Regular vs. Premium Gas, Redux

Source: By Norman Mayersohn, New York Times • Posted: Tuesday, October 1, 2019

Readers responded to Smarter Driving by scratching their heads over the fuel economy of premium gasoline, while others who admitted that they never used turn signals blamed the other guy.

Jim Wilson/The New York Times

We got mail.

Since the Smarter Driving column began in February with an article about the importance of snow tires in winter, we have received hundreds of emails from readers who have weighed in on the issues we covered, including turn signals and gasoline grades. We replied to all of them. Here is a deeper discussion of those topics.

It was not much of a surprise that the gasoline column received such a strong response, given that the choice of brands and grades is a source of debate among many car owners. Coke vs. Pepsi, Marvel vs. DC.

Let’s clear the decks, starting with a bit of a recap: In April, we explained that pumping premium gas into a vehicle whose engine requires only regular did no favors for the car, the owner’s budget or the environment. High-octane fuel in a low-octane car does not substantially improve performance, increase fuel economy or cut emissions. It’s wasteful, the “equivalent of feeding Zabar’s pumpernickel to the Central Park pigeons” we said.

Readers thanked us. And readers also told us we were wrong.

Some said that their miles per gallon improved with premium gas. Yes, that can happen, but that’s not the same as fuel economy, which must include the higher cost of premium to be a valid measure of economy. Those extra miles cost more.

To be certain, I asked AAA engineers to run the numbers, and they came to the same conclusion that the m.p.g. improvement would not nearly offset the price difference between regular and premium. They’ve done controlled lab tests, running premium in cars whose makers recommended (not required) premium. Mileage improved 2.7 percent, and horsepower increased 1.4 percent; premium prices averaged 20 percent more than regular on Sept. 18, according to AAA.

Enough already. There are other matters relating to your car’s drinking habits we need to talk about.

It turns out that spending a bit more for gasoline that meets Top Tier standards, which define gasoline detergent levels, does offer a smart return for any engine. Introduced in 2004, the formulations in Top Tier, which is supported by 10 major automakers, are designed to reduce the buildup of deposits inside the engine, which can hurt performance.

Research by AAA showed that carbon buildup on intake valves after tests that simulated 4,000 miles of operation was 19 times higher with non-Top Tier gas than on engines using gas containing Top Tier detergent additives. The cost increase for Top Tier gas was about 3 cents per gallon, AAA found. A separate test showed that switching to Top Tier gas would also remove existing deposits.

AAA’s report also concluded that “long-term use of a gasoline without an enhanced additive package can lead to reductions in fuel economy of 2 to 4 percent, drivability issues and increased emissions.” Other potential problems caused by carbon deposits include hesitation, rough idle and knocking.

Marketers that comply with Top Tier standards certify all gasoline grades to the detergency standard and display the standard’s logo. At its website, there is a list of Top Tier retailers. It also certifies diesel fuel.

Octane at altitude

A few readers of the April article asked about octane requirements at high altitude, with Ben from Colorado and Angela from New Mexico noting that in parts of their states regular-grade gasoline has an octane rating of 85 or 86. That’s an issue for owners of cars whose makers specify a minimum octane number of 87.

According to the E.P.A., 85 octane fuel “was originally allowed in high-elevation regions, where the barometric pressure is lower, because it was cheaper and because most carbureted engines tolerated it fairly well.” The lower pressures inside the cylinders let engines run acceptably on 85 octane without incurring detonation.

Things have changed. While modern gasoline engines use electronic controls to detect detonation and adjust accordingly, it’s still smart to stick with the recommended fuel for your vehicle. There are warranty implications, of course, but it’s also a good plan considering the widespread use of engines that derive their improved performance from a turbocharger or supercharger. Those devices raise cylinder pressures, providing a boost despite the thinner atmosphere at high altitude.

Ethanol concerns

The potential ill effects of ethanol in gasoline are worrisome for owners of cars whose makers specify limits on acceptable levels of ethanol. The typical breakdown is 90 percent gasoline and 10 percent ethanol, know as E10. Most automakers approve it for use in their newer vehicles, although most have not approved the higher concentrations, such as E15. Ethanol is also a concern for owners of older vehicles, motorcycles and outdoor equipment.

If you want to buy zero-ethanol gasoline, a good first move may be checking websites like that list stations selling it. Nonethanol gas is not widely available, so a workaround is using an additive that will inhibit fuel-system corrosion caused by ethanol, which is alcohol-based.

Much of the problem caused by ethanol in gasoline — is that alcohol absorbs water. The humidity in the air, absorbed and accumulating in the gas tank, is enough to incite mayhem in an engine (and condensation in the tank will have the same effect). The engine can digest small amounts of water, but a buildup causes problems, especially when it separates into a pure water layer in the tank.

Another helpful strategy is to keep the tank as near to full as practical when the car will be parked for a long period. With less air in the tank, there’s less moisture for the alcohol to absorb.

Turn signal strategy

In June, Smarter Driving reminded readers of the importance of using turn signals when making a move in traffic — and O.K., there was some hand-wringing over the diminishing use of this important (and legally required) safety feature.

A thank you goes to the readers from around the country who pointed out one reason drivers switch lanes without signaling, especially on crowded highways: The blinking light tips off surrounding drivers, who then zoom ahead to block the merge. We’re talking about an intentional, unsafe behavior in a specific circumstance, not an impolite oversight.

A number of readers, understandably, were miffed about getting cut off by feisty drivers who take their daily commute as a contact sport. John, a reader who works in Manhattan, wrote: “I like to joke that using your turn signal in N.Y.C. is a sign of weakness.”

For safety’s sake, the best plan is to let those aggressive drivers go. But there are a couple of defensive practices you might want to keep in mind. First, don’t use the turn signal casually, as if testing the water. Signal once you’ve made sure the space alongside is clear and you are actually ready to initiate a lane change. Then, be sure you have the momentum to make the merge without having to wait for a match of speeds. Do it smoothly and decisively. Dawdling in a lane with your turn signal blinking can baffle other drivers.

If the brat in the adjacent lane wants to bully you out of the space, so be it. We’re talking steel at speed here, not a video game. Just wait for the next clear opening.