Fuel Before Winter Layup

[seasick]

I don't see how you would not get water with non E gas since the condensation is water and that would fall to the bottom of the tank. Likewise
in the he ethanol gas case, the gas will absorb about 1/2% water by volume and then if won't absorb any more from the water vapor. The condensation effect would still be the same though so if a lot a water condensed, it will fall to the bottom. In those two cases, the ethanol tank would have less water on the bottom.
I am aware that when E10 was introduced and in my state, mandated, we did see a lot of fuel system issues but hose were mostly due to deterioration of fuel lines and the dissolving of fuel system gunk by the alcohol. Over time, a few seasons, those issues were no more prevalent than they had been historically before E10.

We, the boating community, really need more scientific controlled studies on the issue especially with the possible mandate for E15.

 

[usmm1234]

I don't see how you would not get water with non E gas since the condensation is water and that would fall to the bottom of the tank. Likewise
in the he ethanol gas case, the gas will absorb about 1/2% water by volume and then if won't absorb any more from the water vapor. The condensation effect would still be the same though so if a lot a water condensed, it will fall to the bottom. In those two cases, the ethanol tank would have less water on the bottom.
I am aware that when E10 was introduced and in my state, mandated, we did see a lot of fuel system issues but hose were mostly due to deterioration of fuel lines and the dissolving of fuel system gunk by the alcohol. Over time, a few seasons, those issues were no more prevalent than they had been historically before E10.

We, the boating community, really need more scientific controlled studies on the issue especially with the possible mandate for E15.

I base my statements on actual results in the field. I ran a very large outboard boat dealership in SC with a very large customer base. Our state offers non ethanol for Marine and small engines. Our Walmart Super Store has it on all 8 pumps. All our Marinas are non ethanol. My direct experience with hundreds of boats is that if you use non ethanol gas, you will have less water in your tank and your carb components and or fuel injectors will not corrode from moisture.
My father was a Cornell educated chemical engineer and worked for Exxon Research and Engineering for 40 years. He never put ethanol gas in his outboard powered Grady White.
I’ve noticed in my many years in the Marine Industry, that most people supporting the use of ethanol live where non ethanol gas is not available or they are corn farmers LOL.

 

[trapper]

Holy Sh... It has come very clear to me now , why they call you "Doc" Stressor. That was a well explained tutorial !!!! and one that even this ageing mind could grasp. Thanks Doc!

 

[Doc Stressor]

Explaining why more water accumulates in a tank partially filled with E10 vs pure gasoline is a little more difficult. I'll give it a try.

The import factors are diffusion and partial pressure. In a gas (or liquid), molecules move from areas of higher concentration to lower concentration. That's diffusion. The partial pressure of a gas is the amount of pressure exhibited by that particular gas (in this case water vapor) in a mixed gas phase such as air. Partial pressure determines the movement of gases, which tend to equalize their pressure by diffusion between 2 connected regions.

In a tank partially filled with E10, the continuous absorption of water vapor by the fuel phase lowers the partial pressure of the water vapor in the air phase. So water vapor keeps diffusing in through the vent until you have phase separation of the ethanol and gas. With pure gasoline, the partial pressure of water vapor only occurs if water condenses on the surface of the inside of the tank. Otherwise, it is in equilibrium with the air outside of the tank and there is no net inflow of water vapor.

If some water does accumulate in a tank of pure gas, it drops to the bottom of the tank and does little harm. Anything that gets sucked up into the fuel siphon will be trapped by the fuel filter/water separator(s) where it can easily be drained. With E10, you get a sudden phase separation once the water content exceeds 0.3-0.4% of the fuel volume. All of sudden you have a lower layer of separated water and ethanol that is about 8% of the fuel volume. This gets sucked up by the siphon and fills the fuel filters either stopping the flow or entering the VST (depending on the filter media). Plus, the remaining fuel is only about 83 octane, since ethanol is used as an octane enhancer. This can cause engine damage if you just remove the ethanol/water phase.

By keeping a tank of E10 almost full, you minimize the volume of the gas phase, which reduces the amount of water vapor that can be present in the tank. You also minimize the amount of surface area where condensation can take place.

 

[seasick]

OK. From now on my alcohol goes in my mouth!

