A General Discussion on E10 Fuels

Memo to: Dare Marina Customers

Subject: Fuel Problems and Recommendations for Good Boating

Attachment A: MEMORANDUM, SUBJECT: Water Phase Separation in Oxygenated Gasoline; Corrected version of Kevin Krause memo; FROM: David Korotney, Chemical Engineer

Dear Customers of Dare Marina and Yacht Sales

I am sure most of you are aware that the introduction of E10 gasoline fuel has resulted in a decrease in fuel stability in the marine environment. This has led to a number of unexpected engine shutdowns, and moderate to expensive engine repairs. We in the Dare Marina Service Department continue to address engine issues resulting from fuel breakdown, and want to keep you informed of the more serious issues as we understand them, and suggest actions that should help minimize these issues from interfering with an enjoyable boating experience.

The most significant fuel problems and actions to avoid or remediate those problems are listed as follows:

Another E10 problem. We recently had a boat in for brokerage (not fueled here) that badly failed the leakdown test, indicating stuck rings (compression was good). On examination with a borescope, it was clear the inside of the cylinders and power head are badly carbonized. Presumably the some of the piston rings are stuck. On discussion with the engine manufacturer, the tech rep said that one of the not well understood attributes of E10 fuels is that, even if one uses high test fuels, when the ethanol evaporates from sitting in the hot sun in a vented tank the octane may well be satisfactory but the ethanol’s oxidizing properties are lost and the gas burn is dirty. This potentially results in carbon buildup. The engines in question (two engines with essentially identical properties) had about 650 hours of operation each. This aspect of E10 is another problem to add to the list. We contacted our fuel brander, ValvTect, and asked them to address this issue and whether the ValvTect additive . Do the stabilizing properties of ValvTect resolve this issue? Does it somehow keep the Ethanol from evaporating? The ValvTect representative responded as follows, “When ethanol and other light ends evaporate from the fuel, the octane of the fuel will decrease by 2-3 octane numbers. The remainder of the gasoline is heavier and can burn to produce a higher level of deposits than the mother E10. Additives can’t stop the evaporation of ethanol. Additives can stop the gum formation on critical surfaces.”

Mixing Ethanol and MBTE enhanced gasoline – When ethanol and MBTE gasoline are mixed together and allowed to sit for an extended period, there is a chemical reaction that forms small beads of yellow gum. This reaction is most apparent at elevated temperatures, such as occur in the fuel system of fuel injected engines. This gum can foul injectors or jets, and can result in an expensive disassembly and repair. Also, since the gum beads form after the fuel is beyond the main fuel filters, it can plug up the filter inside the VST and result in a lean run condition – this can do serious engine damage. In situations where a transition between these fuels is necessary, we suggest that the engine(s) be run to reduce the quantity of fuel in the fuel tank to a minimum safe level. If the engine(s) are fuel injected, the remaining fuel should be pumped out of the tank and then the alternate fuel be introduced. . An in-line 10 micron fuel filter should help mitigate problems if gum forms in the main fuel tanks – gum formation in the main tank is not a major problem but there are many other reasons for this filter Cleaning effect of Ethanol enhanced gasoline on old fuel tanks – Ethanol is an excellent cleaning agent, and when introduced to fuel systems and tanks that have some years of prior use “scrubs” oxidation, varnish and residue off wetted surfaces including the walls of the tank. While in some cases this may be a “good” cleaning, it is important that the materials so removed not find their way into the engine itself. Corrosion of fuel sender components has also been observed when tanks are left empty. Where MBTE fuels are used, these components are protected to a degree by varnish that forms on the surface. However ethanol enhanced fuels do not deposit these varnishes. Again, a 10 micron fuel/water separator between the fuel tank and the engine’s fuel system should be considered a must. During the period immediately following the introduction of Ethanol enhanced fuel, this filter should be checked often to assure that it is not becoming clogged and starving the engine(s) for fuel.

Aluminum and fiberglass fuel tanks are not recommended for ethanol enhanced fuels. Fiberglass tanks tend to dissolve in ethanol and the aluminum will corrode over time with ethanol fuels. This is especially true if the ethanol used in the blend contains a high level of sulfates. The sulfates combine with the water molecules absorbed by the E10 fuel and form sulfuric or sulfurous acid, which aggressively destroys the protective film on aluminum surfaces. In addition to ultimately developing leaks, the products of this damage will clog filters and can break through the paper filter element. On fuel injected engines, this can result in shorting the armature of the high pressure fuel pump and clog the injectors.

