Does the octane in gas evaporate? Really?

JamesJems · Feb 5, 2007

Alright. I took everyone's advice and am only using fuel less than a month old. Standard Stihl 2-stroke engine oil and some 93-octane from the local filling station. But if I keep some of the mix in a rubber gasket sealed aluminum fuel bottle, will the gas degrade? (I'm guessing no) Could I keep it sealed indefinitely and use it later, when I need it?

I already took the leftover in the plastic gas can a poured it in my truck's gas tank.

James
(MS260 Killer)

livewire · Feb 5, 2007

fuel does degrade

I use stabil when I want to store for longer periods. I think others here do too!

livewire · Feb 5, 2007

Premix!!!

Stihl premix has fuel stabilizing agents in it too! I don't know how effective it is, though! I think "indefinately" is a little too long to keep.

Even STABIL-ized fuel has a lifespan depending on how much you use!

I read too fast sorry bout that!

troutfisher · Feb 5, 2007

JamesJems said:
Alright. I took everyone's advice and am only using fuel less than a month old. Standard Stihl 2-stroke engine oil and some 93-octane from the local filling station. But if I keep some of the mix in a rubber gasket sealed aluminum fuel bottle, will the gas degrade? (I'm guessing no) Could I keep it sealed indefinitely and use it later, when I need it?

I already took the leftover in the plastic gas can a poured it in my truck's gas tank.

James
(MS260 Killer)

YES! gas does go bad. Heat makes it happen faster. Octane is what gives gasoline it's ability to resist pre-ignition. In high compression engines gas will ignite from compression alone, before the spark plug sparks. If the fuel charge ignites before the piston is past top dead center, the connecting rod is still vertical, and the piston can't be pushed down. The piston rings like a bell and you hear "spark knock". Even worse, the fuel charge ignites even earlier and the piston must compress a burning cylinder. That poor piston won't last long. Use up your gas, and buy more. I dump it into my lawnmower or snowblower.

gatkeper1 · Feb 5, 2007

Storing gas in a metal airtight container will give you the longest time before the gas deteriorates. Gas goes bad from the evaporation of volatile compounds and exposure to air, water vapor and heat.
With 2 stroke fuel I only mix what I will use within the month and discard what I do not use

sedanman · Feb 5, 2007

Octane does not evaporate. Octane is a rating not a chemical. What DOES evaporate first in gasoline is the "light ends" or light aromatics, these are the v.o.c.'s that make your engine easy to start. Gasoline is not a chemical it is a compound.

Bob Wright · Feb 5, 2007

Here are some of the "light Aromatics" used.
Benzene, Tolulene, Butane, Naphthalene, Methyl Tertiary Butyl Ether, Ethanol, there are the light ends that will evaporate from the basestock as sedanman said. There are prob more but i just make the stuff

....Bob

Does the octane in gas evaporate? Really?

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