 

[seasick]

Doc,
Can't the water vapor in the air in the tank condense on both the tank sides AND the gasoline liquid surface kind of like fog on the water? If so, It seems to me that a gas tank which is usually longer and wider than it is deep contributes a good portion of the exposed surface area. That includes the exposed insides of the tank walls and the underside of the top. For the most part, the underside of the top is fixed, the surface of the liquid is basically fixed(excluding an empty tank). The variable is the exposed side area which will change based on the gas level. The relative change of exposed total area is not that large. This is why I don't see a huge correlation between a full tank and a not full at all tank.

I understand the concept of the tank 'breathing' via the vent line. As the air in the tank warms up, pressure is released through the vent. Likewise when the internal air cools, outside air is sucked in. That may or may not contribute to added water content in the air though. That depends on the relative humidity of the outside air.
I can see that with E10, its hygroscopic properties can account for water absorption that wouldn't normally occur with non ethanol gas. What I don't know is if the rate of absorption is affected by the gas's current water concentration. In other words, does 'wet' ethanol fuel absorb moisture at a different rate than 'dry' ethanol fuel all other factors being equal?

So we have too processes going on: possible condensation and the absorption of water vapor due to the hygroscopic property of ethanol gas. Is the second factor the more important?

Sorry for my rambling but it's cold and very windy and no boat work will get done today and I am a tad bored.

 

[Doc Stressor]

It's true that water vapor can condense on the top surface of the tank even if it is almost completely filled. Filling the tank just reduces the amount of surface for condensation to occur.

Your point about air being forced out and in through the vent as temperature changes is probably the biggest reason to keep the tank nearly full. The smaller the volume of air above the tank, the less room for water vapor.

I don't know for sure if nearly saturated E10 is more or less hygroscopic than dry E10. In theory, they should be the same. Water itself is hygroscopic. However, in an open system, the rate of evaporation counteracts this effect. Liquids are hygroscopic if they can form hydrogen bonds with water. Ethanol does this readily. Gasoline is hydrophobic since it cannot H bond with water. Ethanol is soluble in gasoline because of hydrophobic interactions between the alcohol and some of the hydrocarbon components of gasoline. Once there has been enough water absorbed, the attraction between the water and ethanol molecules exceeds the force of the hydrophobic attractions and you have phase separation.

 

[seasick]

Good info. Kind of brings me back to organic chemistry or was it physical chemistry? That was some time ago.

 

[Doc Stressor]

Back in the summer of 1969, I missed going to Woodstock because I was taking all 3 semesters of Calculus and Linear Algebra so that I could take Physical Chemistry in the Fall. I think of that every time I hear the words Physical Chemistry.

 

[usmm1234]

Explaining why more water accumulates in a tank partially filled with E10 vs pure gasoline is a little more difficult. I'll give it a try.

The import factors are diffusion and partial pressure. In a gas (or liquid), molecules move from areas of higher concentration to lower concentration. That's diffusion. The partial pressure of a gas is the amount of pressure exhibited by that particular gas (in this case water vapor) in a mixed gas phase such as air. Partial pressure determines the movement of gases, which tend to equalize their pressure by diffusion between 2 connected regions.

In a tank partially filled with E10, the continuous absorption of water vapor by the fuel phase lowers the partial pressure of the water vapor in the air phase. So water vapor keeps diffusing in through the vent until you have phase separation of the ethanol and gas. With pure gasoline, the partial pressure of water vapor only occurs if water condenses on the surface of the inside of the tank. Otherwise, it is in equilibrium with the air outside of the tank and there is no net inflow of water vapor.

If some water does accumulate in a tank of pure gas, it drops to the bottom of the tank and does little harm. Anything that gets sucked up into the fuel siphon will be trapped by the fuel filter/water separator(s) where it can easily be drained. With E10, you get a sudden phase separation once the water content exceeds 0.3-0.4% of the fuel volume. All of sudden you have a lower layer of separated water and ethanol that is about 8% of the fuel volume. This gets sucked up by the siphon and fills the fuel filters either stopping the flow or entering the VST (depending on the filter media). Plus, the remaining fuel is only about 83 octane, since ethanol is used as an octane enhancer. This can cause engine damage if you just remove the ethanol/water phase.

