Does the Type of Gasoline You Use Really Matter?

gasoline pump photo

If you’re paying too much at the pump, read on as our Mechanic Next Store explores the mysteries behind gasoline pricing and octane ratings.

When it comes to gas for your vehicle, is it all the same? Is there a difference between the “name brands” of Exxon, Mobil, Shell versus the “grocery store gas” at Kroger or WalMart or even the less common “off-brand” names sold at discount stations with odd-sounding names that include “Kangaroo,” “Pure,” or “Liberty”?

And what about the different grades of gas available at starkly different prices. Call it what you will – regular, mid-grade, premium, 87, 89, 93, or even “V-Power” if you happen to be filling up at a Shell station. By choosing one fuel over another, are you risking damaging your engine in the interest of saving money?

Let’s start with the easy answer. Unless the station attendant is bringing your gas out in a metal bucket or dispensing it from a pump with a glass globe on top so you can see the “quality” or lack thereof, like they did at the earliest gas stations, there’s little difference in quality no matter where you buy gas. Gas quality today is regulated and legally required to contain certain levels of detergents, octane, ethanol and other ingredients. And while “name brand” gas might contain more engine-cleaning detergents, there’s a good chance that the gas found at “off-brand” stations was actually produced by the same name-brand manufacturers you know. Save some money and buy gas where it’s convenient for you and easiest on your wallet and comfort level.

The bigger, and age-old question and debate on most motorists’ minds is, “do I need to spend more money on a higher grade fuel, and if so, which one, and why?” There are generally three grades of unleaded gasoline available at nearly all U.S. gas stations, regardless of name, with the price per gallon rising in tandem with the fuel grade. Depending on what you drive, these grades matter.

To make an informed decision, you need to first understand what those numbers mean. The results might surprise you. Spoiler alert – a higher number doesn’t necessarily mean the gasoline supercharges your engine.

The three numbers in question are simply octane ratings, which mean nothing to most drivers unless they’re a chemical engineer, or work in the petroleum industry. When crude oil is refined (cracked) into gasoline and other byproducts, the end results are products composed of hydrocarbon chains of varying lengths. For example, methane has one carbon atom, propane has three, hexane six, and octane eight. Thanks to Mother Nature, it turns out that octane – technically iso-octane – with its eight carbon atoms and 13 hydrogen atoms, resists detonation really well, as compared to, say, heptane, which ignites fairly easily. An 87-octane rating means the gas is composed of 87 percent octane and 13 percent hexane and/or other ingredients. Pushing the “91” button at the pump delivers gas that’s 91 percent octane, and so forth. You get the picture.

Fascinating – but what’s this got to do with your engine, and possibly saving some dollars at the pump? Simply put – as the octane rating goes up, so too does the gasoline’s ability, when mixed with air in the engine’s cylinders, to withstand compression without spontaneously detonating or igniting. In gasoline engines, the air/fuel mixture inside the cylinder is supposed to ignite only when a small flame is sparked by – you guessed it – the spark plug. As that small flame gradually grows and spreads out within the cylinder, the air/fuel mixture should ignite in one detonation. Problems arise, mainly in the form of an audible “knock”, when more than one detonation occurs within the cylinder. And that “knocking” or “pinging,” or “pinking” if you’re in the U.K., can be more than just an annoyance and rob your engine of power – it can also destroy it, quickly or over time.

As that initial flame grows, pressure and heat within the cylinder rise. Under the right circumstances, those increases will cause the air/fuel mixture that hasn’t yet been reached by the flame to detonate, resulting in two detonations – one from the flame and a spontaneous one from the increased pressure and heat. The knocking sound results.

Most modern vehicles have knock sensors on the engine that can tell when a knock is about to occur and can adjust the spark’s timing just enough to prevent the premature explosion. A higher octane fuel is better able to withstand the increased pressure or compression, thus preventing spontaneous detonation.

Does your vehicle need higher octane?

But that doesn’t answer the question of which engines need higher octane fuel. It’s a question with several answers. For starters, high-performance engines need higher octane fuel. That’s because the engine’s designers engineered it to generate higher compression within the cylinder and increased power. Higher pressure and lower octane, however, isn’t a good match.

