MOP
05-01-2002, 09:27 PM
WARNING: PROTECT ENGINES FROM DAMAGING FUELS
Modern fuels are causing serious problems with four-cycle fuel systems. Engine operation and lay-up now demands a new approach.
By Jan Mundy
Nowadays, the fuel you're burning is a blend of petroleum, 10% methanol alcohol (a combustion enhancer), detergent and other complex additives. Such reformulated fuel doesn't have a specific makeup; additives are supplied regionally which makes fuel quality suspect depending on where it's purchased.
If you lay-up your outboard or stern drive engine this year the way it's been done for decades draining the gearcase oil, draining the water, fogging, adding stabilizer to a full fuel tank you risk serious problems to your engine's fuel system. During extended storage, some of the alcohol evaporates, but the additives remain. These additives can gum up check valves, hold open the carburetor inlet valve or pressure relief valve on the electric fuel pump (if equipped). Engine manufacturers warn of other damage: seizing of check valves and increase in occurrences of preignition and detonation.
When preparing your engine for extended storage, Mercury Marine now advocates running two-cycle oil through both outboard and stern drive engines. To do this, disconnect the boat's fuel supply. To a portable fuel tank add a 1- gal mixture of fuel, stabilizer and oil (see "Stern Drive Lay-up," Step 2 on page 34) and run this through the idling engine. Detergents and additives will be suspended in the oil and then exhausted when starting the engine after lay-up.
Some engine manufacturers also now recommend draining the fuel tank. Run the engine until the tank is nearly empty. To the fuel remaining in the inboard tank, add an equal amount of fuel stabilizer containing methyl hydrate to absorb the moisture accumulated through condensation eek! . Before relaunching, top up the tanks with fresh fuel and add more stabilizer.
Draining fuel tanks totally contradicts our article "To Empty or Not?" in DIY 1998-#3 issue. To the best of our knowledge, based on discussions with representatives from the American Petroleum Institute and major refinery additive suppliers, there are potential damaging affects from storing fuel tanks empty. All tanks oxidize in the presence of oxygen, whether they're made of metal or plastic, which can leave minute particles floating in the fuel. Besides collecting water through condensation in the bottom of the tank, the internal tank seals will eventually dry out when not immersed in fuel, creating a fuel leak.
According to our sources, water requires equal amounts of methyl chloride to disperse it. An empty 200-gal tank, for example, can potentially collect through condensation 2gal or more of water, thus requiring at least 2gal of stabilizer. But such a high concentration, say the experts, may not dissipate through the fuel system. The result: your engine stalls, fuel-water separating filter fills with water, and you'll probably need to drain the tank.
Conversely, filling fuel tanks full for extended storage also causes fuel problems. The main concern is loss of octane. After a six-month or longer storage period, the octane level apparently decreases to about 85. Low-octane fuels can cause damage to pistons in older engines. Should you opt to store tanks full, Mercury recommends filling tanks with the highest-grade fuel available, preferably 94 octane, and adding a fuel stabilizer. At launch time, add an octane booster, then run the engine until you can top up the tanks with a substantial quantity of high-octane fuel.
Detergents and other additives were added to make engines run more economically and more environment-friendly. Now, some states (i.e. California) are banning reformulated gasoline because exhaust emissions from a tuned engine are considered more hazardous than non-reformulated fuels, but replacement additives may be just as damaging to marine engines. I suspect engine manufacturers will continue to amend engine design and maintenance techniques. We'll keep you posted in upcoming issues but in the meantime, contact the engine manufacturer or your local dealer for maintenance updates.
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© JM Publishing. All rights reserved. No portion of this site may be used without advance written consent.
Modern fuels are causing serious problems with four-cycle fuel systems. Engine operation and lay-up now demands a new approach.
By Jan Mundy
Nowadays, the fuel you're burning is a blend of petroleum, 10% methanol alcohol (a combustion enhancer), detergent and other complex additives. Such reformulated fuel doesn't have a specific makeup; additives are supplied regionally which makes fuel quality suspect depending on where it's purchased.
If you lay-up your outboard or stern drive engine this year the way it's been done for decades draining the gearcase oil, draining the water, fogging, adding stabilizer to a full fuel tank you risk serious problems to your engine's fuel system. During extended storage, some of the alcohol evaporates, but the additives remain. These additives can gum up check valves, hold open the carburetor inlet valve or pressure relief valve on the electric fuel pump (if equipped). Engine manufacturers warn of other damage: seizing of check valves and increase in occurrences of preignition and detonation.
When preparing your engine for extended storage, Mercury Marine now advocates running two-cycle oil through both outboard and stern drive engines. To do this, disconnect the boat's fuel supply. To a portable fuel tank add a 1- gal mixture of fuel, stabilizer and oil (see "Stern Drive Lay-up," Step 2 on page 34) and run this through the idling engine. Detergents and additives will be suspended in the oil and then exhausted when starting the engine after lay-up.
Some engine manufacturers also now recommend draining the fuel tank. Run the engine until the tank is nearly empty. To the fuel remaining in the inboard tank, add an equal amount of fuel stabilizer containing methyl hydrate to absorb the moisture accumulated through condensation eek! . Before relaunching, top up the tanks with fresh fuel and add more stabilizer.
Draining fuel tanks totally contradicts our article "To Empty or Not?" in DIY 1998-#3 issue. To the best of our knowledge, based on discussions with representatives from the American Petroleum Institute and major refinery additive suppliers, there are potential damaging affects from storing fuel tanks empty. All tanks oxidize in the presence of oxygen, whether they're made of metal or plastic, which can leave minute particles floating in the fuel. Besides collecting water through condensation in the bottom of the tank, the internal tank seals will eventually dry out when not immersed in fuel, creating a fuel leak.
According to our sources, water requires equal amounts of methyl chloride to disperse it. An empty 200-gal tank, for example, can potentially collect through condensation 2gal or more of water, thus requiring at least 2gal of stabilizer. But such a high concentration, say the experts, may not dissipate through the fuel system. The result: your engine stalls, fuel-water separating filter fills with water, and you'll probably need to drain the tank.
Conversely, filling fuel tanks full for extended storage also causes fuel problems. The main concern is loss of octane. After a six-month or longer storage period, the octane level apparently decreases to about 85. Low-octane fuels can cause damage to pistons in older engines. Should you opt to store tanks full, Mercury recommends filling tanks with the highest-grade fuel available, preferably 94 octane, and adding a fuel stabilizer. At launch time, add an octane booster, then run the engine until you can top up the tanks with a substantial quantity of high-octane fuel.
Detergents and other additives were added to make engines run more economically and more environment-friendly. Now, some states (i.e. California) are banning reformulated gasoline because exhaust emissions from a tuned engine are considered more hazardous than non-reformulated fuels, but replacement additives may be just as damaging to marine engines. I suspect engine manufacturers will continue to amend engine design and maintenance techniques. We'll keep you posted in upcoming issues but in the meantime, contact the engine manufacturer or your local dealer for maintenance updates.
BACK / HOME / SEND PAGE TO A FRIEND
Inquiries or Comments? Send them to our editor at info@diy-boat.com
© JM Publishing. All rights reserved. No portion of this site may be used without advance written consent.