Effect on Soft Elements Incompatibility of soft elements (hoses, diaphragms, plastic parts) with modern fuels – Older engines and craft may have components containing rubber and plastic compositions that have not been reformulated for ethanol compatibility. Owners of older equipment should check visible components to confirm that suppleness remains adequate and that cracks do no appear on the surface when the item is flexed. For some particularly important components such as fuel pump diaphragms that are not readily visible, disassembly to check flexibility and leakage is prudent (it may be cheaper to simply replace the pump). Even the newer formulations have a shorter life than generally experienced before E10.

Octane Stability – Reliable sources indicate that the stability of today’s fuels does not correspond to our experience from years ago, and that the refiner’s specifications for the fuel are only valid for about 40 days after the fuel is placed in a vented environment. That is not to say that the fuel is “bad” at this point, but presumably some of its properties, particularly octane, are reduced. Since the ethanol in E10 accounts for about 3 points of octane, 87 octane fuel could be reduced to 84 octane, which will seriously damage most of today’s marine engines. This problem is exacerbated in fuel tanks directly exposed to the sun.


Phase Separation – Another long term problem with the new ethanol enhanced fuels is the propensity of the ethanol to absorb water and, in the extreme, to “phase separate” from the petroleum content of the fuel. Most (not all) of the serious fuel problems we have seen to date in the Service Department are a result of phase separation. As noted in Attachment A, not only does Ethanol absorb water from the atmosphere, but when the percentage of water exceeds between 0.3% and 0.5% (depending on temperature), the ethanol and water mixture separates from the petroleum (this means that when approximately 2.3 to 3.8 teaspoons of water are dissolved in a gallon of the fuel, the ethanol/water will begin to phase separate). This mixture is heavier than the petroleum content and will tend to migrate to the bottom of the fuel tank. In addition to generally shutting down the engine when the ethanol/water reaches the injectors or carburetor, ethanol/water is electrically conductive and corrosive. If allowed to sit for an extended period in an aluminum fuel tank, carburetor, or injector system serious damage can result. Attachment A states that generally the amount of absorption from the atmosphere is not sufficient to cause separation over reasonable (a few months) of storage in a vented tank. The amount (percent) of water absorbed in this manner is a function of the free surface of the tank, the quantity of fuel below the fuel surface, and time. Whatever the case, absorbed water adds to any other water that may be introduced into the fuel from other sources. In addition to the potential introduction of the separated mixture into the engine, the separation of ethanol from the fuel also lowers the octane level of the fuel, impacting the combustion within the engine. Best practices for avoiding problems from phase separation include a good (10 micron) in-line fuel/water separator, maintaining a ¾ full fuel tank when the boat is in storage (does not change the free surface but provides a larger sink for the water absorbed), and removing any source of direct entry of water into the fuel tank. In this latter regard, most fuel fill ports are located on a more or less horizontal surface. These fuel fill ports are sealed from moisture with an o-ring. We suggest you examine the integrity of this seal on a regular basis (both o-ring and seating surfaces), and assure that ropes, add-on devices, etc., cannot form a dam to cause standing water over the fuel port. After fueling, assuring that the fitting is screwed tightly in place is critical. Another potential entry point for water is the tank vent. Good practice in this case is to assure that the vent line rises from the point where it penetrates the side of the hull before dropping to the vent fixture on the tank itself. The vent should also be protected from entry of rain or spray. A good practice is to use a premium grade of gasoline, so that if some octane is lost, the octane doesn’t drop below 87.

Handling of a fouled fuel tank: While prevention is certainly the preferred solution, sometimes the fuel in a boat tank becomes compromised and needs to be corrected. There are three approaches said to be available. One is to introduce an additive claimed to reform the fuel. Dare Marina is not in a position to recommend this as a general solution and it seems generally accepted that once separation has occurred the fuel cannot be restored by additives alone. We also caution that some of the products contain ethanol – almost all manufacturers warn that ethanol content in excess of 10% voids their warranty. A second approach is to pump the gasoline from the tank and clean the tank. This is generally successful but requires that the gasoline removed be properly disposed – this is not cheap. A third approach is to polish and reconstitute the fuel. We no longer recommend this solution. At this time Engine Manufacturers have not addressed use of polishing and reconstitution and it is not clear what effect using polished and reconstituted fuels may have on manufacturer warranties. It is almost universally true that fuel related issues are outside the warranty of the engine manufacturer, and we have experienced almost new engines that have needed extensive repair that was not covered by the warranty.

