There are thousands of mods on the market that promise to increase fuel efficiency, but very few are worth having.

Unless you're a regular on the Forbes list of the world's billionaires, the chances are that, at some point, you've been concerned about the cost of putting gas in your car. According to AAA, the national average price is $2.52 per gallon, with Texas and South Carolina residents having the cheapest gas at only $2.28 per gallon (sorry, Hawaii—you have to pay the highest at $3.50 per gallon). These prices are still a heck of a lot better than the highest recorded average of $4.11 per gallon back in 2008, but it's still a plenty big chunk of change.

Updated March 2022: Decreasing your car's fuel consumption is more beneficial than ever. Although many vehicles have done a great job of ditching gas and moving to hybrid or full EV, many are still at the mercy of the pump. That's why we've updated this list to include more bogus ways of saving fuel and some additional mods that actually work.

It's a given that drivers have other expenses in their lives than just filling their cars with gas, and so, every dollar that we can free up from the fuel pump is one we can spend elsewhere (yes, we know guacamole is extra). Therefore, it's no surprise that many people take steps to increase their fuel efficiency. For example, consider hypermiling, a driving method for maximally increasing your vehicle's energy efficiency. Standard hypermiling techniques include accelerating and decelerating slowly, following the speed limit, and avoiding busy roads.

But is there anything else you can do to put your gas guzzler on a diet? Thousands of mods on the market promise to do just that. Unfortunately, these mods make a lot of outrageous claims. How do you know which ones are worth it and which are just gunning for your wallet? Fear not—we're here to help.

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Engine oil helps lubricate internal components of the engine to help it run most efficiently. The factory determines the weight of the oil or viscosity based on their standards, yet a simple swap could help save money at the pump. Many vehicles use conventional oil to lubricate parts, but synthetic oil is more effective at providing lube where it's needed most.

Though full synthetic oil is up to three times as expensive, the swap is generally worth it. The synthetic oil doesn't break down as fast, it's more consistent, and less energy is lost through heat. We say to spring for the pricier oil change for these reasons alone. Plus, you'll be doing fewer oil changes in the long run!

It's pretty well-known that our stock exhaust systems limit the car's performance. This reasoning has led many to swap out their stock system for an upgraded kit. Whether it is a cat-back, a complete system, or straight pipes, car enthusiasts have been changing the limiting options and going for something better.

While this is a great idea to unlock more power from your engine, it won't improve gas mileage. In fact, because these systems look to utilize the gasses escaping your car, you will likely see a drop in mileage. It's worth it for those looking to gain extra speed, but be prepared to shell extra cash at the pump.

Serpentine belts help use the energy from the engine to power vital systems like air conditioning, water pumps, and cooling fans. The problem is because they rely on a mechanical function, it takes efficiency away from the engine. Removing the belt entirely wouldn't be an excellent experience for the driver, though.

To combat this extra wear and tear on the engine and the reduced mileage, many have converted the mechanical systems into electrical systems. This way, the battery takes most of the work, with the alternator being the single component that will still need the power from the engine. We guess the world really is going electric!

Fuel magnets claim to increase the efficiency of your vehicle by breaking up fuel molecule clusters into smaller, more combustible fragments. Simply place the magnets around your fuel line about two inches from the engine, so they say, and you'll instantly see a 24% improvement in MPG.

These handy tools also supposedly eliminate carbon and varnish deposits, thus saving wear and tear on your engine. And all this can be yours for the low price of $7.99. Okay, really? Not to get too scientific, but at the chemical level, gasoline is an alkane, which is a tree-like structure of hydrogen and carbon atoms, neither of which are magnetic. In fact, there are only four metals that are considered magnetic: iron, nickel, cobalt, and manganese. And none of these are used in gasoline. In the end, fuel magnets do nothing but waste your $7.99.

This is a page from the hypermiling playbook. Make your vehicle as utterly and ridiculously aerodynamic as it can possibly be. This includes reasonably simple mods, such as using grille blocks and truck-bed covers and removing bike racks and mud flaps. But if you really want to go aerodynamic to extremes, you can also remove door handles, badges, antennas, and windshield wipers. Front license plates and side mirrors should be removed for ultra-aerodynamic efficiency, but this is sometimes illegal, depending on where you live. And don't forget to cover over any holes left behind.

It's a philosophy akin to how tiny drops of water, when combined, make a mighty ocean. Combine these mods with a hypermiling driving technique, and you'll definitely be visiting the fuel pump less often in the future.

These weird little shark fins supposedly reduce drag and increase downforce, turning your sad little daily driver into a weekend racing machine! Or not so much. They pretty much only increase the efficiency of your car in the same way that having light-up shoes as a kid made you run faster—in other words, only in your imagination. Don't believe us? If cars, planes, and different types of vehicles are regularly tested in wind tunnels, why haven't any of the engineers begun adding these to their production vehicles?

