Boat Storage - Full Gas Tank vs Less Than Full

[chpthril]

This has been bugging me for a long time. The octane vs. stale fuel thing just didn't "feel" right to me. Today I finally had a chance to research it a bit more.

The RON rating (commonly but, strictly speaking, erroneously referred to as "octane") refers to the fuel's tendency to burn in a controlled manner, as opposed to exploding. Basically it's a measurement of flame wall propagation speed. As pressures increase, the likelihood of detonation increases but the effect can be offset by additives which increase the RON rating.

The RON rating is entirely separate from the fuel's energy content. Therefore, winterizing with a full tank of higher-RON-rating fuel does NOT mean you're "halfway there" with respect to stale fuel. The fuel's energy content degrades entirely separate from its RON rating.

One rating (RON) has to do with flame wall propagation. The other rating (heat content) has to do with available chemical energy. "Stale" fuel is slang for a degradation of the latter. A higher RON ("octane") rating does not indicate less energy content.

Hope this helps!

Fuels volatility is controlled by the ratio of Heptane to Octane. Volatility is the resistance to, or the point at which fuel ignites. That's why higher octane is recommended for higher compression engines. At the end of the day, 87 has the same BTU's as 93. Basically, once ignited, they deliver the same amount of energy.

Stale, spoiled, degraded, old, etc, fuel is harder (takes more heat) to ignite and burns slower (flame propagation across the combustion chamber) and has less BTU's then fresh. From a refining standpoint, it has the same number of octane molecules. So if you bought 87, it's still 87.

Higher then what is required octane fuel takes more energy to ignite, same as spoiled fuel, and will still spoil at the same rate as lower, like 87, octane fuel. so if you fill the last tank of the season with a fuel that will still be just as spoiled come spring, takes more to ignite, and costs more, what was gained?

Many gas companies advertise that they add special additives to their "Premium" fuel, that some how makes it cleaner, more powerful, and yield better fuel mileage then their "cheap" stuff. Most do, but some also add the same crap to all their gas, they just dont tell you. They want the consumer to buy the stuff with the higher markup as it nets better profits.

[Ewok]

Shell delivers its clean system additives in all its octane gas.

[IDBoating]

so if you fill the last tank of the season with a fuel that will still be just as spoiled come spring, takes more to ignite, and costs more, what was gained?

Precisely: It will be "just as spoiled" regardless of the octane rating.

What was gained is that premium fuel from Cenex in my area contains no ethanol. I don't care about the higher RON value. I care about not having ethanol. I'm paying a slight premium to keep ethanol out of my fuel system.

[chpthril]

Precisely: It will be "just as spoiled" regardless of the octane rating.

What was gained is that premium fuel from Cenex in my area contains no ethanol. I don't care about the higher RON value. I care about not having ethanol. I'm paying a slight premium to keep ethanol out of my fuel system.

For you specifically, yes, the absence of ethanol is a plus, but for for most in general, their would be no advantage to the higher octane, that was the point I wanted to get across.

[Timmy!]

Marine Formula STA-BIL

-BEST Ethanol Problem Fighter
-More than FOUR TIMES the Fuel System Cleaner than in Regular STA-BIL
-DOUBLE the corrosion preventer than in Regular STA-BIL
-Prevents corrosion from moisture & ethanol-induced water attraction
-Improves marine engine performance YEAR-ROUND, not just for seasonal storage

[IDBoating]

For you specifically, yes, the absence of ethanol is a plus, but for for most in general, their would be no advantage to the higher octane, that was the point I wanted to get across.

I completely agree. Unless they're using a modified engine, most boaters will not benefit from higher octane fuel and are just wasting money if that's the only benefit it delivers.

Also, the ethanol mixing practices vary state to state so perhaps someone can still get "regular" octane (read: less expensive) fuel without ethanol. I'm content spending the extra 20 cents per gallon (which at today's prices is about a 7% premium) to avoid ethanol.

