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To earn Top Tier certification a fuel must pass four tests – deposit control on intake valves, fuel injectors and combustion chambers. Beyond that, it must also prevent intake-valve sticking. Basically, it’s gas with extra cleaning agents designed to keep engines running their best. Think of it as a housekeeper for your cylinder heads.

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Gasoline is an impure substance refined from a very impure base stock – crude oil. It’s an explosive hydrocarbon cocktail containing all kinds of different chemicals. In addition to its own molecular variability, refiners and retailers incorporate additional substances into the mix, from ethanol alcohol to octane enhancers. Still, gasoline contains even more additives, some of which are designed to prevent harmful deposits from forming inside engines.

According to Bill Studzinski, Fuels Technical Specialist at General Motors, a number of OEMs saw this problem and got together to push for higher levels of detergency. He said Top Tier gasoline is a better fuel for engines, and that it takes the mystery out of what a good fuel is and what an average fuel is.

Chris Martin, a spokesman for Honda said “we’ve supported it [Top Tier gasoline] because we’ve seen a benefit from it for our consumers in the long run.” He also said the average driver doesn’t know about detergent additives, they just look for the cheapest gas available but “Top Tier fuel goes a step beyond that.”

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“We don’t require that our vehicle owners use Top Tier gas” Martin said, but it helps “make sure the engines are going to last as long as they could.” This is obviously beneficial, especially since Honda drivers historically keep their cars for a long time.

Responding to questions via e-mail, Marie Valentine, the Senior Principle Engineer, Vehicle Regulation and Certification Engineering, Toyota Technical Center, said the amount of detergents in Top Tier gas is about twice what’s required by the EPA. However, it can vary depending “on the base gasoline and the chemistry of the detergent additive.”

When asked about the price of Top Tier Valentine wrote, “Toyota does not comment on the true cost. However, generally there is no change between TTDG [Top Tier Detergent Gasoline] and normal LAC [Lowest Additive Concentration] gasoline,” good news for consumers wanting to keep their vehicles for many years.

Top Tier is all about keeping engines clean. As far as fuel economy is concerned, it should perform identically to gasoline with lower levels of detergent, so don’t expect a big efficiency boost.

From a big-oil perspective, Top Tier hasn’t necessarily caught on. Some of the largest players in the industry have adopted it including Shell, Chevron and Conoco, but not all.

ExxonMobile, the world’s largest oil refiner, is one of the companies onboard with Top Tier. All of their retail gasoline sold in the United States meets the standard, having received formal certification back in 2010.

Top Tier gasoline must contain more deposit-fighting detergents, it also must be sold at all of a fuel marketer’s stations and across all grades of its gasoline, from 87-octane regular to top-of-the-line premium. Additionally, to earn the seal of approval fuels cannot contain metallic additives, which are potentially harmful to automotive emissions-control systems.

Simply put, Studzinski said Top Tier gasoline is “a higher level of detergency, which keeps your engine running optimally.”