Yet, we're sure the company selling these self-adhesive plastic bits for $14 absolutely had them evaluated in a wind tunnel first (*sarcasm alert*). So, if you like the look of them, install and enjoy them by all means. But don't have any illusions that they'll manage to accomplish something that all those aerodynamic engineers somehow failed to do.

According to the US Department of Energy, aggressive driving can lower your fuel efficiency by up to 40%. That's where the ScanGauge OBD II Monitor comes in. By using one of these easy-to-install, relatively inexpensive tools (around $130-$160 depending on how good of a deal you find), you'll get real-time observations on your MPG. This'll allow you to polish your driving habits to achieve maximum fuel efficiency.

When you're given immediate feedback that your lead foot is costing you actual, real money, you'll probably be encouraged to be a bit more gentle with the gas pedal. The same goes for slamming on the breaks, idling in traffic, and driving at inconsistent speeds. How are you going to spend your 40% fuel savings?

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Water-injection kits actually do serve a purpose. If your car has an engine knock due to pre-ignition, a condition in which the fuel ignites prematurely, a water-injection kit can help cool things down and delay ignition. But now, let's talk about what water injection won't do.

It won't slow the rate at which your car burns fuel, so it won't make your vehicle more fuel-efficient. It won't make your car faster, even though drag racers use it (for the reason mentioned above). And even worse, because most cars have a preferred fuel-to-air ratio, simply introducing water without doing something else to maintain that ratio will just make your vehicle perform worse. Instead, why not put that water to better use and wash your car?

The US Department of Energy estimates that 3% to 11% of fuel consumption of the light-duty type is used to combat rolling resistance, which the definition is "the energy lost from drag and friction of a tire rolling over a surface." You may already be able to improve your MPG with the tires you currently have, though. Simply inflate them to the recommended levels in the owner's manual, and according to the DoE, you could improve your fuel economy by 3%. But if that's not quite enough, you can look into low-rolling-resistance tires.

Designed to ease the car's movement, these tires can save you up to $78 per year in fuel costs, according to Consumer Reports. But considering the tires themselves will cost you quite a bit more than $78, it really only makes sense to switch if you're in the market for new tires anyway.

Cold-air kits come from the same line of thinking as water-injection kits. If you cool things down, so they say, you'll burn fuel slower and make your engine more efficient, and have a magical talking unicorn for a best friend. Okay, they don't really say that last part, but they may as well because it's all just wishful thinking.

Cool-air kits seek to pull air from outside the engine compartment because it's, well, cooler. They have long tubes with weird bends to accomplish this, but what ends up happening is that the airflow into the engine becomes inconsistent, which reduces power and efficiency, especially if your motor has a Mass Airflow Sensor. It turns out cold-air kits are just full of hot air.

To be honest, this entry is both legit and crazy. If you're a super eco-conscious person with money to burn, you could put solar panels in your vehicle. Rather than power the car, the panels collect energy to help with start-up, which reduces stress on the alternator. Less stress over time adds up to a more efficient vehicle.

But since these panels are insanely expensive (around $10,000!), it doesn't make a ton of sense to spend that kind of money just for a tiny bit of added engine efficiency. However, the technology is still progressing, and in all likelihood, one day, this will be a completely legitimate way of powering our vehicles. I'm not here to tell you what to do with your money, so if you like the idea, then go eco-wild.

This entry comes from the same place as the vortex generators. Some spoilers and body kits do improve the aerodynamics of your vehicle, thus increasing your fuel efficiency. But these types of mods have been rigorously tested by the manufacturers and are usually priced as such.

So, if your front bumper lip comes in a self-adhesive roll that you got off the internet, odds are it's not going to be all that helpful. Or if that spoiler is a one-size-fits-all model, it's going to be about as successful as one-size-fits-all pants—which is to say, not at all. In fact, hypermilers often remove spoilers to save weight. So, if your goal is to look cool, then do whatever you want. But if your goal is to increase MPGs, step away from the body kits.

Unless you own one of those cars from ye olde days that you start with a hand crank, your vehicle is nothing without its electrical system. Everything from your stereo to your air conditioning to your throttle, which, of course, controls fuel flow, is all connected via wires and fuses to the battery's negative terminal.

Over time, these wires wear out, which means the electrical systems in your car have to work that much harder to get things done. That's why it's worth it to invest in quality grounding wires and cables. If you keep your car's electrical systems in tip-top shape, you won't be wasting extra fuel because your throttle was lagging. Plus, good grounding wires are pretty affordable, so it's really a no-brainer.

