Marine boat owners invest a great deal of time and money in their watercrafts, and they expect the fuels they put in them to perform optimally every time with a minimum of problems.
Yet experienced boat owners know certain kinds of fuel-related problems do exist and come with the territory - they may even be viewed as inevitable. Some users simply put up with these issues while other watercraft owners fight back through the treating of their marine fuel in the hopes that these problems will go away or never appear.
Marine fuels, whether they are ethanol-blended gasoline or marine diesel fuel, have the same kind of issues that their on-road fuel equivalents have. Yet the unique humid nature of the marine environment means that some of the problems are amplified.
The biggest difference in environment is that the humid marine environment is a perfect setting for water to condense in vented fuel tanks, where it collects and sinks to the bottom of the tank.
In diesel fuel, this water buildup promotes oxidation and fuel breakdown. Water in any kind of petroleum fuel - gas or diesel - contributes some of the building blocks needed for hydrolysis and oxidation reaction to occur in the fuel. These types of reactions cause a chain reaction in the fuel, breaking apart stable fuel molecules, darkening the fuel and reducing its quality.
Since diesel fuels tend to be stored longer (if your marina stores diesel fuel for use by multiple boats), bacterial and fungal growth is always a possibility when water is present. Once bacteria and other microbes establish a foothold, they are impossible to get rid of without a biocide, and lead to further diesel quality breakdown, corrosion of tanks, deposit buildup and nasty filter plugging problems.
Ethanol-gasoline fuels don't spend as much time being stored as diesel fuels do, but they have their own serious problems with water buildup. This is because ethanol chemically attracts water out of the surrounding air - this ia bad enough problem for cars and trucks, but the marine air makes it even worse. Water buildup in ethanol fuels promotes phase separation, where the water will pull the ethanol out of the blend and mix with it on the bottom of the tank, leaving a poor combusting, low-octane gasoline layer up top. If this gets sucked up into your engine, it can, at the least, result in lean fuel mixtures, rough running and poor performance by the boat, and at worst, serious engine damage through burnt valves can results.
Ethanol blends also do a serious number on rubber and plastic fuel system parts and tanks. The ethanol in the blend has a corrosive effect, eating away and dissolving these parts over time. A leaky fuel tank or gas line due to ethanol solvency is a serious fire hazard and can leave you stranded on the water. What's more, the dissolved plastics, rubber parts and resign lead to serious deposit buildup and filter-plugging.
Consumers on land have become keenly aware of these solvent action when their small equipment pieces all stopped working because the ethanol left in their tanks destroyed the equipment's fuel lines.Boats have the same problems. And both of these kinds of equipment are more prone to ethanol damage than cars and trucks because boats are more likely to be older and made from the types of materials that aren't fully resistant to ethanol. Most cars and trucks made after, say, 2007, have this problem solved.
Speaking of deposits, many boats do a lot of idling and this means greater chance of deposits building up in engines using either diesel or ethanol. Whether injector or valve or combustion chamber deposits, they all have ill-effects on boat fuel mileage, performance and the black exhaust smoke so commonly seen especially in diesel marine engines.