Know Your Fuel!

The Quality of Fuel Determines How Well a Marine Engine Will Run

Gasoline quality has gone south. A few years ago, in the interest of squeezing more gallons of gas out of a barrel of crude oil, the process for achieving an 87-octane fuel blend was revised. The result is a pretty nasty concoction. When two-stroke outboard motors burn 87 octane, carbon and other deposits build up in the combustion chamber, in ring grooves, and in and around exhaust ports. Because carbon is abrasive, it causes piston scuff, ring wear, and scored cylinder walls. All this can dramatically shorten outboard motor life.

When premature engine aging first came to light, outboard motor manufacturers weren't sure what the cause was. The breakthrough came when an alert service technician noticed a number of failures on one freshwater lake where only 87 octane was available. Only a few miles down the road at another lake - where only 89 octane was pumped - there were no such failures.

Just so there's no misunderstanding, the carbon buildup problem isn't related to octane, per se. Engine knock, a problem that is related to insufficient octane, isn't the culprit here. The cause of the carbon problem is simply that 87-octane gasoline is a filthy fuel that burns dirty. Eighty-nine octane gasoline, on the other hand, seems to burn much cleaner - to a greater degree than can be accounted for by a mere two-number difference in octane rating. This is because rating numbers tell only part of the story. A fuel's blend is not revealed in its octane rating, and how clean a fuel burns is a function of how it is blended.

Another problem plaguing gas engines is substandard fuel - fuel that is contaminated or of an indeterminate quality. Like low-octane fuel, substandard fuel burns dirty. Most gasoline supplies are delivered through a pipeline. Gasoline of various octanes, diesel fuel, and even liquid fertilizer are all pumped through the same pipe. As a consequence, contamination is common and you can never be absolutely certain your gasoline is pure and pristine or clouded with diesel, junk-octane fuel, or even farm chemicals.

Outboard manufacturers reacted to the filthy fuel problem by introducing a new BIA/NMMA-certified grade of oil (TC W3). They also introduced gasoline additives. Both the oil and the additives prevent the formation of carbon and aggressively work to break down existing deposits.

As of January 1995, the National Marine Manufacturers Association (NMMA) only certifies two-stroke outboard oils meeting TC-W3 requirements. There will no longer be a TC-WII certification. One consequence of this change is that boat owners are paying a bit more for oil because the TC-W3 is more expensive (the actual price you pay will depend on brand name and dealer discounts). On the other hand, TC-W3 definitely delivers more bang for the buck. Not only does it reduce harmful combustion-chamber deposits and carbon buildup, but it also reduces ring wear and fights internal corrosion. As an added bonus, it also lengthens spark plug life and burns cleaner, exhausting less smoke.

If you happen to still have a stock of NMMA-certified TC-WII on hand, you don't have to throw it away. You can burn it in your outboard, but only after treating the fuel supply with an appropriate additive that works the same way that TC-W3 oils do. All of the outboard manufacturers market such additives.

Stern Drives
One myth that has confused the fuel situation, especially among recreational boaters, is that Re-Formulated Gasoline (RFG) is detrimental to marine engines. Rumors are running wild, and misinformed boaters are incorrectly diagnosing engine ailments as the result of RFG. But this new fuel is actually fully compatible with today's marine engines.

RFG came into being with the stroke of the legislative pen when The Federal Clean Air Act of 1990 took effect. Since January of this year, the law requires that gasoline sold in certain urban areas must be RFG. Eventually, all gasoline nationwide must meet this mandate. RFG's admirable purpose is to lessen gasoline's contribution to atmospheric pollution - something it certainly does. Estimates are that RFG reduces carbon monoxide by 13 to 25 percent. Cancer-causing benzene is reduced by 24 percent. Smog-forming hydrocarbons are dropped 15 percent, nitrous oxide by 3 percent, and sulfurides, which cause acid rain, by 11 percent. Beyond its substantial environmental benefits, RFG burns cleaner, producing fewer internal engine deposits

One of the ways RFG reduces pollution is through oxygenation, which simply means adding oxygen molecules to the gasoline blend. Non-RFG gasoline is comprised of hydrogen and carbon, but not oxygen. Oxygenated gasoline converts harmful carbon monoxide (CO) emissions to harmless carbon dioxide (C[O.sub.2]). Gasoline is oxygenated by adding either ether or ethanol, both of which contain oxygen.

RFG is sold in cities with air-quality problems: New York, Los Angeles, Chicago, San Diego, Baltimore, Milwaukee, Houston, Philadelphia and Hartford. Wherever you happen to live, however, keep your eye open for the mandatory label on the gas pump that says, in effect, "Contains oxygenates." You should also ask your marina operator about the availability of RFG.

Unfortunately, RFG does have a downside - its shelf life is significantly shorter than that of previous fuels. RFG's lighter hydrocarbons evaporate more readily, leaving heavier, gummier molecules behind. These heavy molecules gum up fuel filters and carburetor passages. For this reason it's very important to stabilize RFG gasoline if you're going to keep it for more than 90 days.

Also, because ethanol-based RFG (but not ether-based RFG) is more hygroscopic than previous blends, it tends to absorb water more readily. The solution is to top off regularly. Full fuel tanks minimize condensation and water buildup.

If your fuel system does not include a water-separating fuel filter, you should install one. Fuel/water separators work just as well for gasoline as for diesel. A separator will not only pull water out of the gas, but it will also trap dissolved deposits and debris - important because RFG is a powerful fuel-system scrubber. RFG's oxygenates are solvents that dissolve dirt and gum that build up in the fuel tanks. They're so effective that fuel filters tend to clog up sooner with the suspended residue. Once again, the solution is simple: Change fuel filters frequently until RFG has completely cleansed the tank and lines.

RFG should not noticeably affect performance; but ethanol-based RFG contains slightly fewer BTUs per gallon than its predecessor, which translates into a slightly lean fuel-to-air mixture. In a worst-case scenario, an engine might idle rougher. The remedy is to enrich the idle mixture until you find smooth running. Of course, fewer BTUs per gallon will also mean reduced fuel economy, and there's no ready remedy for that unfortunate fact.

Finally, ethanol-based RFG is a bit finicky when compared to ether-based fuel. And you often can't tell which blend you're topping off with, because not all states require pumps to be labeled. But even if you aren't sure what you're burning, remember that preventive measures like filtering and stabilizing are sound practice for every blend. Water has always been a problem in fuel, and it's best to be prepared.