Putting Premium Gas in an Engine That Requires Regular? Stop It Now

Putting Premium Gas in an Engine That Requires Regular? Stop It Now

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.

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.

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.

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