For some people, car maintenance is easy. They follow the little schedule that comes with the vehicle manual, get their oil changed on time, and rotate their tires every 6,000 to 8,000 miles. Others aren’t quite so mechanically savvy; they know where the gas tank is, but that’s about it (and if they live in New Jersey, they might not even know that).

We’ve got good news for the irresponsible people and bad news for the responsible ones: Regardless of which group you fall into, there’s a pretty good chance you’re messing something up. We looked into a few of the most common chestnuts of car maintenance wisdom—only to find that they’re often misleading or outright wrong.

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To extend your vehicle’s lifespan, optimize handling, and avoid overspending at the pump, keep these following misconceptions—and the actual tips that follow—in mind.

1. “Get the cheapest gasoline you can find. It’s all the same stuff.”

Typically, if you’re looking for gas, you’re looking for the cheapest fuel available. There are dozens of smartphone apps designed to help drivers find inexpensive gasoline, and if you’re on the road and you’ve got the option of paying either $2.56 or $2.53, you’ll make the obvious decision.

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However, gas formulas aren’t identical, and the detergents in some products can actually affect the long-term health of your engine.

The oil industry’s “Top Tier” program is a gasoline performance standard, and it actually seems legitimate. To get the designation, gasoline marketers have to maintain certain detergent levels in their product. The program is at a fairly wide variety of gas stations, from Amoco to Valero (unfortunately, there aren’t any gas stations that start with a Z that are a part of the program).

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In 2016, an independent laboratory hired by the American Automobile Association found that Top Tier gasoline reduced engine deposits substantially. Granted, a motor club’s proprietary report isn’t exactly peer-reviewed research, but the full report (link opens a PDF) notes that Top Tier gasoline isn’t significantly more expensive than alternatives—it averages about three cents more per gallon—and it’s certainly cheaper than a new engine.

2. “For a performance boost, go with premium gas.”

But while you’re pumping up, don’t make the mistake of putting high-octane fuel into a vehicle that doesn’t need it. We know, we know—that big “premium” sticker looks pretty tempting, but the word “premium” is pure marketing.

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According to Kelley Blue Book, high-octane (or “premium”) fuel reduces an engine’s “ping” or “knock”—basically, the fuel/air mixture that powers the pistons can combust before it’s supposed to, creating a pinging or knocking sound—but relatively new engines that aren’t designed to take advantage of the higher octane rating will simply burn off the excess. You’ll have wasted your money, and you won’t notice any extra power.

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With that said, if you have an older vehicle, carbon deposits in the engine might actually make the high-octane fuel worthwhile. That’s because the engine’s octane rating rises over time as the deposits raise the combustion ratio. Essentially, the engine becomes less efficient, and uncontrolled combustion messes with the engine’s balance, causing pinging. By adding premium gas to an older car, you’re counteracting the carbon deposits, so the car will be able to run without pinging like crazy.

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If you’re considering the fuel upgrade, check with your mechanic before making the switch; while premium gas won’t harm a lower-octane engine, it won’t be too kind on your pocketbook, so you’ll want to make sure that you’ll actually benefit from the upgrade. For newer vehicles, simply follow the fueling instructions in the user manual.

3. “Tire maintenance is simple: Check tread depth, then you’re good to go.”

If you’re paying any attention to your tires, good for you. According to one 2012 study, about 13 percent of American automobiles have at least one bald tire, and few events are scarier or more dangerous than a blowout.

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However, tire inflation—or lack thereof—is also a big problem. A National Highway Traffic Safety Administration study of tire inflation pressure showed that 12 percent of all somewhat-aged passenger vehicles (2004–2011 models) in the United States have at least one tire under-inflated by at least 25 percent. That was true even for vehicles with tire pressure monitoring systems, so if you’re waiting for that little light to warn you that it’s time to air up, think again.

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We shouldn’t have to tell you this, but it’s really, really important that you keep your tires properly inflated.

