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Do I Need to Use Engine Oil or Fuel Additives?

202406 do I need to use oil or gas additives scaled jpg Fuel additive | illustration by Paul Dolan

Under normal circumstances, most modern engine oil and gasoline brands work fine on their own to keep your engine running smoothly. But there may be cases where even the best of them could use a little help with an additive.

Related: Do You Really Need to Change Your Oil Every 3,000 Miles?

Fuel Additives

One of the most common fuel additives is gas-line antifreeze, which is typically methanol, a type of alcohol that absorbs the water that results from condensation forming in the air at the top of the fuel tank when it’s cold out. If that water gets into the gas, it can freeze and clog up the fuel line or fuel filter, causing the car to run poorly or not start at all. (If you’ve ever heard that you should keep your tank at least half full in the winter, this is why; it reduces the amount of air at the top of the tank, which in turn limits the amount of condensation that can form.) However, most gasoline sold now contains 10% ethanol — which works much the same as methanol in this regard — so adding a bottle of gas-line antifreeze doesn’t always carry the benefits it used to.

Another common fuel additive is octane booster, which is sometimes used in cars that require high-octane gas, such as high-performance models, or vehicles that “ping” a bit under acceleration when using the manufacturer-recommended grade of fuel (which is usually listed inside the fuel door and in the owner’s manual). In the latter case, the “pinging” is typically caused by a problem such as excess carbon deposits in the engine’s combustion chamber. But in either case, it’s often cheaper and certainly easier to just buy higher-octane gas at the pump. However, if your tank is fairly full — perhaps accidentally filled with a lower grade of gas than recommended — using an octane booster might be worthwhile. In this situation, you won’t be pouring in the additive before filling the tank, so it might be wise to drive gently until cornering, stopping and accelerating have helped mix the additive into the fuel.

Fuel-injector cleaners were once very popular and often needed, though most current name-brand Top Tier gasolines likely carry enough detergents to keep your fuel injectors clean. Some cleaners also claim to remove carbon deposits in the cylinders, which in excess can cause the “pinging” mentioned above. If you’re experiencing rough running or the occasional light pinging, it might be worthwhile to try a fuel-injector cleaner before taking your car to a mechanic. (Any frequent or loud pinging, however, should send you straight to the mechanic.) Be careful to read the instructions on how much to use, as you may want to put in a full bottle and not fill your tank all the way to get a stronger cleaning mixture.

Finally, fuel stabilizer is often used in engines that see only seasonal use, such as lawn mowers and snow blowers, but it can also be used in cars that sit for long periods, such as classics that aren’t driven in the winter or a snowbird’s car that isn’t driven for months at a time.

Note that, when possible, it’s always best to pour in any fuel additive before you fill the tank with gas to ensure that the additive mixes thoroughly with the fuel.

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Oil Additives

Many oil additives are derided as “snake oil,” as they often don’t cure any problems and may even cause some. Modern engine oils contain their own additives that work together to keep your engine in top shape, so adding anything to that can throw off the balance. For instance, some aftermarket additives may reduce friction, but they can make the oil thicker so that it doesn’t flow easily when the engine first starts — when most wear occurs — and may prevent it from sliding between parts with close tolerances.

Thus, a widely accepted rule is that you should change your oil regularly with a good-quality, name-brand oil of the right viscosity (which is usually noted in the engine compartment and/or owner’s manual and will be something like “5W-30”), as the additives formulated into the oil degrade over time; the additives may also be present in the same quantities from the start in “cheap” oil. Synthetic oil (a quality upgrade over conventional oil) has many advantages that may make it worth its relatively small extra cost. And if your car is older, using an oil specifically labeled for high-mileage engines can also be helpful, as it typically contains special additives that help worn engines.

Nevertheless, there are people who swear by certain products that may help with specific problems. These might include cleaning an engine’s internal parts (crud can build up over time, particularly if the oil isn’t changed regularly), quieting noisy valve lifters (which can sound like a light tapping noise) or stopping small oil leaks (by slightly swelling the rubber gaskets or seals). An internet search for “test of oil additives to stop oil leaks,” for instance, can help you find such products. Certainly these will be questionable, but if you see the same products recommended by multiple reviewers, that might be a good sign. However, you’re still messing with the oil’s viscosity and additive balance, so you should use these products with caution.

Also, as with fuel additives, it’s important to read the instructions. Some oil additives, for instance, might advise putting in the additive roughly 100 to 300 miles before doing an oil change (and that might be in fine print, so read carefully), which means the engine isn’t supposed to be run for a long period on the treated oil. It’s also important to note that you do not want to overfill your oil, so before pouring in any additive, make sure the oil level is low enough to accept any amount you’re planning to add from the container. In some cases, you may need to drain or remove some oil before pouring in the additive (hand-operated vacuum pumps for doing the latter aren’t very expensive, and they usually include a small-diameter hose that can go down the oil-fill tube).

In most cases, you shouldn’t need any additives as long as you’re changing your oil regularly with a high-quality oil of the right viscosity and filling your tank with good-quality gas. While an engine oil or fuel additive might help with certain problems, they can only do so much, and they certainly can’t fix a mechanical failure. However, they may be worth a try if the $10-$20 for a bottle pales next to the hundreds of dollars it may take for a mechanic to dive into it.

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