Premium vs. Regular: What’s the Right Gas for Your Car or SUV?

Gasoline all smells the same. It’s the wrong stuff for lighting charcoal grills, and more likely to flash and burn you. And it’s confusing (slightly) about what gasoline to use in your car, SUV, or pickup. Here’s what you need to know about buying gasoline for your car. Further down, we’ve also got information on buying gasoline for yard tools such as snowblowers, lawn mowers, and chainsaws. Also for buying diesel fuel for vehicles.

Premium gasoline helps some not all engines develop more horsepower. But not more mpg. (Photo: BP. Main photo: Bosch)

Using Premium vs. Regular Gasoline

In a nutshell, buy the gasoline your owner’s manual calls for. That means regular for cars using regular, or 87 octane; and premium for cars using premium, meaning 91 or 93 octane. We’re citing the octane numbers posted on pumps; there are other ways to report octane as well.

Write this on your palm: Buying 91- or 93-octane premium won’t benefit a car designed to run 87-octane regular gasoline. The octane rating is the measure of the fuel’s ability to be compressed before it self-ignites without the spark plug. Premium can be compressed more, resulting in a bigger bang when the spark plug goes off, and more downward pressure on the piston and crankshaft, so it delivers more power. But engines aren’t variable compression (except Infinitis with the new VC-Turbo system), so a car designed for regular compresses fuel to the point where regular won’t self-ignite. It won’t take advantage of premium’s power potential. Running premium in a mainstream sedan or crossover doesn’t improve fuel economy, either.

It used to be the case that premium gasoline had extra detergent additives to keep the engine, especially the valves and injectors, cleaner. Now the additives have to be in all grades of fuel of every gasoline provider selling Top Tier (which covers nearly all the major US retailers and stations; see below for more info).

What about using regular in a vehicle that calls for premium? You shouldn’t do it. But it depends on the automaker’s wording:

Premium fuel recommended means that’s what you ought to use. If you put in a tankful of regular, the engine’s knock sensor will dial back the ignition timing to avoid premature self-ignition (also called knock, or pre-ignition) of the compressed air-fuel mixture. Knock doesn’t sound like a knock on the door or like hammering; it’s more like a gurgle or rumble you may not even notice. You’ll get 5-10 percent less horsepower with regular, though fuel economy shouldn’t be affected.
Premium fuel required means don’t use regular. Period. If you wind up with a tank, or half tank, or regular, the engine-management computer’s knock sensor will still protect you by adjusting the ignition timing or air-fuel mixture. But don’t floor the throttle. You could add a can of octane booster, but note that some boosters contain carcinogens and/or ethanol.

Cadillac’s CTS-V – think Corvette for four passengers – requires, not just recommends, premium fuel for its supercharged 640-hp V8 engine. But why would you try to save five bucks filling the tank of a $100,00 car?

If someone tells you he (usually it’s a he) got better mileage running premium in a car meant for regular and got higher mpg, ask him if he ran an A/B comparison test over the same course. You’re hearing barroom talk. (Readers who disagree: That’s why the Comments section lies below.)

In short, current cars with knock sensors should be capable of dealing with octane levels below the recommended fuel. Older cars without knock sensors would suffer damage from continuous use of regular gas in a car meant for premium.

Trademarked Top Tier gasoline is a guarantee you’re buying good fuel. But good luck finding if an independent station has Top Tier. There’s no requirement the logo be on pumps. Employees may not know and some may say “Yes” as is “Yes we have gasoline.” (Image: Top Tier. Main image, above: Bosch)

Look for Top Tier Gasolines

A consortium of gasoline companies has banded to sell high-quality gasoline using the industry-wide trademark Top Tier. It calls for an enhanced package of detergent additives. Most majors pump Top Tier gas and every gas station bearing their logo will be Top Tier. But not every major is Top Tier (just most of them). Costco is a Top Tier seller but not currently BJ’s or Sam’s Club.

All of the top 10 gasoline retailers, by service-station count, are Top Tier: Shell, Exxon, Chevron, Speedway, BP, Circle K, Mobil, Sunoco, Valero, and QuikTrip. They account for more than half of all gasoline sales (57 percent of market share), according to the Oil Price Information Service (OPIS).

A test by AAA found significant differences between Top Tier fuels and those without the additives in Top Tier. Among the brands tested, AAA says in its report, “Non-Top Tier gasolines caused 19 times more engine deposits than Top Tier brands after just 4,000 miles of simulated driving. Such carbon deposits are known to reduce fuel economy, increase emissions and negatively impact vehicle performance, particularly on newer vehicles.

Here’s a full list of Top Tier stations in North America. If you don’t have the list, just google “top tier gas.”

