Top Tier Detergent Gasoline

Top Tier Detergent Gasoline is a performance specification and trademark designed and supported by several major automakers — BMW, General Motors, Fiat Chrysler Automobiles, Honda, Toyota, Volkswagen, Mercedes-Benz, and Audi (as of 2017^[update]). Top Tier gasoline must maintain levels of detergent additives that result in a higher standard of engine cleanliness and performance as compared to the EPA requirement. In addition, Top Tier fuels may not contain metallic additives, which can harm the vehicle emission system and create pollutants. Each of these automakers recommends the use of Top Tier Detergent Gasoline in their owner's manuals. As of 2017, Top Tier Detergent Gasoline is available from 51 licensed retail brands.

Licensed Top Tier Detergent Gasoline (TTDG) retailers use a higher level of detergent additives compared to other non Top Tier retailers using only the minimum EPA required detergent additives in order to help prevent the buildup of harmful engine deposits which may reduce fuel economy and optimal engine performance. According to an automotive industry spokesman, the regular use of this type of gasoline results in improved engine life.

The Top Tier standards must apply to all grades of gasoline that a company sells, whether it is economy (low-octane) or premium (high-octane).

Detergent additives serve to prevent the buildup of engine "gunk," which can cause a host of mechanical problems. Automotive journalist Craig Cole writes, "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."

While General Motors' fuels engineer Andrew Buczynsky states that no one has identified the exact molecule in gasoline that causes engine buildup, he asserts that consistent use of Top Tier Detergent Gasoline will keep engines cleaner. Engine gunk typically builds up in fuel injectors and intake valves, causing reduced fuel efficiency, acceleration, and power, as well as increasing emissions, rough idling, tendency to stall, and increased motor repairs. When fuel injectors accumulate deposits, they do not distribute fuel evenly, creating pockets of too much fuel and too little fuel. Too-little fuel around the spark plug dampens the combustion that drives the piston downward and may cause a misfire. When the frequency of misfires reaches a certain point, the on-board computer turns on the "service engine" light on the dash. The repair for this type of problem depends on the severity of the deposits. In milder cases, a mechanic may solve the problem by adding a can of fuel-injector cleaner into the gas tank. However, in some cases, the fuel injectors must be replaced. If the deposits have formed on the intake valves, they may be removed via walnut shell blasting. In severe cases, a more costly cylinder-head rebuild may be necessary.

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