This year Americans have bought more gas than they have in nearly nine years. Lower gas prices have been a gift to drivers and they’ve responded by hitting the road.

Though overall fuel efficiency has improved, people are clearly driving more and may be getting complacent when filling up their tanks. The price of gas can always go back up. Last month Yahoo Finance published a list of mistakes people make when buying gas, and we decided to expand on the list to include some more bad habits that drivers may not be aware can cost them money – mostly in terms of fuel efficiency.

Your tires are underinflated

Underinflated tires increase tire wear and reduce your fuel economy. Tire pressure is determined by the psi (pounds per square inch) in the car tires, and according to the Department of Energy, you can improve your gas mileage by 0.6% on average—up to 3% in some cases—by keeping your tires inflated to the proper pressure.

Discovery Channel’s “MythBusters” tested this rule out by letting the air out of a set of car tires to see if it would have a real effect on gas mileage. Cruising with tires that were 15% underinflated, their car guzzled 1.2% more fuel. And with tires 15% too pumped up, the car used 6.2% less fuel – because “there was less surface area of rubber meeting the road.” Though the cost savings of driving with overinflated tires “worked out to only around $76 per year, which is much less than the potential expense of a tire blowout,” according to “MythBusters” (though overinflating is not recommended, as they could be more easily damaged).

You’re carrying around too much junk

Hauling cargo on your roof increases wind resistance and lowers fuel economy, as does extra weight inside the car. The Energy Department recommends drivers avoid keeping unnecessary items in your car, especially heavy ones. An extra 100 pounds could reduce your miles per gallon by about 1%. The reduction is based on the percentage of extra weight relative to the car’s weight and affects smaller vehicles more than larger ones. So if you’ve been riding around with a set of golf clubs or old sports equipment, consider keeping them in the garage.

You’re changing the oil every 3,000 miles

It’s an old rule of thumb; most cars these days can go more than twice that distance before they need an oil change, say the experts at Edmunds.com. “Oil life monitors automatically sense when your next oil change is needed – based on car speed, engine temperature, climate conditions, number of cold starts and other factors – and they’re utilized by 19 of 34 automakers, according to Edmonds. Refer to the manufacturer’s specified maintenance schedule on how often you should change the oil.

The main advocates of the 3,000-mile oil change schedule are, of course, those who would profit by it: repair shops and service departments at some new-car dealers, says Cars.com, a car research and listings site.

You’re an aggressive driver

You might be an aggressive driver if your cruising speeds range around 75 to 85 miles an hour, you’re constantly accelerating and changing lanes, and you’re often braking sharply. If you decided to calm down and drive with the cruise control, says Aaron Lewis of Edmunds.com, your fuel economy would improve.

“Cruise control is much better than a person at maintaining constant throttle input and speed, which is critical to getting the best possible fuel mileage,” says Toby Schultz of YourMechanic.com.

You really believe the claim of “lifetime fluids”

There is no such thing as a fluid that lasts “a lifetime,” says Schultz, adding that by the time the fluid completely fails and the irreversible damage is noticed, the warranty is expired. Most of these lifetime fluids are based on the idea of lasting about 100,000 miles. After that, the manufacturer doesn’t really care what happens to the car. (Most manufacturers suggest 30,000 to 60,000 miles as the point at which you should change the transmission fluid in a manual transmission, according to YourMechanic.com).

Serious damage can occur to multiple components if a car’s lifetime transmission fluid is left unchanged – including to the filter, oil pan, seals, etc.

Read more: Mistakes you’re making when buying gas