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.
Rubber and plastic engine components were likewise formulated to withstand gasoline, but not ethanol. “We made the transition in the 1980s,” Reid says. “Elastomers and compounds in O-rings, gaskets, fuel lines [were] redesigned for ethanol.” What about engines built before then? If an engine hasn’t visited the mechanic much in two decades, the switch to E10 might be a good time for longterm maintenance items such as replacing hoses, rebuilding carburetors or checking fuel pumps. But assuming normal maintenance, neither Reid nor any mechanic interviewed sees a need to rebuild fuel pumps, carburetors or other components before they act up. “If it’s my money, I’d run it,” Reid says. “If it starts to act funny, doesn’t run quite like it always did, then I’d take it in for service.”
Ethanol does have innocent victims. My brother-in-law filled his 10-year-old 30-foot center console with E10 and then ran to his slip. A few days later my wife and I ran the boat barely two miles before deteriorated hoses choked its 225 Optimax outboards to a sputter. While the boat shouldn’t have fallen victim to ethanol, our Florida Keys vacation was a fatality. The inner liner of the fuel hose simply fell apart, clogging the fuel system. Jim Lawrence of J&B marine in Tavernier, Florida, had seen it before. “I found particles and pieces in the [fuel] filter,” Lawrence says. “Particles from the fuel tank should be flat, but these had a radius to them. When I pulled the hose off, it was pretty obvious.” In fact, rubber hose deteriorations are plaguing Floridians on boats only three years old.
So why does ethanol attack supposedly resistant hoses? “Ethanol changes the chemical environment,” Kelley says. Years of soaking in ordinary gasoline and exposure to heat, cold and sun also affect hose chemistry unpredictably. “It would be awfully difficult to replicate [those conditions in a laboratory],” Kelley says. Still, he doesn’t see this as the likely cause for hose problems in South Florida. Instead, he blames phase separation, which occurs because polarized water molecules bond with polarized ethanol. In small quantities, the two stay suspended in gasoline, but add too much water and the mixture separates and settles. “We’ve always had phase separation. When you don’t have ethanol, it can take a few parts per million to get phase separation,” Kelley explains, meaning water in the bottom of gasoline tanks years ago also contained polar compounds from the gasoline. “With E10, instead of a few hundred parts per million of something coming out of the gasoline, it’s more like 5,000, 6,000, 7,000 parts per million. There’s no place for that amount of material to hide.”
Kelley says the resulting cocktail expands anywhere from two to eight times beyond the original volume of water. “It gets sucked up into the engine. It doesn’t burn, and the combination of water and ethanol is extremely corrosive.”