“Properly inflated tires will reduce frictional forces on the tires, thus reducing heat. This will increase the life of the tire,” says Robert Dillman of Dillman Driving School in Florida. “Properly inflated tires also increase the tire contact patch and provide a consistent and stable sidewall in the event your vehicle slides. It reduces the tire’s propensity to roll under the wheel in hard turning or skidding and reduces tire failure or de-beading.”

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Hopefully, you already know the basics. Check the pressure when your tires are cold, never over-inflate, and plan on adding air every month or so as the tires naturally lose pressure. Oh, and if you’ve been using the little sticker on your driver’s side door as a guide, you might want to change your approach.

“Inflate your tires to the recommended PSI found on the sidewall, not on the vehicle sticker,” Dillman says. “Tires are made with different ply materials, heat ratings, and compound densities. Inflating to the vehicle sticker will provide the ride quality initially intended, but inflating to the sidewall max recommendation provides numerous more benefits.”

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We should note that this is a controversial subject, even among driving experts. The Star Tribune‘s Paul Brand noted that filling to the max PSI will improve handling to an extent, but will also reduce fuel efficiency and tire tread life.

While we’re on the subject, a quick car hack: If you’re stuck with a “low tire pressure” warning light and you don’t have a pressure gauge handy, you can touch each of the tires with your hand to find the culprit. Since part of the tire’s job is to reduce friction with the road, an under-inflated tire will be significantly warmer than properly inflated tires.

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Of course, this is only an emergency measure, as it can’t help you determine how much air to add. The best course of action is to buy a cheap tire gauge during your next visit to the gas station and stash it in your glove compartment so you’ve got one when you need it.

4. “To avoid wasting gas, roll down the windows.”

By all means, if you’re cruising at a low speed, roll those windows down and hang your arm out of your yellow 2002 Dodge Neon. How else are you going to impress potential suitors?

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But when you get up to speed, you’ll want to switch over to the AC. That might come as a surprise for those of us who learned in driver’s ed that the AC sucks up more gasoline than a thirsty…uh, gasoline-drinking animal, but modern air conditioners aren’t quite the inefficient horrors of the past.

Using the air conditioner on the highway will consume some fuel, but not much compared to what you’d spend by rolling your windows down. The U.S. Department of Energy recommends running the air conditioner at highway speeds since open windows increase an automobile’s drag significantly, forcing the engine to work harder to maintain speed.

As USA Today noted, there’s another reason to keep the AC on: If you’re comfortable, you’re less likely to make driving mistakes that could lead to an accident.

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Of course, if you’re really worried about fuel efficiency, look to your driving habits. Aggressive drivers can waste up to 40 percent more gas than their calmer contemporaries, according to the EPA. Avoiding road rage—and keeping your attention on your driving—can save you anywhere from $0.28 to $1.13 per gallon, depending on traffic conditions and other factors.

5. “If your battery dies, jump-start your car.”

We don’t really think about our batteries until they stop working, but the best practice is to switch out your battery before it fails to start your car.

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AAA recommends testing your battery regularly once it’s three years old. While some units can last upwards of five years in relatively cool climates, factors like heat, vibration, and usage can cause a battery to fail much earlier, so the best course of action is to test regularly and switch out your battery when it’s showing signs of wear.

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If you do find yourself with a dead battery, try to avoid jump-starting your car unless it’s absolutely necessary. Doing so will create a voltage spike that can damage systems in the donor vehicle, even if you follow the proper process for jump-starting (blogger Rick Muscoplat explains the science behind that risk in detail here). Newer vehicles also have a number of computers which can be easily damaged by sudden surges of electricity.

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A better option is to keep a jump-start pack in your vehicle. You can pick them up for under $100, and that’s much cheaper than hiring a tow truck. Oh, and make sure that your battery is actually bad; clean the terminals with some sparkling water, or if that’s not available, cola. The carbonated liquid should clean off any corrosion, potentially allowing your vehicle to start one time. You’ll still need to figure out why your battery is corroding, but at least you’ll make it to the mechanic.

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