Ethanol sucks! It’s a common refrain on engine maintenance blogs and is echoed in chorus in boatyards, marinas and waterside watering holes. You know E10 well by now — 90 percent gasoline blended with 10 percent ethyl alcohol. It’s been making its way around the country by federal mandate since 2005. In the years since, we’ve heard that E10 preys on boats — decomposed rubber parts and even burned pistons are among alleged crimes. Other accounts vary from clogged fuel filters to corroded metal and deteriorating fiberglass fuel tanks. Sometimes problems appear only in specific regions for a few months and vanish just as quickly. Stolen fuel economy has been added as evidence of ethanol’s dark side. But is ethanol guilty on all counts? Rather than reiterating public opinion, we interviewed experts and even put ethanol to the test — comparing it with straight gasoline in a 150 Verado and in a GMC pickup — with surprising results.
To ascertain ethanol’s effect on performance, we ran separate tests of a 2008 Boston Whaler 180 Dauntless with the 150 hp Verado, once on E10 and again on ethanol-free gasoline. The ethanol-powered motor showed a slight fall-off in our performance tests. At maximum throttle, the engine running on ethanol dropped only 10 rpm from when it ran on gasoline. Acceleration time from a standstill to 30 mph was off by a 10th of a second — about 2 percent.
Our fuel-flow numbers resulted in a similar gap between ethanol and straight gas. Economy fell off with E10 at a rate of a half-gallon per hour difference at 3,000 rpm, or $2 for every cruising hour.
Mercury engineers weren’t surprised at our performance or fuel economy results. The company’s engines are tuned to hit horsepower, torque and fuel-burn targets with either E10 or unblended gasoline. “We’re actually calibrating our engines slightly richer to protect the customer who burns E10,” says Tim Reid, director of engine design and development for both Mercury and MerCruiser. This protection is needed because E10 contains oxygen molecules not present in straight gasoline. For a preset ratio of air and fuel, E10 burns leaner, increasing cylinder and exhaust temperatures. Adding a bit more fuel to richen the mix cools things down with E10, but wastes a bit of fuel when burning straight gasoline.
As for the charge of burned pistons, most engines that were built before E10 was being considered were tuned a bit rich from the start. While they might be damaged by higher blends of ethanol, E10 actually helps these engines run cleaner. “We’re monitoring parts [purchased] on these legacy engines,” Reid says, “but we’re pretty confident the legacy fleet is safe with E10.”
Remember that boats had fuel problems long before E10 came along, and that the vast majority of boats switched to ethanol without a hiccup. Those that didn’t caused the current stir. Many problems have arisen because ethanol is a polar solvent — electrically charged to make or break chemical bonds much the way magnets repel or attract each other. Gasoline is comprised of mostly nonpolar compounds.
“I think it’s the interaction that’s causing the problems,” says Frank Kelley, Mercury marine’s fuels and lubricants specialist. This interaction strips years of gasoline varnish from the inside of fuel tanks, rapidly clogging fuel filters. It also rankles engineers who for decades assumed strong polar solvents like ethanol wouldn’t find their way into fuel. High-end builders, for example, preferred fiberglass fuel tanks, since they would — and did — outlast aluminum tanks many times over. But ethanol breaks down polyester resins, destroying tanks built in the ’60s, ’70s and ’80s and ruining attached engines in just weeks.
By Vincent Daniello, Illustration by Wayne Roth