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Ethanol and Older Engines

What is it about older boats that make them more susceptible to ethanol's well-known problems?

Mechanic Working on Boat Engine

Over the past few years — since ethanol has become common for boat engines — Seaworthy has received hundreds of calls and e-mails complaining about problems that ethanol has created for their engines. The majority of these inquiries have one thing in common: They concern older engines, those made before around 1990, and a high percentage of them involve outboard engines. Seaworthy talked to Ed Alyanak, Mercury Marine's manager of engine test and planning development, and Frank Kelley, Mercury's fuels and lubricants technical specialist — who between them have over 60 years of experience — to find out why older engines suffer more than newer ones and what owners of these engines can do to minimize the problems.

Boat engines comprise one of the largest segments of "legacy" engines in the country. Unlike cars, boats often operate for decades, which means that there are hundreds of thousands of older engines — many of which were built 20, 30, or more years ago — still churning the water. According to Alyanak, these engines were engineered and built without the knowledge that they would be vulnerable to new fuels in the future. "No one knew ethanol would be a common additive to gasoline 20 or 30 years ago. We designed engines to run on straight gas," he says. And it's not just the engines that are affected by ethanol. Alyanak says that hundreds of boatbuilders who designed the engines' fuel systems from the gas tank to the engine were also unaware of the future challenges from ethanol. And the very simplicity of older carbureted outboard engines seems to make them particularly susceptible.

The issues for older engines fit into three categories: old vulnerable components not designed for ethanol use, ethanol's ability to dissolve deposits, and its ability to absorb enough water to separate.

New Standards

In the mid-1980s, a committee made up of people from the U.S. Coast Guard, the Society of American Engineers (SAE), the American Boat and Yacht Council (ABYC), the National Fire Protection Agency (NFPA), and Underwriters Laboratories (UL) got together. Ethanol (known as gasohol back then) was being introduced for automobile use and it quickly became evident that it would find its way to boats. New standards for hoses were necessary since ethanol was known to attack rubber and plastics. The result was a standard called SAE J1527. Since 1984, all hoses approved for marine use in gas engines have had to be built to this standard and hoses marked "SAE J1527" are capable of withstanding ethanol blends. Hoses not J1527-compliant will quickly deteriorate, potentially causing dangerous leaks, and should be replaced immediately. Something else to consider: Fuel hoses don't last forever and those from the 80s — even if they are properly marked — should be replaced. Most manufacturers advise replacing gasoline fuel hose after 10 years, and any hose that is 20 years old is way past its life; all marine-grade fuel hose has its manufacture date stamped on it.

Plastic and Aluminum Problems

Corroded Aluminum Carburetor

Older aluminum carburetors tend to suffer from the corrosive effects of ethanol much more than newer ones, which are made out of more resistant alloys. Corrosion can block tiny orifices, causing hard starting and rough running.

Frank Kelley, Mercury's fuel specialist, says that other plastic and rubber parts on older engines are susceptible to ethanol as well. These include seals and O-rings in the fuel system and carburetors. "Rubber materials tend to get hard and brittle with exposure, which can cause problems with needle valves in carburetors," he says. Some of these rubber components can be partially dissolved with constant exposure to ethanol, and bits and pieces can be carried into the engine's fuel system, causing clogs and misfires. Some older boats may still have plastic fuel filter bowls, which will degrade with exposure to ethanol and could leak, spilling gasoline into the bilge (old plastic fuel filter bowls should be replaced immediately with metal bowls).

One other troublesome area, according to Alyanak, is aluminum carburetors. Before about 1990, carburetors were built with alloys that are much more prone to corrosion from ethanol. When ethanol contacts the older aluminum carburetor housings, corrosion can cause tiny orifices to clog, which results in hard starting and poor running, two of the most common complaints, especially from outboard owners. This is one of the most serious problems for older outboards because there is often no upgraded carburetor that can be fitted. The only effective solution is to run ethanol-free gasoline (see sidebar). Alyanak says that manufacturers now use new alloys that are far more corrosion resistant.

Non-engine-related problems on older boats involve the fuel-fill gasket, which with age and ethanol exposure can allow rainwater and spray into the fuel tank (more on that later), and fiberglass gas tanks. Not many boats have fiberglass tanks, which have been shown to leach out chemicals that can gum up intake valves and wreck engines. The leaching process also severely weakens the tanks, which in some cases has caused gasoline to leak into the bilge. The only sure cure is to replace the tank with an aluminum one.

Ethanol the Solvent

Another one of ethanol's properties that causes headaches for older boats is its solvent ability. According to Kelley, over the years, gasoline — especially gasoline that may be more than one season old — oxidizes and creates gums and sludge that coat the inside of fuel tanks and even hoses. When gas containing ethanol is introduced, it begins to dissolve the gunk, which is carried to the fuel filter. Initially, this is more of a nuisance since simply changing the filters a few times usually solves the problem. But anything that gets past the filter, or is already downstream of the filter, can cause havoc in the carburetor. Carburetors have tiny orifices that get easily clogged, leading to hard starting, rough running, or even a complete shutdown. Simply getting the carburetor cleaned or rebuilt is often just a short-term solution; preventing the gunk from getting to the carb again is critical. A finer grade filter (10 microns) will prevent most particles from getting to the carb, though the filters may clog up more frequently as the ethanol dissolves the gunk. (Carry spares and a galvanized bucket to keep old filters prior to disposal.) Any hoses that lead from the filter to the carburetor should also be replaced since they may have deposits inside them that get washed into the carburetor by ethanol.