Good winterization practice: When you lay your boat up for the winter (or any other extended period), good winterization practice will help to assure that you can return your boat to service in the spring with a minimum of difficulty. Among other “good practices,” storing the boat with the fuel tank near but below 85 % full is recommended (providing room for expansion on hot days) . Dare Marina stands ready to provide winterization service using the latest best practices in the industry.

Careful fuel practices by the boat owner are the best way to avoid problems: Some of the concepts below may be redundant to earlier comments, but are gathered here for your convenience.
1. Check the seal on your fuel cap. The o-ring/gasket should be in good condition and seal tightly against the seat
2. Make sure the vent has a loop to prevent water from running down hill into the tank, and is oriented to reject rain and spray.
3. Use a high quality fuel bought from a reliable supplier and a tested fuel stabilizer. Original octane should be not less than 89. We at Dare Marina are selling ValvTect Marine fuels that are blended by the supplier to assure the correct mixture. The fuel tank is tested periodically to confirm that it is water free.
4. Use your boat. Long term storage of unused fuel in vented boat tanks is probably the single greatest cause of fuel problems.
5. If you have a fuel related failure, pump your tank and fill with fresh fuel. Adding fresh fuel to contaminated fuel has been compared to adding fresh milk to sour milk – all that results is a greater quantity of sour milk

For more discussion, read Marine Surveyer Earl Joyner’s article on E10 in the marine environment by clicking here.

Attachment A

SUBJECT: Water Phase Separation in Oxygenated Gasoline
– Corrected version of Kevin Krause memo
FROM: David Korotney, Chemical Engineer
Fuels Studies and Standards Branch
TO: Susan Willis, Manager
Fuels Studies and Standards Group

On May 26, 1995, Kevin Krause finalized a memorandum describing the conditions under which water phase separation will occur in oxygenated gasolines. Recently, several errors were discovered in that memorandum. I have made the necessary corrections, and now resubmit the complete text of Kevin’s memo for your review and approval.

With the introduction of oxygenated gasoline came the concern of water phase separation. Water in gasoline can have different effects on an engine, depending on whether it is in solution or a separate phase, and depending on the type of engine being used. While separate water phases in a fuel can be damaging to an engine, small amounts of water in solution with gasoline should have no adverse effects on engine components. If precautions to prevent water from entering the fuel system are taken, water phase separation will likely not occur.

Oxygenated fuels usually contain either ethanol or methyltertiary-butyl-ether (MTBE). Other possible oxygenates include ethyl-tertiary-butyl-ether (ETBE), tertiary-amyl-methyl-ether (TAME), and tertiary-butyl-alcohol (TBA). Chemically, ethanol and MTBE behave differently. Ethanol, for example, will readily
dissolve water, and is considered infinitely soluble in water. MTBE, on the other hand, has little affinity for water, and can only be dissolved in water to a content of 4.3 volume percent (at room temperature). Therefore, ethanol/gasoline blends can dissolve much more water than conventional gasoline, whereas gasoline/MTBE blends act very much like conventional gasoline when in the presence of water.
Since ethanol and water readily dissolve in each other, when ethanol is used as an additive in gasoline, water will actually dissolve in the blended fuel to a much greater extent than in conventional gasoline. When the water reaches the maximum amount that the gasoline blend can dissolve, any additional water will separate from the gasoline. The amount of water required (in percent of the total volume) for this phase separation to take place varies with temperature, as shown in Figure 1. As an example, at 60 degrees F, water can be absorbed by a blend of 90% gasoline and 10% ethanol up to a content of 0.5 volume percent before it will phase separate. This means that approximately 3.8 teaspoons of water can be dissolved per gallon of the fuel before the water will begin to phase separate.


Since MTBE has much less affinity for water than does ethanol, however, phase separation for MTBE/gasoline blends occurs with only a small amount of water, as shown in Figure 2. A blend of 85% gasoline and 15% MTBE can hold only 0.5 teaspoons at 60 degrees F per gallon before the water will phase separate. For comparison, one gallon of 100% gasoline can dissolve only 0.15 teaspoons water at the same temperature. These figures are far below the 3.8 teaspoons which will cause phase separation in the 90/10 ethanol blend. Water can enter gasoline engines in two ways: in solution with the fuel or as a separate phase from the gasoline. Water in solution operates as no more than an inert diluent in the combustion process. Since water is a natural product of combustion, any water in solution is removed with the product water in the exhaust system. The only effect water in solution with gasoline can have on an engine is decreased fuel economy. For example, assuming a high water concentration of 0.5 volume percent, one would see a 0.5 percent decrease in fuel economy. This fuel economy decrease is too low for an engine operator to notice, since many other factors (such as ambient temperature changes, wind and road conditions, etc.) affect fuel economy to a much larger extent.

