Is premium gas better for your engine

Personal finance coaches say that one path to helping balance your budget could be as simple as giving up your daily latte macchiato. The little things help. Like not splurging on what your car drinks.

Premium-grade gasoline is the most expensive gas you can usually buy, costing about 50 cents a gallon more than regular. Because only about 18 percent of new cars sold in the United States need it, there is no advantage in performance, fuel economy or emissions control for the other 82 percent to use high octane.

It’s no small matter. AAA estimates that drivers, who may think they are giving a gift to their beloved cars, waste more than $2 billion a year buying more octane than their vehicles require. Gift wrap nicer floor mats instead.

Gasoline is a lot like wine: A higher price does not assure greater satisfaction. The basic guidance, as always, is to follow the automaker’s fuel requirement in the owner’s manual, although it may waffle, saying that high-octane fuel is recommended (but not required), leaving the decision to the driver.

Octane explained

Still, if the car requires premium, that’s what you should buy to keep the engine in peak tune. The octane rating posted on the pump is a measure of the fuel’s resistance to detonation — combustion gone rogue inside the cylinders. In cars from 1980 and earlier, the condition could be heard as pinging or knocking — the sound of stones rattling in a tin can.

Recently, the quest by automakers for increased efficiency and power has resulted in engines with higher internal operating pressures, accomplished by raising the compression ratio, adding a turbocharger, supercharger or both.

Under those conditions, the formulation of premium gasoline with an octane rating of 91 or more is needed to assure that combustion in the cylinders is kept under control. The higher the octane, the greater its ability to prevent the unruly type of combustion engineers call detonation. The goal is to ignite the fuel mixture solely with the spark plug, rather than from the heat in the cylinder, to prevent detonation, which can seriously damage high-performance engines.

An engine not as highly stressed that is designed to burn 87-octane gas doesn’t run much risk of detonation, so it gains no benefit from using premium. In those cars, the five or more extra dollars spent on premium for each tankful is simply wasted, the equivalent of feeding Zabar’s pumpernickel to the Central Park pigeons.

“If it doesn’t say ‘required,’ it’s fine to go with the lower grade,” said Jason Kavanagh, senior vehicle test engineer at Edmunds.com, the car-shopping website. But, he added, you should test the economics for yourself.

One comforting note: Even when premium is required, using a tankful of lower-octane gas in a pinch is unlikely to do mechanical damage because of a bit of electronic wizardry called a knock sensor, which was introduced in the 1980s as part of computerized emissions control systems. Performance will suffer as the system compensates for the reduced octane, however.

A list of cars, from 2012-18, that require premium gas is online at the Edmunds website. For 2018 models, the 18 percent that require premium has held relatively steady over the years. The number of cars for which premium is recommended was 16 percent, a figure that has steadily grown over the last decade because of higher compression ratios, and more turbochargers and superchargers.

Say goodbye to winter gas

Another factor in pricing that motorists will soon encounter is the switch to summer gasoline blends. Yes, gasoline is seasonal, just like your wardrobe. And just like the weather across the United States, the timing of the switch and the fuel’s chemical makeup will vary.

The basic idea is that the summer gasoline formulations, which arrive as early as this month — but must be in place by June 1 in most areas — are formulated to reduce volatility. This measure of how readily it evaporates (and contributes to ground-level smog) is expressed by the gasoline’s Reid vapor pressure. Winter blends, conversely, need to evaporate more easily for quicker starting in cold weather; they return after Sept. 15.

There’s really no way for drivers to avoid the extra cost of summer gas — a dime or more per gallon, depending on the location — which is a result of the ingredients in the blend and the need to shut down refineries for the changeover. The summer chemistry does have a slightly higher energy content, so you may see a small improvement in fuel economy.

Higher ethanol levels

There is another wrinkle you’ll want to be aware of this year.

The limit of ethanol content in summer gasoline blends has long been capped at 10 percent — the typical level in most gas sold in the United States, known as E10 — because of ethanol’s relatively higher volatility. The E.P.A. is proposing to lift the ban on higher concentrations in summer gasoline, allowing the ethanol level to rise to 15 percent, or E15.

That means motorists will have to read the signs on the gas pump more closely.

Here’s why: The E.P.A. approves E15 for use only in light-duty vehicles of 2001 model year and newer. E15 is not approved by the agency for use in pre-2001 vehicles or motorcycles, boats, lawn mowers and off-road small engines.

More important, while 93 percent of 2019 model vehicles (by sales-weighted volume) are approved for E15 use, according to the Renewable Fuels Association, some automakers explicitly do not want you to fill up with it. New vehicles from Mazda, Mercedes-Benz, Mitsubishi, Volvo and some from BMW and Subaru, are not approved for E15 by their makers. Vehicles made by Fiat Chrysler, Hyundai, Kia and Volkswagen from model years before 2019 may also not be approved for E15, so you’ll have to dig out that owner’s manual again.

The warranty implications vary by manufacturer; using E15 may void the warranty for the engine. As always, it’s smart to be aware of what you’re putting into the tank. And there’s some chance that E15 may not arrive at your gas station this summer in any case, as ethanol refineries have been out of action as a result of flooding in the Midwest.

Smarter Driving is a new series all about how to buy, own, drive and maintain your car better. Have something you’d like us to cover? Reach out to Smarter Driving’s editor, James Schembari, at .