AAA’s research showed non-Top Tier fuels left behind 19 times more carbon deposits on intake valves than Top Tier brands.AAA reports that it hired an independent laboratory to test six gasoline brands, three of which were Top Tier certified. Gas rated at 93 octane was used, because AAA reports that more additives are usually found in fuels with that rating.
The Top Tier fuel program was formed in 2004 by the Center of Quality Assurance in Michigan following concerns from automakers who pointed out engine problems related to carbon build-up from low-quality fuels.
Prior to receiving Top Tier certification, a station must first meet the program’s detergent requirements and pay a fee. Most major brands of gasoline, such as Amoco, Chevron and Exxon are Top Tier certified.
So, do Top Tier fuels really make that much of a difference?
Yes, and in a big way, according to AAA. Controlled laboratory tests conducted on an engine dynamometer reveal that non-Top Tier fuels left behind 19 times more carbon deposits on intake valves than Top Tier brands.
Carbon measurements were also taken came from cylinder heads and piston heads. Other issues that non-Top Tier fuels presented during the 100-hour tests included rough idling, hesitation, knocking and pinging, a drop in fuel efficiency and a marked decrease in emissions performance.
“Testing has shown that running an engine on a non-enhanced additive package fuel can roughly double carbon monoxide emissions (180-200 percent rise) and cause a 20-30 percent increase in hydrocarbon emissions,” the report states. “These emission increases were measured ahead of the catalyst over the course of 55 hours of dynamometer testing that equated to approximately 2,000 miles of real-world driving.”
The good news is that after running the engine for the equivalent of 1,000 miles on a Top Tier fuel, emissions were brought back to normal.
Depending on engine type and use, carbon deposits can lower fuel efficiency from 2 to 4 percent, the report states.
AAA does not identify the brands of fuels that were tested. Fuels were chosen at random among major gasoline retailers in southern Texas.
As called for under ASTM D6201 fuel testing, a Ford 2.3-liter fuel injected engine was used to perform the carbon tests. The engine was run 100 hours for each test, which is considered the equivalent of driving 4,000 miles.
The study also includes a survey, which in part states that while 63 percent of polled drivers acknowledge differences in the quality of gasoline, only 12 percent of drivers will buy fuel based on detergent additives.
Three out of four respondents said the main reason for choosing a gas station is location or convenience, while the second most important reason, according to 73 percent of those polled, is price.
EDITOR’S NOTE: Tom Quimby is the associate editor of Hard Working Trucks, a sister publication.