Ethanol Loves Water

Ethanol is hygroscopic, which means it readily absorbs water. This is good news and bad. According to Kelley, the good news is that small amounts of water in gasoline are absorbed and simply get burned along with the fuel. The bad news is that gas with ethanol will keep absorbing water until there is so much that most of the ethanol and water will separate and sink to the bottom of the tank. This is called phase separation. The process is more common in older boats that may have had water in the bottom of the tank for years. Kelley says that once ethanol is introduced, the water — along with more that may be coming through a leaking deck fitting — will be absorbed and can eventually lead to phase separation. This leaves a layer of water/ethanol on the bottom of the tank. If the fuel pickup — resting at the bottom of the tank where the mixture is — picks up a slug of water, the engine will quit. If that isn't bad enough, there's more: "This water/ethanol mixture is quite corrosive, too, and aluminum fuel tanks are at risk of corroding from the inside if they are in contact with this stuff," says Kelley. Preventing water from getting into the tank is much easier than removing it so make sure the fuel fill gasket has a tight fit and keep your tank full — this limits the amount of water that can get into the tank from condensation. If you suspect you may have water in your tank, contact a company that specializes in cleaning out tanks. Seaworthy has reported on several insurance claims for damage and injuries caused by using improper equipment (such as a wet vac) to clean out a tank — leave it to the pros. Not sure if you have water in your tank? You can buy a product called Kolor Kut that's dabbed on the end of a stick and lowered into your fuel tank; it changes color on contact with water. One more thing to mention: Don't plug the fuel tank vent in an attempt to keep moisture out. It's doubtful much gets in that way and plugging the vent could lead to pressure in the tank, which could cause a spill.

More On Carburetors

"Carburetors are dumb," says Alyanak. "From the factory, they're calibrated to run on one kind of fuel and can't make adjustments on their own, like modern electronic fuel injection can." Engines that were built many years ago, before ethanol, were calibrated to run on straight gas, he says. "Ethanol has extra oxygen in it, which throws off the air/fuel ratio, making the engine run too lean," he says. Lean engines run hotter and have what are euphemistically called "drivability problems" — hard starting and rough running. It's possible, he says, to recalibrate a carburetor to tolerate E10; a good mechanic can do it. New carbureted engines come calibrated for E10.

Tips For Older Engines

  • Fuel-system components on older engines, those built prior to about 1990, should be inspected before starting the engine in order to identify any signs of leakage or corrosion.
  • Mercury's fuel expert Kelley says if you are going to run on E10 for the first time, check for the presence of water in your tank, which is common in older boats. Ideally, your tank should be empty of all fuel and water before you add E10.
  • Make sure your fuel-fill gasket doesn't leak, or rainwater and spray can get into the tank.
  • Don't add a fuel dryer, which is often ethanol — it will just compound the problem. Kelley recommends using a fuel stabilizer each time you fill up (also true of newer engines). Watch out, he warns: Some octane boosters contain ethanol as well — read the label before you add any. Incidentally, according to the chemical engineers, there is no way to recombine separated water and E10.

Ethanol, The Scapegoat

Ethanol has been blamed for everything from rough-running engines to high food prices. And while there are challenges to boaters using ethanol, it can't be blamed for everything that goes wrong. Here are some issues we've heard from boaters that weren't caused by ethanol:

"I haven't used my boat for four years but when I topped it off with ethanol last spring, it wouldn't start."

Four year-old gas — any gas — can gum up carburetors and prevent an engine from starting. (It's good practice to empty the carburetor completely whenever the boat is being laid up for more than a few weeks.)

"My boat won't get up on plane since I started using ethanol."

E10 has about 3 percent less energy than E0, which is hardly noticeable performance-wise. Something else — a nicked or bent prop, fouled sparkplugs, for instance — is a more likely culprit.

"Since I started using E10, my gas tanks are full of water!"

Ethanol attracts water from the air but it wouldn't likely be enough to cause phase separation — condensation and leaks from deck fittings can, though. Ethanol can cause the water to separate if there is enough already there. The best advice is to keep the tank topped off to reduce condensation, and make sure there is no way water can leak into the gas tank, either through the deck fill or sending unit cover.

"My boat gets vapor lock since I topped up with E10 last winter."

Winter blends of fuel have different vapor pressures than summer blends (whether they have ethanol or not). Vapor lock can be caused by using winter blends in hot weather so try to top off in the fall before winter blends are sold.

"My mechanic says the engine runs rough because of ethanol."

While E10 can cause some problems, especially in older engines, it's often used as an excuse when the real problem can't easily be found. Tired carburetors, faulty ignition systems, and worn engines can mimic the symptoms of E10 problems.

Finding Non-Ethanol Gas

The best way to eliminate the worry about the effects of ethanol on an older engine is simple: Don't use gas containing ethanol. Fortunately, that has become easier lately, with many marinas now stocking E0, and websites showing where it's available. Below are two sites that list non-ethanol gas — most are auto gas stations (available for trailer boaters), though marinas are listed too.

Before you fuel up at one of these places, you should know a few things. Gas composition tends to change quickly and the availability of E0 is dependent on whether or not it's available from local distributors, so be sure and ask the station if the fuel is still ethanol-free. Also, pump labels are not always reliable. Even though the pump states that gas contains 10-percent ethanol, it could be any number below that as well; it's just not legal for it to be more. In some states, marinas are exempt from listing ethanol content, so just because there's no label, that doesn't mean there's there is no ethanol — ask the operator. In most areas, E0 is considered a "boutique fuel" and costs more than E10. Finally, if you want to know exactly how much ethanol there is in gas, you can test it yourself. Simple reusable kits are available online that will accurately find the ethanol content.


BoatUS Editors

Contributor, BoatUS Magazine

Award-winning BoatUS Magazine is the official publication of Boat Owners Association of The United States. The magazine provides boating skills, DIY maintenance, safety, news and more from top experts.