Boating is a big part of enjoying time with friends and family. Whether you are an experienced or novice boater, nothing is more disappointing than a fuel-related mechanical problem that can ruin your entire day. This is especially true given the amount of planning and preparation that can go into a typical day on the water.

With the amount of time a boat spends in the water, there is bound to be some water intrusion into the fuel system. After all, while boat hulls are designed for use on the water, their engines and fuel systems are not. Water in the fuel can lead to a variety of troublesome mechanical issues, as well as actual damage. If you have a hard starting engine, acceleration hesitation, engine sputtering, uneven idle, or poor fuel economy, there is a good chance that you are having a problem with some abnormal concentration of water in your fuel.   The Common Fuel Used in Boats – E10 Before we talk about the damage water can cause in the fuel system and how to prevent it, let’s start off with a discussion of the fuel itself. Most major outboard motor manufacturers approve the use of E10 fuel in their engines. E10, also known as gasohol, is blended with 10% ethanol and 90% gasoline. It is the common fuel found in most gas stations and fuel docks in the United States. Ethanol-free gasoline (E0) exists, however, it is only offered at limited locations around the country. Although E0 is the best option for boats, E10 is still the dominant fuel used in boats due to its widespread availability. E15, on the other hand, is an ethanol-gasoline blend that contains up to 15% ethanol. It may be priced lower than E10, but it is not approved for use in boat engines. E85, also called flex fuel, is a high ethanol-gasoline blend intended for specially designed engines only. It mostly contains 51% to 83% ethanol in the U.S., but the percentage could vary depending on the geographical location.   Why is Ethanol Added to Fuel? Ethanol, also called ethyl alcohol, is a combustible liquid mainly derived from corn, sugar cane, or other cellulose feedstock. Ethanol is added to gasoline to meet the requirement of the U.S. Renewable Fuel Standard. It acts as an “oxygenator” to allow gasoline to burn more efficiently, thereby reducing greenhouse gas emissions. Ethanol also provides a higher octane rating, which helps to prevent engine knocking.   How Does Ethanol Lead to Water in Fuel? The problem with ethanol in fuel is that it is hygroscopic — which means it absorbs water. Therefore, using an ethanol-blended fuel, such as E10, contributes to water absorption in the fuel tank far beyond what would occur with ethanol-free fuel. But how does water get in? The most common way is from build-up of condensation resulting from temperature differences throughout the day. This is especially prevalent during the summer months and in high humidity environments. As warm air inside the fuel tank cools down throughout the night, the moisture in the air condenses into water, forming droplets on the inner wall of the fuel tank. These droplets then accumulate and eventually “sweat” down into the fuel. This process repeats day after day. The more fuel tank surface is exposed, the more droplets can be formed and sweat into the fuel. Once the fuel is saturated with water, ethanol attaches to the water and separates itself from the fuel, leading to a phenomenon known as “phase separation.” The result is two distinct layers in the fuel tank: an upper “gasoline” layer and a lower “ethanol-water” layer.   Problems with Phase Separation Engine damage: The upper gasoline layer will be depleted of ethanol resulting in reduced octane. This makes it less combustible and can cause engine knocking, pinging, or even loss of power. Even worse, if the lower ethanol-water layer is picked up by the fuel pump and gets sent to the engine, it can cause catastrophic engine failure because an engine simply will not run on a mixture of ethanol with water. Corrosion: The lower phase, separated ethanol-water layer will be cloudy and highly corrosive. It can cause rust and corrosion inside the fuel tank and form loose metal oxide particles. These particles can then clog up lines, fuel filters, fuel pumps, or even create damage to your fuel injectors if the particles manage to pass through the fuel filters. Microbial contamination: In boats, fuel often sits in the fuel tank for months during winter season. When your boat is at rest, the stagnant ethanol-water layer creates a perfect breeding ground for bacteria and fungi. This microbial infestation not only produces acids that further promote corrosion, but it also causes sludge and slime build-up inside the fuel tank.   Should I Use a Fuel Treatment to “Reverse Phase Separation” or “Remove Water”? Despite claims from some aftermarket fuel treatment products to “reverse phase separation” or “remove water,” it is technically not recommended. The reason is that these products usually contain emulsifiers or demulsifiers that come with lots of drawbacks. Emulsifiers attempt to keep water in the fuel as a homogenous solution. The thought is that these microscale water particles can then pass through the fuel system and get burned inside the combustion chamber. Although this method may potentially reduce some of the stagnant water from the fuel tank, water is now passing through the fuel filter and water separator, bringing along any slime or sludge, gushing down the injectors as hot steam, causing corrosion, and affecting the spray pattern. Many emulsifiers also contain alcohol meant to dissipate the water — which can lead to additional water absorption. Demulsifiers work by facilitating the separation of water from the fuel so it may then be drained mechanically. This indeed promotes phase separation, which can further lead to stagnant water formation, bacteria growth, and corrosion in the fuel tank if water is not promptly removed. The treated fuel is also not suitable for use due to lower octane levels. In fact, no chemical agent or fuel additive can be added to ethanol-blended gasoline, in a reasonable quantity, to completely prevent phase separation or recombine a phase-separated gasoline. You can minimize water intrusion with good fuel management practices and look for a comprehensive fuel treatment that protects against the harmful effects of water in fuel.   The Best Practice If you experience the symptoms mentioned above and suspect that you are having problems with water in fuel, begin by checking your fuel tank. If there is water present, empty and clean your fuel tank. Fill it up with fresh, high-quality fuel up to 95% capacity. This minimizes air space and moisture contact inside the tank, but still leaves room for fuel to expand. Install a quality fuel/water separator, then add a multi-functional, alcohol-free, emulsifier-free aftermarket fuel treatment – for example, Techron® Protection Plus Marine Fuel System Treatment. Its alcohol-free formulation does not contribute to water absorption. In exhaustive testing, Techron Marine with corrosion inhibitors was proven to provide maximum corrosion protection in both fresh and salt water. To maintain your fuel system in a healthy condition and optimize engine performance throughout the boating season, it is recommended to add Techron Marine with every fill-up. It cleans carbon deposits, dissolves gum and varnish buildup, and helps prevent new deposit formation. If you’re storing the boat for the winter, using Techron Marine can stabilize fuel for up to two years, giving you confidence and peace of mind. Choosing the right fuel treatment can help you mitigate harm from phase separation, corrosion, and fuel degradation. Good fuel management practices — together with regular use of a high-quality aftermarket fuel system cleaner like Techron Marine — will enable you to enjoy worry-free boating year after year.