Perhaps you have seen the advertisements on national television (in the U.S.) for a type of gasoline called “Unleaded 88” or “Regular 88” and wondered whether you should use it in your vehicle. The ads, of course, emphasize the positives of the fuel, including a higher-octane rating (compared to regular unleaded, typically 87 octane), lower emissions, lower price and potential performance improvements. Do these claims have merit? The short answer is yes, but the benefit to an individual driver is likely to be quite small. The gains to society, in aggregate, are much more significant. 

Unleaded 88 is regular unleaded gasoline blended with up to 15% ethanol. All gasoline in the U.S. (even premium grades) can contain up to 10% ethanol. One way to classify gasoline is by the maximum amount of ethanol that it may contain, so the usual unleaded grades (typically 87, 89 or 91 octane) are all E10, Unleaded 88 is E15 and a grade specifically for flex-fuel vehicles called E85 can contain up to 85% ethanol. You should only use E85 if your vehicle is specifically designed for its use, while all the major automobile manufacturers have stated that E15 is safe for any of their vehicles beginning with the 2001 model year. 

So it’s safe, but is it a good idea? Let’s look at the potential advantages. First, is there any benefit to a higher-octane number? This is tied to the claim of better engine performance. If your vehicle has an engine knock sensor, and if you frequently run the engine at wide-open throttle (i.e., “pedal to the metal” or the accelerator fully depressed), you might get a slight increase in power output under those conditions. If not, or if your vehicle is designed to run on premium unleaded, switching to E15 is unlikely to improve performance and could actually hurt your vehicle if it requires premium fuel.  

Next, during the combustion process, it is likely that fewer oxides of nitrogen will be produced, since the higher amount of alcohol reduces the peak combustion temperature. However, the catalytic converter likely reduces these pollutants to a negligible level in any case. There will be a small decrease in carbon dioxide emissions, since the alcohol molecule contains less carbon than the other fuel components. 

The price is lower, as ethanol costs less by volume than gasoline and also is currently subsided by the federal government. The actual price differential will vary with time and location, but E85 is typically 3%- 5% less than E10. So far, so good—however, ethanol contains only about 75% of the energy content of gasoline, so an additional 5% ethanol reduces the energy content of the blend by a little over 1%. Experiments to determine the effect on vehicle mileage generally confirm the decrease, but an individual driver would be unlikely to notice as mileage is influenced by so many real-world factors (vehicle weight, tire pressure, outside temperature, etc.) that everyday mileage varies by considerably more than 1% over time. It does suggest, however, that you should only buy E15 if the price is at least 1% less than E10. 

Lastly, although E15 is recommended for motor vehicles made after 2001, it is not recommended for other uses, such as lawnmowers, snowmobiles, chain saws or other motors that are subject to seasonal use. This seems to be primarily due to ethanol’s affinity for water, which can cause moisture to accumulate during long-term storage and contribute to corrosion. 

So go right ahead and use Unleaded 88 in your 2001 or newer vehicle, unless the manufacturer recommends premium fuel instead. Take comfort in the fact that you are saving money (as long as the price is more than 1% lower), burning less gasoline and reducing carbon emissions (at least marginally)!

Ed Becker is a Fellow and Past President of STLE. He is currently president of Friction & Wear Solutions, LLC and can be reached through his website at www.frictionandwearsolutions.com.