AAA hired an independent lab to complete 4,000 miles of simulated driving to compare Top Tier gasoline with the cheaper blends. Their findings show that the additive packages in Top Tier gas resulted in fewer carbon deposits than those found in the non-Top Tier gasoline test.

The study also found that there were some secondary benefits to the better additive packages, including slightly better fuel economy and better drivability. The benefits are apparent, but do consumers really care?

The Top Tier gasoline specification was created by a group of automakers in 2004 in response to the minimum gasoline detergent standard introduced by the EPA in 1995. The EPA standard was designed to meet emissions targets but didn’t account for engine longevity. So, automakers created a new higher standard to prevent long-term issues such as clogged fuel injectors and contaminated combustion chambers.

Top Tier gasoline is widely available and can even be found at wholesale retailer Costco. Most gasoline comes from similar sources and is transported along the same pipelines until it reaches a local distributor. The distributor sells the gas to local stations and blends in an additive package based on the brand and specification. Some gasoline gets a very basic additive package but Top Tier gas gets a very specific package that has been tested to meet the Top Tier standards.

According to the AAA study, the non-Top Tier fuel caused carbon deposits that were 19 times higher than the deposits from the Top Tier fuel. They also saw better drivability and better fuel economy when the better fuel was used. Emissions were also reduced, likely due to the ban of metallic additives in Top Tier fuel.

The laboratory completed the test on a Ford port injected 2.3-liter engine, which appears to be the Lima engine from the late 1980s. This engine has been used for testing for about 15 years and is a popular one, due to the orientation of the valves (which shows the difference in carbon deposits in just 100 hours of testing). The full report shows compares the average 34.1 milligram carbon deposit in the Top Tier fuel test to the average 660.6 mg carbon deposit in the non-Top Tier fuel test.

The technical results are clear but the second part of the study looks at whether they really matter to consumers. The AAA survey found that 63 percent of drivers who responded believe that quality of gasoline differs between retailers, but only 12 percent use the additive package as a deciding point when making a purchase. The two main things that actually drive purchase decision are the location of the gas station and the price of fuel, with almost three quarters of respondents saying those factors motivated them the most.

Although the study makes it seem like your engine is doomed if you use lower-level fuels, there is an upside. Switching to a Top Tier gasoline has shown reductions in carbon deposits on an engine previously run on lower level gasoline, and the cost difference to switch is only a few cents per gallon. It may be worth it to make the jump.

[Images: AAA]