This story is pretty much pure urban legend. Once upon a time, an unsuspecting man buys a new car. He drives it as normal but begins to notice something strange happening: no matter how much he drives, the car never seems to need more gas. In fact, he eventually realizes that the car has gone 200 miles on a single tank.

In some versions of the story, he takes it back to the dealer who "fixes it" (i.e. removes this magical super carburetor) and returns the car. In other versions, the dealer recalls the car and gives the man a replacement. In still other versions, the man goes outside just in time to see mysterious figures running away with his car's carburetor. Whichever version of the tale you prefer, the Miracle Carburetor is probably off living somewhere with Bigfoot and the Loch Ness Monster.

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Did you know that for every extra 100 lbs your car totes around, your vehicle will use 1-2% more fuel? Well, now you do. But before you toss your kids out, let's look at a few other ways to help your vehicle run lean and mean. For starters, take out everything you don't need. Those bags of cat litter you've been toting around? The golf clubs you left in there from last weekend? It's all gotta go. Now, if you're really up for a challenge, you can take things even further.

Gas weighs 8 lbs per gallon, so depending on how big your tank is, only filling it halfway could easily save you 50 lbs or more. If you rarely have passengers, why do you need a back seat? Get rid of it—as if you needed another excuse not to drive your mother-in-law around.

Acetone (a colorless, flammable liquid) has a lot of uses, typically in medicine, in chemistry, and at home as a solvent for removing things like paint and nail polish. But according to the internet, you can also add it to gasoline (500:1 gas to acetone ratio) to slow the combustion of your fuel and increase your MPG by 25-30%.

Actually, here's a spoiler: anything that says it can improve your gas mileage by huge amounts is usually complete crap. But because we like scientific proof, the MythBusters tackled this theory in their episode titled "Exploding Trousers." Shockingly, their findings showed that adding acetone slightly reduces your MPG (probably because cars aren't actually made to run on paint remover). For the record, they also tested fuel magnets and a miracle carburetor and found both to be completely worthless.

The most aerodynamically efficient shape at subsonic speeds is one with a rounded front and sharply tapered tail (think of a cross-cut of an airplane wing). But if you look at any car on the road, you'll notice that no vehicles have that shape. Are we all missing out on potential MPG savings just because our cars are the wrong shape?

Well, if you're really determined to squeeze every mile possible from your fuel tank, there's a way to fix that. You can mod your car into a Kammback, which is a design with a square back end (rather like a hatchback), or you can go all the way into a full boat tail. EcoModder tested the design and found an approximate 15% improvement in fuel efficiency. You'll just have to get used to explaining that to all the people who ask what the heck you did to your car.

Contrary to what its name would have you think, spark plugs don't actually create any sparks. Instead, they provide a space for the electricity generated by the ignition coil to travel via the electrodes sticking out of one end. Spark plugs are crucial to the operation of your engine, and from time to time, they must be replaced when they wear out or get corroded.

The main advantage of high-performance spark plugs is that they conduct this current more efficiently, which means they last longer and don't need to be replaced as often. But that's where the helpfulness ends. Spark plugs, good or bad, won't affect the performance of your engine itself. They either work, or they don't. So, go ahead and invest in the high-performance ones if you hate changing the things, but otherwise, it's a hard pass.

Thanks to our love of fried foods, there's no shortage of WVO (waste vegetable oil) just sitting around in need of recycling. So, why the heck aren't we all driving with it? If you have a diesel vehicle, you can simply pour WVO (after you strain it, of course) into your tank, and go, but because it's more viscous (a.k.a. thicker) than diesel fuel, it'll damage your engine over time.

The best thing to do is to get a professional conversion that consists of a two-tank system: one to store diesel, which is needed just for starting your car, and the other to heat oil and send it to the engine. Are you going to get more MPG than you would with regular fuel? Probably not, but you'll be saving money and helping the environment, so we're counting that as a win on all fronts.

What would you say to a mod that can eliminate your emissions, clean your engine, and save you huge amounts on your gas bill? I'd say it's too good to be true. And when it comes to engine ionizers, that's exactly the case. These devices purport to use electrostatic energy to rearrange the electrons in the fuel molecules so that they take on a negative charge.

The theory goes that the molecules will then repel each other (meaning, they'll have more air between them), which supposedly improves the efficiency with which the fuel burns. I hate to break it to you, but this is a lot of pseudosciences. When Popular Mechanics tested one such device, they got a 15 bhp reduction. Then, they had to end the test when the ionizer caught fire. And I'm pretty sure you can't save fuel when your car is on fire.

Michael Stroup is an emerging author with experience writing for academics and personal portfolio pieces. Articles featuring JDM cars have been popular on his website. His love for cars combined with a passion for writing creates content that is engaging and fresh! Michael's hobbies include snowboarding and family time.