One more detail: The addition of ethanol reduces the heat content (chemical energy) relative to non-ethanol fuel. I do not know the numbers, but in theory non-ethanol fuel will permit your engine to generate more horsepower than fuel "contaminated" by ethanol. Yet another reason to avoid it.

[Timmy!]

It's funny, in the automotive world racers are dying to convert to E85 since it is essentially cheap race fuel and in the marine world it's a death sentence due to it absorbing moisture.

[IDBoating]

It's funny, in the automotive world racers are dying to convert to E85 since it is essentially cheap race fuel and in the marine world it's a death sentence due to it absorbing moisture.

Then let the racing world have it. All of it. We'll take the pure gasoline, thank you very much! {grin}

[chpthril]

I completely agree. Unless they're using a modified engine, most boaters will not benefit from higher octane fuel and are just wasting money if that's the only benefit it delivers.

Also, the ethanol mixing practices vary state to state so perhaps someone can still get "regular" octane (read: less expensive) fuel without ethanol. I'm content spending the extra 20 cents per gallon (which at today's prices is about a 7% premium) to avoid ethanol.

One more detail: The addition of ethanol reduces the heat content (chemical energy) relative to non-ethanol fuel. I do not know the numbers, but in theory non-ethanol fuel will permit your engine to generate more horsepower than fuel "contaminated" by ethanol. Yet another reason to avoid it.

I have heard/read as high as 15% less energy and about 2-3 MPG drop from non-corn gas. So it takes more "foot" to achieve the same amount of work, and we need to fill up more often. So the latest debate is about what is really gained with ethanol blends. The tree-huggers dont see it, but many say that the amount of Co2 that is released into the atmosphere is about the same. Again, I have not seen hard numbers on this, but that is the new argument.

[IDBoating]

So the latest debate is about what is really gained with ethanol blends. The tree-huggers dont see it, but many say that the amount of Co2 that is released into the atmosphere is about the same.

Yes, that point has been made countless times in every discipline from politics to science. For the enviro's, I think it has become a matter of religion rather than fact. "Scoring a win" on ethanol blends was a major deal for them, and now it's more about not admitting error than it is about what's "better" for the environment. Never mind the net increase in CO2 emissions, increased food prices, etc. Apparently, for the enviro's the politics are all that matters anymore.

I'm doing my part by driving up demand for non-ethanol fuel. {grin}

[Ewok]

I have heard/read as high as 15% less energy and about 2-3 MPG drop from non-corn gas. So it takes more "foot" to achieve the same amount of work, and we need to fill up more often. So the latest debate is about what is really gained with ethanol blends. The tree-huggers dont see it, but many say that the amount of Co2 that is released into the atmosphere is about the same. Again, I have not seen hard numbers on this, but that is the new argument.

Car and driver put the number at 30% less energy per unit of volume so 30% worse fuel economy with E85. Big AG business is the winner, and we are all losers, unless we work for or farm corn, then you win.

[chpthril]

Car and driver put the number at 30% less energy per unit of volume so 30% worse fuel economy with E85. Big AG business is the winner, and we are all losers, unless we work for or farm corn, then you win.

Oh yeah, and Barack "give it away" Obama just signed a bill to further subsidise the growers to farm corn for ethanol.

[Timmy!]

Oh man, my buddy filled up his Suburban with E85 and we towed my boat with it to the lake and back (120 miles round trip) and he was at 1/4 tank when we got back. He filled up again and figured out that he got about 4mpg towing my boat to the lake. I was getting between 6-7mpg in my Avalanche at the time (same engine and frame as a burb).

Here in Colorado all stations have a 10% ethanol mix from November 1 to March 1 to lower emissions.

[IDBoating]

Car and driver put the number at 30% less energy per unit of volume so 30% worse fuel economy with E85.

Makes my 7% extra seem like a bargain, doesn't it? {grin}

[Timmy!]

Makes my 7% extra seem like a bargain, doesn't it? {grin}

Depends on how much the gas was compared to the E85 and the mileage you get with each. E85 can work out for some people but most of the time it's the SUV's that are the one's trying to make it work and it doesn't until gas is like 40% more than E85.