Personal Finance

My father was an all-gas-is-the-same guy who considered it a personal failure if he filled up at one station only to see gas sold for a few cents less down the road. For decades, I followed his price-only approach, but recent research has changed my mind.

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Now I look for Top Tier gas. Even if you’re unfamiliar with the term, you’ve probably bought some at the pump. Almost all of the major oil-company and refiner brands of gasoline are certified to be Top Tier, a standard established by a consortium of the world’s biggest carmakers (who in turn recommend it for their cars).

Although all gasoline is federally required to have chemicals that keep your engine clean, the Top Tier program says the products it sanctions have a higher concentration (and better mix) of these detergents. And an independent study by AAA bears out the claim that these fuels can keep an engine from developing harmful carbon buildup, which can cut fuel efficiency and performance.

So why wouldn’t you buy a Top Tier gas? Well, price. Gas often costs less at the independent outlets that don’t opt for certification. In my case, my genetically programmed pursuit of the absolute cheapest gas was a hard behavior to give up. But during the 12 months of its study, AAA found that Top Tier gasoline was just 3 cents more expensive than uncertified fuel, on average. And grocery rewards programs are often coupled to Top Tier brands, so signing up for one could earn you discounts that nullify the price difference.

Pricey premium. Once you’ve pulled up to a Top Tier pump, you face another decision: What grade? Regular, plus and premium are the usual choices, though some brands have more or give them special names. The grades reflect a numeric value for octane, a measure of the fuel’s resistance to igniting at the wrong time in your engine (a bad thing that you may hear as “knock” or “pinging,” a sort of light rattling sound on acceleration). And higher octane is more expensive.

A funny thing happened on the way to today’s lower fuel prices: The price differential between regular and premium gas soared. In late August, the average gallon of reg­ular cost $2.38; premium was $2.88, or 21% more. That’s about double the historical gap, and because the average driver spends more than $1,000 a year on fuel, premium’s premium is hundreds of dollars.

Fuel experts point to a number of factors for this trend, but one is that more cars on the road today prefer premium. Why would a carmaker specify premium? One way to meet rising fuel-economy requirements while satisfying consumers’ desire for more horsepower is to build highly tuned, often turbocharged, engines that deliver optimum performance when fed higher-octane gas.

As ever, start with the owner’s manual. If it lists regular gas (normally 87 octane), great. Do not waste your money (as millions do) on premium. Using premium will not help you pass an emissions test, and your beloved old hooptie will not consider extra octane that it doesn’t need a “treat,” like whipped cream on cocoa or something. If your manual specifies higher octane, see if it’s required or just recommended.

If it’s recommended, feel free to pump regular and save money. You might notice slower acceleration, or you might not. Will your gas mileage suffer? We doubt it. While it’s hard to get numbers with so many models out there, Consumer Reports found no loss in several vehicles they tested.

If required (common among brands such as BMW and Porsche), things get murky. We’re loath to contradict the owner’s manual, but many owners have recounted using regular gas without trouble. With these high-performance engines, you’re more likely to notice a power loss on lower octane. And if you’re going to try to scrimp, keep your ears open for the telltale sound of engine pinging. If you hear it for more than a second or two, go back to premium.

You can follow David Muhlbaum’s automotive musings on twitter at www.twitter.com/daveydog.

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