By keeping a tank of E10 almost full, you minimize the volume of the gas phase, which reduces the amount of water vapor that can be present in the tank. You also minimize the amount of surface area where condensation can take place.

That’s what I meant, but I just don’t have the education to say it! I went to FL Keys Community College in the 70’s if that gives you a clue. But I did stay a Holliday Inn last night.

 

[seasick]

By the way, at the moment I am treating my stomach contents with an alcohol based stabilizer, the red stuff.

 

[Doc Stressor]

I'm going to be doing some alcohol treatment myself in a few minutes.

 

[wrxhoon]

By the way, at the moment I am treating my stomach contents with an alcohol based stabilizer, the red stuff.

That's what I use alcohol for as well, never in my fuel tank in the boat or car for that matter.
I think you guys should use your boats more often don't put E10 in your tanks and you won't have any problems .
Don't forget we have aluminum tanks in our Grady's and the stuff is very corrosive.

 

[seasick]

Good news is that my tank is poly. Bad news is that non ethanol gas is not an option in my area.

 

[Doc Stressor]

Non-ethanol fuel isn't available in most states in the US. Each state has to apply for a waiver. Midwestern states that produce a lot of ethanol are never going to ask for waivers. There are also regulations that require a certain level of renewably sourced fuel in the overall gasoline supply stream.

Most of the problems with E10 in boats have been worked out after the first few years. By now, all of the varnish on the inside of tanks and in the fuel system has already been removed by running E10. Non-compatible hoses and tanks have been replaced. The corrosion problem has largely been solved by regulations that have reduced the allowable sulfur content in E10. The only remaining issues are moisture absorption and more rapid oxidation. These can be addressed with marine fuel additives and by keeping the tank full.

A lot of boaters, myself included, pay the extra $$ for non-ethanol fuel where it is available just to be extra safe. But if I was a guide and going through a tank of fuel every week, I would be running cheaper E10.

 

[usmm1234]

Non-ethanol fuel isn't available in most states in the US. Each state has to apply for a waiver. Midwestern states that produce a lot of ethanol are never going to ask for waivers. There are also regulations that require a certain level of renewably sourced fuel in the overall gasoline supply stream.

Most of the problems with E10 in boats have been worked out after the first few years. By now, all of the varnish on the inside of tanks and in the fuel system has already been removed by running E10. Non-compatible hoses and tanks have been replaced. The corrosion problem has largely been solved by regulations that have reduced the allowable sulfur content in E10. The only remaining issues are moisture absorption and more rapid oxidation. These can be addressed with marine fuel additives and by keeping the tank full.

A lot of boaters, myself included, pay the extra $$ for non-ethanol fuel where it is available just to be extra safe. But if I was a guide and going through a tank of fuel every week, I would be running cheaper E10.

Use lots of fuel additives. Fuel injected outboards are still experiencing corroded and damaged injectors when left to sit for long periods of time. My son ruined the carb on his 3 year old gas generator at his house with modern ethanol fuel. He left fuel in the float bowl. I told him to use Stabil and drain the bowl. There’s a handy little screw and rubber hose already on the bottom of the bowl.

 

[Willy-C]

For the last 10 years I’ve been using stabil and filling the 60 gal boat tank, then in spring I have a 12vdc automotive transfer pump and fill up my 2 road vehicles. That way nothing gets wasted and the boat gets fresh fuel in spring when I need it.

 

[Zebulon]

This............... http://www.valvtect.com/marinefuelgasoline.asp

 

[usmm1234]

Pure-Fuel.gov will guide you too non ethanol all over the country. I’ve traveled by boat from Annapolis MD to The Texas coast and never had trouble finding marina fuel docks with non ethanol. All the Marine gas in the Bahamas is ethanol free.

 

[Doc Stressor]

You should drain carburetor bowls and VSTs during prolonged storage. Since they are open to air, the fuel will eventually evaporate leaving varnish on the dry surfaces.

Some anti-corrosion additives work better than others. Since the industry won't allow testing by independent labs, we have to rely on experience and word of mouth recommendations.

Fuel injectors seem to go out of spec pretty often when boats are not run regularly. It's just the nature of small orifices.