers can pick up meaningful gains just by being more intentional about how they drive.

The goal isn’t to accelerate as slowly as possible. It’s to find the balance. Getting up to speed reasonably efficiently is fine—but flooring the accelerator to get there as quickly as possible burns far more fuel than necessary. What matters most is what happens after that. Once the vehicle reaches cruising speed, maintaining that speed becomes the key to efficiency.

Every time you accelerate, you’re using fuel to build speed. If you then immediately slow down—whether from traffic, poor anticipation, or inconsistent driving—you’re essentially throwing that energy away and having to spend fuel to build it back again. Smoother driving helps preserve that momentum, which reduces how often the engine has to work hard to regain speed.

The level of speed itself that you're maintaining is one of the biggest factors. For most vehicles, optimal fuel efficiency on the highway occurs somewhere between about 50 and 65 miles per hour. Once you go above that range, aerodynamic drag increases rapidly, and fuel economy starts to drop off.

A commonly cited rule of thumb is that for every 5 miles per hour you drive over 65, fuel economy decreases by roughly 5% to 10%. That adds up quickly. For example, if your vehicle averages around 30 miles per gallon at 65 mph, increasing your speed to 75 mph could drop that to somewhere around 27 mpg or lower.

On an eight-hour highway trip, that difference becomes more noticeable than most people expect. At 65 mph, you’d travel about 520 miles and use roughly 17 gallons of fuel. At 75 mph, you’d cover more distance in the same time, but your reduced fuel economy could push your fuel usage closer to 19 gallons. At $3.50 per gallon, that’s an extra $7 or more for the same trip—just from speed alone. Over a full summer of driving, those differences compound.

Then there’s idling, which becomes more common in the summer. Running the engine while sitting still—whether in traffic or parked with the air conditioning on—uses more fuel than people realize. Most vehicles burn roughly 0.2 to 0.5 gallons of fuel per hour while idling, depending on engine size and load. That may not seem like much, but extended idling can quietly chip away at fuel economy over time.

Finally, there’s the question of windows versus air conditioning. At lower speeds—generally below about 30 to 40 miles per hour—driving with the windows down has little impact on efficiency and can be a reasonable alternative to running the AC. But at highway speeds, open windows disrupt the vehicle’s aerodynamics and increase drag, which can reduce fuel economy more than using the air conditioning would. At that point, keeping the windows up and using the AC is often the more efficient choice.

Basic Maintenance Still Makes a Difference

It’s easy to overlook the basics, especially when a vehicle seems to be running fine. But small maintenance items can have a measurable impact on fuel economy—especially when they’re slightly off over long periods of time.

Tire pressure is one of the simplest and most important. Underinflated tires increase rolling resistance, which means the engine has to work harder to move the vehicle. The U.S. Department of Energy estimates that for every 1 PSI drop in average tire pressure across all four tires, gas mileage can decrease by roughly 0.2%. That may sound small, but if your tires are 5 to 10 PSI below the recommended level—which isn’t uncommon—that can translate to a 1% to 2% loss in fuel economy.

On the flip side, slightly higher tire pressure can reduce rolling resistance and improve efficiency. Some drivers will inflate their tires a few PSI above the manufacturer’s recommended setting to capture a small gain in fuel economy. And in controlled conditions, that can result in a modest improvement—typically in the range of 1% or so.

However, there’s a trade-off. Higher tire pressure can lead to a firmer ride, reduced traction (especially in wet conditions), and more uneven tire wear if taken too far. That’s why the safest and most practical recommendation is to stay at or near the manufacturer’s recommended PSI, which is designed to balance efficiency, safety, and tire longevity. Going significantly above that may provide diminishing returns while increasing risk.

Air filters are another commonly overlooked factor. In older vehicles, a clogged air filter could noticeably reduce fuel economy because it restricted airflow to the engine, directly affecting combustion. In modern vehicles, engine control systems can compensate to a large extent, so the impact on fuel economy is typically smaller. That said, a severely restricted air filter can still reduce efficiency under certain conditions, particularly during acceleration or higher engine loads.

In practical terms, replacing a very dirty air filter in a modern vehicle might improve fuel economy by a small margin—often in the range of 2% to 6% in more extreme cases, though usually less. More importantly, it helps restore proper engine performance and ensures the system is operating as intended.

Spark plugs, fuel injectors, and other components involved in combustion don’t usually fail all at once. Instead, they gradually become less efficient over time. That loss of efficiency doesn’t always show up as a noticeable problem, but it can still affect fuel economy. Keeping those systems in good condition helps maintain the level of performance and efficiency the engine was designed to deliver.

Summer Conditions Work Against You

Summer driving introduces a few additional challenges that people don’t always think about.

Heat affects fuel in subtle ways. Gasoline is more volatile at higher temperatures, which can contribute to evaporative losses and slightly reduced energy density. You won’t notice this directly, but it’s part of the overall picture.

Air conditioning is the more obvious factor. Running the AC puts an additional load on the engine, especially in stop-and-go driving. That doesn’t mean you shouldn’t use it, but it does mean there’s a tradeoff between comfort and efficiency.

Then there’s weight and aerodynamics. Summer often means road trips, luggage, coolers, and sometimes roof racks or cargo carriers. Extra weight requires more energy to move, and anything that disrupts airflow—like a roof rack—can increase drag and reduce fuel economy, particularly at highway speeds.

Does It Matter When You Fill Up?

You may have heard the idea that you get more gas if you fill up in the morning, when it’s cooler outside.

The reasoning sounds logical. Cooler gasoline is denser, so in theory, you’d get more fuel per gallon than you would in the heat of the day.

In practice, this doesn’t make much difference.

Gasoline is stored in underground tanks at gas stations, where temperatures remain relatively stable throughout the day. While there can be slight variations, they’re usually not significant enough to meaningfully affect how much energy you’re getting per gallon.

Fuel is also sold by volume, not weight, and modern systems are designed with temperature variation in mind.

So while it’s not harmful to fill up in the morning, it’s not a strategy that’s going to noticeably improve your gas mileage.

Where Fuel Quality and Cleanliness Come Into Play

One area that often gets overlooked is the condition of the fuel system itself.

Over time, deposits can form in fuel injectors and other components. These deposits can affect how fuel is delivered into the engine, including the spray pattern and atomization. When that process isn’t as efficient as it should be, combustion can become slightly less efficient as well.

Modern fuels do contain detergents designed to help keep systems clean, but they’re not perfect. Driving conditions, fuel quality, and vehicle age all play a role in how deposits develop.

Keeping the fuel system clean isn’t about dramatic improvements. It’s about maintaining the level of performance and efficiency the engine was designed to deliver.

Small Improvements Add Up

There’s no single change that will suddenly transform your fuel economy.

But that’s not really the point.

What matters is the combination of small, practical steps. Driving a little more smoothly. Keeping tires properly inflated. Being aware of speed and idle time. Avoiding unnecessary weight and drag. Paying attention to how the vehicle is running over time.

Each of those may only improve fuel economy by a small amount on its own. But together, they can make a noticeable difference—especially when fuel prices are high.

And that’s where we are right now.

With uncertainty in global energy markets and the potential for continued price increases, getting the most out of every gallon matters more than it did a year or two ago.

You may not be able to control the price at the pump. But you can control how efficiently you use what you put in the tank.

And over the course of a summer, that can add up in ways that are hard to ignore.