What is the Best Fuel to Use in Your Car or Truck and Why?

Will premium gasoline make your car run better? Can regular gasoline damage your engine? Does midgrade give you better gas mileage? Motorists often ask these questions and come up with the wrong answers. This short article will help you decide what kind of fuel to put in your car.

The Short Answer

Use the cheapest fuel for which your car's engine is designed. You'll find the minimum octane rating in the owner's manual, and cars that require premium fuel will usually say so on or near the gas cap. If your car specifies premium fuel, use the good stuff. Otherwise, there's (usually) no reason to buy anything but regular 87-octane fuel.

The Long Answer

Gasoline is rated by octane. Generally, regular fuel is 87 octane, the premium is 91 or 93, and midgrade is (surprise, surprise) somewhere in the middle.

To understand what octane means, we first have to look at the concept of preignition. Engines compress a mixture of air and fuel and ignite them with a spark. Under certain conditions, the fuel-air mixture can ignite early, which makes a knocking sound, this is called preignition.

Nowadays, most cars have knock sensors that prevent preignition, so you'll rarely hear it.

Octane measures the gasoline's resistance to preignition, the higher the octane, the less likely it is to detonate. Contrary to what some believe, high-octane gasoline has the same energy content as low-octane gasoline.

Why Do Some Cars Need High-Octane Fuel

Some high-output engines use a higher compression ratio in order to produce more power. They compress the fuel-air mixture to a smaller size, which creates extra heat that can cause the fuel to pre ignite. These high-compression engines need high-octane fuel to ensure the gasoline doesn't ignite early. If your car has an engine that requires premium fuel, it will say so in the owner's manual, and there will usually be something written on or near the gas cap.

When to Use Regular Gas

If your car is designed for regular 87-octane gas, you're in luck: You can safely use the cheap stuff. Premium fuel won't make the engine run better or produce more power.

There's no benefit to buying premium fuel, at least not to you or your car, the gas station owner and the oil companies benefit plenty.

When to Use Premium Gas

If your car says "premium fuel required" and the owner's manual specifies 91- or 93-octane, then you should always fuel up with the good stuff. Back in the day, using low-octane gasoline in a car that required premium would likely cause damage. In a modern car, the knock sensor can retune the engine on the fly to avoid preignition, but this will most likely reduce power and fuel economy, so it's a false economy, and engine damage is still possible.

When You Can Take Your Pick

If your car says "premium fuel recommended," you have a choice, you can run regular or premium. These engines generally develop more power and get better fuel economy on higher-octane fuel, although the difference may be slight. However, you won't damage the engine (or void your warranty) by running regular. Our advice: Run a few tanks of both regular and premium, and calculate your fuel economy. Decide for yourself if the differences in power and fuel economy (if they're even noticeable) are worth the extra cost of premium fuel.