Engine valves tested with and without Top Tier gasoline. (Image: AAA)

Top Tier Gas and Diesel Stations 76 (USA)Aloha (USA)Amoco (USA, Canada)Arco (USA, Canada, Mexico)Beacon (USA, Canada)BP (USA, Canada)Breakaway (USA, Canada)Break Time (USA)Cenex (USA)Chevron (USA, Canada, El Salvador, Guatemala, Honduras, Panama)Circle K (USA, Canada)Citgo (USA, Canada)Conoco (USA)Co-op (Canada). Co-op Diesel (Canada – select locations only)Costco Wholesale (USA, Canada, Mexico). Costco Wholesale – Diesel (USA, Canada – select locations only)Couche -Tard (USA, Canada)CountryMark (USA)CountryMark PLUS (USA)Diamond Shamrock (USA, Canada)Energy (Mexico)Esso (Canada)Express Mart (USA – Wisconsin)Exxon (USA)Fast Fuel (USA). Fast Stop – Diesel (USA – select locations only)Fast Stop Express – Diesel (USA – select locations only)G500 (Mexico)Hele (USA)HFN – Hawaii Fueling Network (USA)Holiday (USA, Canada)Irving Oil (USA, Canada)Kirkland Signature Gasoline (USA, Canada, Mexico). Kirkland Signature – Diesel (USA, Canada – select locations only)Kwik Star (USA, Canada)Kwik Trip, Kwik Trip Express (USA, Canada)Mahalo (USA)Marathon (USA)Metro Petro (USA)MFA (USA)Mobil (USA, Canada)Ohana Fuels (USA)Petro-Canada (Canada)Phillips 66 (USA)Puma (El Salvador, Guatemala, Panama, Puerto Rico)QT (USA)QuikTrip (USA)Ranger (Ranger Mustang, Ranger Stallion, Ranger Thoroughbred) (USA, Canada)Reeder’s (USA)Shamrock (USA, Canada)Shell (USA, Canada, Puerto Rico)Sinclair (USA, Canada)Sunoco (USA, Canada)SuperAmerica (USA, Canada)SuperFuels (USA, Canada)Tempo (Canada)Texaco (USA, Canada, El Salvador, Guatemala, Honduras, Panama)Tri-Par Qwik Stop (USA)Valero (USA, Canada)Win Win (USA)Source: Top Tier Gas

If you pull into an independent station, ask if the station sells Top Tier. It would be nice to see a Top Tier logo on the pumps, but that’s optional. Be prepared for the station attendant having no clue about Top Tier. Keep on driving. If you are low on fuel, go ahead and fill up. The fuel likely came from a distributor servicing multiple stations and instances of bad gas — water in the fuel, or regular sold as premium — are still small.

Chevrolet Equinox SUV Diesel: Buy the diesel version and you’ll get 40-45 mpg on the highway, way better than the EPA’s 38 mpg rating. Diesel passenger cars and SUVs typical beat the EPA tests by a healthy margin (photo: Bill Howard).

Diesel Fuel

Sooty diesel smoke means engine problems, not dirty fuel (photo: Bill Howard)

Diesel fuel is injected at higher pressure than gasoline. Injector cleanliness is crucial for proper operation. There’s a Top Tier certification for diesel. But service stations may also sell diesel not meeting the Top Tier specs, or sell diesel for farm use (stripped of road use taxes, it’s much cheaper) that isn’t Top Tier. So for certified diesel, each pump must carry a Top Tier certification.

All diesel fuel sold for road use must be ultra-low-sulfur to meet air pollution requirements. This is the result of a long-running battle between Big Oil, which wanted more emissions gear on diesel cars and SUVs, and Big Auto, which wanted lower-pollution fuel. Big Oil lost, although most cars and trucks, to meet pollution limits, have to treat the exhaust with diesel exhaust fluid (DEF), also called AdBlue.

While automakers would like you to use their branded DEF, by definition, any diesel exhaust treatment must meet basic specs, so you can treat DEF as a commodity and shop by price. $5 a gallon, or $12.50 for a 2.5-gallon container is about right.

Diesel fuel is supposed to have a larger nozzle so you don’t mistakenly fill a gas-engine car with diesel. But that’s not always the case. There is no universal color for the rubbery surround on a diesel pump handle, though green or black is common, so make sure you take down the proper hose. The best way to tell the diesel pump is by the grease and dirt on the pump handle.

Diesel fuel is quite similar to kerosene, home heating oil, and jet fuel. In a pinch, you could use kerosene to keep a diesel generator going, but it’s not a good idea to put anything in a diesel car other than diesel fuel.

Snowblowers and other yard equipment that isn’t year-round should run on ethanol-free gasoline. Or add a fuel stabilizer. The same applies to cars parked for the off-season (photo: Bill Howard)

Gasoline for Snowblowers, Lawn Mowers, Leaf Blowers

Gasoline-powered yard equipment and portable gasoline generators are characterized by long off-seasons when typical gasoline with about 10 percent ethanol by volume added can degrade over several months. Do this:

Buy premium gasoline that is ethanol-free. Regular gas seldom is, while premium may be. Services stations with no-ethanol gas typically have signage indicating it.
Add a fuel stabilizer such as Stabil (one brand name) to extend the life of small-engine fuel.
Buy ethanol-free yard/garden engine fuel such as TrueFuel, $20-$25 a gallon. It has a shelf life (in the can or in your engine’s fuel tank) of several years.

Most engines for good mowers and snowblowers are four-stroke. You add engine oil separately. Two-stroke engines need oil added directly to the fuel tank, typically 1:50 (2.6 ounces per gallon of gas) or 1:32 (4.0 ounces per gallon). Two-strokes are cheaper, noisier, and on the way out because of pollution and noise issues.

When you’re done for the season, empty the mower/snowblower and run it dry. If you want to keep a little fuel in it, use the ethanol-free fuel. If you have a half-full container of gasoline, use it up in your car. If it’s really old, more than a year, take it to a town or county hazardous waste recycling day.

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