To help determine what octane rating your vehicle needs, start by looking in the owner’s manual. Other good sources are two lists in this article that specify which vehicles require premium gas and those for which it’s just a recommendation. For example, Acura’s MDX, RDX and RLX are all on the “premium-required” list, as are Audi’s A4 through A7, several BMW models, Chevy’s Camaro and Corvette, the Dodge Viper, and numerous other vehicle manufacturers and models. On the “premium-recommended” list are again Acuras and Audis, Ford’s Escape, Subaru’s WRX and several Volvos. High-performance engines that require a higher-octane fuel and don’t get it will deliver decreased power and performance.Gas prices photo

Still other drivers determine whether they need a higher octane fuel through experimentation. If the vehicle runs great on 87 with no knocking, pinging, or performance issues, and choosing the lower grade fuel doesn’t run afoul of any warranty requirements or specific manufacturer guidelines, why spend the extra money on a higher octane fuel?

Knocking or spontaneous detonation can be caused by other factors as well. For starters, the environment can be the culprit. Areas with high temperatures and low humidity can increase knocking and the need for higher octane. So too can vehicle age. Older vehicles can have a buildup of carbon within the cylinder, creating hot spots that lead to pre-ignition. These deposits can also decrease cylinder volume leading to higher pressures. Other culprits include a malfunctioning EGR system that increases cylinder temperature or an improper or malfunctioning spark plug. Increased load – like those that occur when towing or during steep uphill climbs – higher RPMs, or a malfunctioning cooling system that results in higher engine operating temperatures can also bring on the knocking.

Leaded gas and older vehicles

Many drivers will remember another choice available at the pump in addition to the three grades available today – leaded or unleaded fuel. Around the 1920s, a partnership between GM and ESSO, now Exxon, discovered that adding tetraethyl lead (TEL) to fuel helped raise the octane ratings above what they were listed at by increasing the compression ratio. Leaded fuel also came with the added benefit of helping protect soft valve seats, like those found in many 1970s-era vehicles and earlier.

During engine operation, heat from combustion gases causes valves to temporarily weld themselves to valve seats, if only for a tiny fraction of a second. Each time the weld between the two is broken, minute metal pieces from the soft valve seat are torn away, attaching to the valve. Over time, these deposits oxidize and further harden, inflicting damage on the valve seat as the valve continually hammers down. Lead in fuel helped prevent the two from welding, reducing valve seat recession or wear. Unfortunately, lead – which was spewing from the exhaust of millions of vehicles worldwide by that time – is bad for the environment and devastating to human health, which is why it was gradually phased out beginning in the 70s.

Fuel additives

That begs the question of what’s a 1970’s muscle-car owner to do to prevent damage in the absence of leaded fuel, short of spending a lot of money to install hardened valve seats or replace a cast-iron head with an alloy one? For starters, don’t overwork your engine, turn consistently high RPMs, or let her get too hot. And, consider adding a lead substitute with anti-wear properties to your gas tank.

For the rest of you, consider using one of the countless octane boosters available, most of which are designated as being safe for turbos, oxygen sensors and catalytic converters, if your vehicle needs it.

And remember two things. If you hear some knocking and there’s no one at your door, it might be time to switch to a higher octane fuel. On the other hand, if the vehicle manufacturer doesn’t specify high octane and there aren’t any performance issues, save some money by sticking with a lower octane fuel, and purchasing it where you want.

Editor’s note: Whether you need a lead substitute, octane booster, fuel additives or even a new engine, stop by Advance Auto Parts is here to help. Buy online, pick up in-store, in 30 minutes.

How far can you really go on empty?

gas_gauge_emptyOh, how we wish we’d thought of this!  You know when that pesky little light goes off on your dashboard? No, not the “check engine” light. At Advance Auto Parts, we know exactly what to do with that one—just pull on up to one of our stores and ask a Team Member to use a code scanner to help diagnose the likely problem.

We’re talking about that other light—the one that tells you that you’re almost out of gas! The one that makes you ponder either stopping for gas immediately, or driving around another several days. Recently, we were able to track down some statistical evidence that may help you make a more informed decision. Check it out at:

It’s a simple little site that gathers facts and stories from car owners about how far their car will go after the empty gas tank light comes on.

Here’s the information they’ve gathered on my good ol’ Acura CL.


If I’m reading this right, seven people have said their Acura CL will go 60 miles before it’s really out of gas! I don’t know about that.  Hmmm, now I’m really going to have to pay attention. I’m on day number two right now, but I’ve only driven about 20 miles. Most people voted in the 35-45 mile range for this particular vehicle. Ah well, we’ll just have to see.

Make sure to check out the site—some of the stories are pretty funny, too.