Water as a separate phase, however, can have differing effects on gasoline engines, depending on whether the engine is two-stroke (generally, smaller engines) or four-stroke (generally automobile engines). In the case of conventional and MTBE blended gasolines, when a water phase forms, it will drop to the bottom of the fuel tank, and can therefore be drawn into the engine by the fuel pump. Therefore, large amounts of water will prevent the engine from running, but no engine damage will result.

Phase separation in ethanol-blended gasoline, however, can be more damaging than in MTBE blends and straight gasoline. When phase separation occurs in an ethanol blended gasoline, the water will actually begin to remove the ethanol from the gasoline. Therefore, the second phase which can occur in ethanol blends contains both ethanol and water, as opposed to just water in MTBE blends and conventional gasoline. In the case of two-stroke engines, this water-ethanol phase will compete with the blended oil for bonding to the metal engine parts. Therefore, the engine will not have enough lubrication, and engine damage may result. In the case of four-stroke engines, the water-ethanol phase may combust in the engine. This combustion can be damaging to the engine because the water ethanol phase creates a leaner combustion mixture (i.e. air to fuel ratio is higher than ideal). Leaner mixtures tend to combust at higher temperatures, and can damage engines, particularly those without sensors to calibrate air to fuel ratios.
Phase separation, however, generally only occurs when liquid water (as opposed to water vapor) is introduced to the fuel system. If tank vents are left open, either in the engine being operated, or at a fuel distribution station, water can enter the fuel system in the form of rain (or spillage, etc.) or through the air in the form of moisture. Also, since conventional gasoline absorbs very little water, there is often a layer of water present at the bottom of a filling station tank normally used to store conventional gasoline (water is more dense than gasoline, and will therefore sink to the bottom). Before an oxygenated gasoline is added to such a storage tank for the first time (particularly ethanol-blended fuels), this water must be purged from the tank to prevent the water from removing any ethanol from the fuel. Since the solubility of water in both gasoline and air decreases with a decrease in temperature, water can enter a fuel system through condensation when the atmospheric temperature changes. For example, assume a tank containing conventional gasoline contains only one gallon of fuel. Assume also that it is closed while the outside temperature is 100 degrees F with a relative humidity of 100 percent. If this tank is left sealed and the temperature drops to 40 degrees F, water will likely condense on the inside of the tank, and dissolve in the fuel. In order for enough water to condense from the air to cause gasoline-water phase separation, however, there must be approximately 200 gallons of air per gallon of fuel over this temperature drop (100 to 40 degrees). Since oxygenated fuels can hold even more water than conventional gasoline, it is even more unlikely that enough water will condense from the air to cause gasoline-water phase separation.

Another way water can enter gasoline is through absorption from the air. Water, in the form of water vapor, can dissolve in gasoline. The more humid the air, the faster the water vapor will dissolve in the gasoline. Due to chemical equilibrium, however, assuming a constant temperature, phase separation will never occur if the only source of water is from the air. Only enough water to saturate the fuel can enter the system, and no more. Water vapor, however, dissolves in gasoline very slowly, even at very high humidity. For example, at a constant temperature of 100 degrees F and relative humidity of 100%, it would take well over 200 days to saturate one gallon of gasoline in an open gasoline can (assuming the only source of water is water vapor from the air). Water absorption from the air is far slower at lower temperatures and humidities. (At a temperature of 70 degrees and relative humidity of 70%, it would take over two years to saturate one gallon of conventional gasoline in the same gasoline can.) Again, oxygenated gasolines can hold more water than conventional gasoline, and would therefore take much longer to saturate with water.

Water phase separation in any gasoline is most likely to occur when liquid water comes in contact with the fuel. (Water in the form of moisture in the air will generally not cause phase separation.) Water which is in solution with gasoline is not a problem in any engine, but as a separate phase it can prevent an engine from running or even cause damage. Since oxygenated gasolines, however, can hold more water than conventional gasoline, phase separation is less likely to occur with oxygenates present. For any gasoline, simple precautions to prevent phase separation from occuring should be taken. First of all, gasoline should not be stored for long periods of time, especially during seasonal changes which usually have large temperature changes associated with them. (For both oxygenated and conventional gasolines, gumming can also occur which is detrimental to any engine.) If it is unavoidable to store gasoline for a long period of time, one should be sure that the tank if full to prevent condensation of water from the air, and the addition of a fuel stabilizer should be considered. Lastly, care should be taken not to allow water into the fuel system while filling fuel tanks or operating the engine — in the form of rain or a splash, for example.

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