When you’re done, just remember, if you need a new gas cap, or fuel treatment to maintain optimal performance for whatever gas you do still have, stop by an Advance Auto Parts store, or shop online.

We may not be able to tell you exactly how far you can drive, but we can help ensure that you’re safe and secure on the road, using the best auto parts possible.

So, how far can you go?  Tell us in the comments section!

Fuel for Life

I’ve always loved cars. And since my Dad was constantly involved in automotive projects of one form or another, my exposure to DIY came early on. From my initial oil changes, I eventually graduated to full-on rebuilds and restorations. Now, as Dad’s long moved on, I generally tend to be the guy in the neighborhood that friends and neighbors look to for advice on things like safe driving and maintenance. No surprise, in the last year particularly, they’ve been asking me how to save money on gas. While fuel prices as of now (Summer, 2012) seem to have peaked or are actually going down a bit, they’re still pretty high and there’s reason to believe that they will continue to rise over the long run. Fortunately, here are a few tips to save gas that will also hopefully make you a safer driver.

First and foremost, maintain your manufacturer’s recommended tire pressure. It saves wear and tear on your tires and will help you meet the fuel mileage targets of your car. Auto manufacturers have highly trained engineers who match specific tires to specific cars for a balance of ride, handling and fuel economy, so it’s best to adhere to their specs. Plus, it’s one of the easiest things to do to check and refill air. My wife used to always leave these sorts of things to me, but once I showed her how easy it was to check her tire pressure, she now insists on doing it every couple of weeks. (Of course, I still have to take out the trash.)

Underinflated tires may give you a slightly smoother ride, but they’re more likely to blow out and they will negatively affect your fuel consumption.

Another way to achieve good gas mileage is to drive with anticipation, which is good practice for safe driving anyway. By that I mean, think a few moves ahead, like a chess player rather than focusing only on the car ahead of you. This will help you avoid fender-benders or worse yet, a major accident. Look ahead when you drive, so you won’t be doing things like suddenly speeding up right before traffic slows on the highway. The more time you can spend at a steady speed (cruise control), the less your engine will have to work and the more fuel you can save.

Try to keep your car as aerodynamic as possible. It’s summer, so you’re traveling with your family, but if you can fit things in the car instead of in a giant roof rack, your car will cut through the air more easily and save fuel because the engine won’t have to work so hard. And for that matter, there’s no need to pack your entire house into your car. Pack smart. Less weight equals better mileage.

For that matter, clean out your trunk. It’s good to have some safety items like extra water and a blanket, but remember—extra weight is the enemy of fuel economy.

Try to maintain a steady speed also. Trust me. Since I’ve been married I tend to drive more conservatively (particularly when my wife is in the car) but I used to be Larry the Leadfoot. And, I was spending a LOT more money on gas. Gas mileage limits are set not only for safety, but because driving fast uses a lot more fuel than driving at a more moderate pace, and you won’t really get there that much faster anyway.

If you put even these simple tips to use, you’ll be amazed at how you can cut down on trips to the gas station and best of all, save money.

Learn more about ways to boost your fuel economy.

Fuel additives: do they work and, if so, what’s the best fuel additive?

You may be wondering if fuel additives are really effective and if they really work as well as advertisements claim. The reality is that there are benefits to using them, but it’s important to be realistic in your expectations.

The EPA requires that all fuel sold in the U.S. contain a certain amount of deposit-control additives to prevent a dangerous buildup in your car’s systems. However, a type of fuel could meet the bare minimums mandated by law — but it still may not provide an adequate level of prevention. This is where the effectiveness of fuel additives comes into play.

You want to choose a fuel additive that can keep your engine clean if you purchase the cheapest gas possible.

With today’s gas prices, most of us are looking for the cheapest gas, rather than completely focusing on the health of our vehicle — and that focus on prices is understandable.

To protect your vehicle, look for fuel additives that contain polybutene amine (PBA), which can clean out deposits from carburetors, fuel injectors and intake valves, as well as potentially a few other areas. They also may be able to restore your engine’s overall performance and help lower your carbon footprint.

Don’t overdo. Using too much of a particular fuel additive can actually cause damage, such as ruining sensors and other car features.

Then, you will end up spending more in the long run than you would have dealing with typical deposit damage.

The bottom line: choose a fuel additive that is appropriate for your vehicle and use it according to directions. This can help save you time, money and hassles in the long run. To save more money, find the cheapest gas in your area.