old gasoline 1

[jarvis]

I figured this would be the best place to ask this(these) question which I have pondered so often. Why does gasoline go bad? Also can it be reversed? How long is it recommended to keep gasoline? What do products like Stabil do and how long do they extend the life of the gasoline? Thanks in advance for the insight.

Ben Englund

 

[1Bluegrass]

I'm not at all an expert on gas formulation, but over the long term and school of learning, I do know that that gas is a formulation science that varied per refiner, time of year and area of distribution.
Gas formulation is composed of a number of different chemicals in addition to base stock.
These have various rates of evaporation and photo chemical sensitivities. Without getting into chemistry; over time these migrate out of formulation leaveing the heavier content behind as heavy parts, gum and varnish.
This shows up as a very different odor, will not burn in an engine etc.
One can see all these effects from leaving a lawn mower with gas in the tank for a year and trying to start it the next season.
Keeping gas long term is best done in an air tight, light tight containers with some additive special for extending gas life but in no case go over a year, especially if stored for emergency generator use where it may not be used very often before being replaced.

 

[drwebb]

Gasoline has a lot of unsaturated molecules in it. That means it can react with oxygen over time in the air. If you remember linseed oil varnish, it's the same idea. These oxidized products are not as soluble in the gasoline and will agglomerate and plate out. Stabil and other preservatives contain antioxidants that inhibit this reaction. They can probably extend the 'life' of stored gasoline by 2 to 10 times depending on treat rate, but times what depends on air circulation, temperature, relative humidity, other contaminants in the gas, ground level ozone, phase of the moon, etc. etc.

 

[jarvis]

hmm..... thanks guys.

So I guess storing gasoline for decades is out.....

Ben Englund

 

[jarvis]

How about diesel fuel? I know it gells, but can it be stored for years and still used?

Also will nonoxygenated gasoline last longer than regular gasoline?

thanks

Ben Englund

 

[swall]

It may be my imagination, but it seems that 2 stroke mix gas keeps forever. I have taken chainsaws with two year old gas, no Stabil, and they start right up.Anybody got comments?

 

[patprimmer]

2 stroke is the most unstable.

Normal gas can oxidise if exposed to air, and different components will evaporate at different rates leaving the fuel with a higher concentration of the less volatile fractions, however, if kept in a sealed, full drum, it is fairly stable.

2 stroke contains oil. The oil reacts with the octane boosters, and reduces the octane of the fuel and the lubricity of the oil mix. If you get more evaporation of the fuel than the oil, it also ends up oil rich, enhancing lubricity, but further compromising octane. This often gives no real problem, but can result in extra wear, and can result in detonation, which can then quickly destroy an engine

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[swall]

So Pat,would your answer change relative to 50:1 mix vs 16:1 two stroke mix?

 

[patprimmer]

I never thought about it, but I guess the more oil, the more the potential loss of octane

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[ewh]

I have recently read in and old car magazine about adding the preservative BHT to gasoline in stored autos. It appears to extend the life of the gas. Any thoughts or comments?

 

[swall]

Maybe BHT is what is in Stabil. I looked up the MSDS sheet for Stabil, but they claim that the 5% that is not petroluem distillates is proprietary.

 

[Strider17]

It seems to me that as the concentration of oil
in gasoline, or two-stroke fuel, increases,
the octane would increase since combustion of
the fuel would be more difficult. IMHO...

 

[1Bluegrass]

The oil mix for 2 cycle is a precision deal for hi performance such as Kart racing.
To much and the engine goes lean and sticks a piston from excess heat. Remember that the oil is metered though the carb in most engines along with the gas.
Too little oil and the piston still sticks fast from lack of lube.
This means there is a window that has to be maintained.
.
In 4 cycle engines, oil in the air/fuel reduces the octane rating of the the "atomized" charge in the chamber at that time and can change with rpm and engine load not to mention carbon deposits that change the process as time goes by.
.
Then to get deeper into this for both types of engines, one has to deal with plug heat range and ignition timing.
The results of all this can be preignition, and detonation brought on by the effects of the oil.
It becomes quite an education to figure out what is going on at any time. Is it to hot a plug, is it to much oil, is it to much timing etc. So it can get quite involved by using an exhaust gas temp gage etc.
Close records of mix and changes, are needed if this is for hi performance because it gets costly losing engines to often.

 

[patprimmer]

It it not my opinion, It is a fact that oil reduces the octane rating of petrol.

I am at home so I don't have the links available

When I am in the office, I will post some links to some research sites that document this.

The best site is NACA, which is the precursor to NASA. It contains a lot of research on aircraft engines in the early part of the 20th century and during WW11

I will see if I can find it vwith google

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[patprimmer]

Here is ne link

http://naca.larc.nasa.gov/

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[patprimmer]

This one will give you all the facts you need about motor fuels

http://blizzard.rwic.und.edu/~nordlie/cars/gasoline.html

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[jarvis]

Wow.... Thanks Pat for the very informative answer and the links. much appreciated.

Ben Englund

 

[drwebb]

I suspect BHT (Butylated Hydroxy Toluene, or 2,6-di-tert-butyl-4-methyl phenol) or similar hindered phenol is what is used in BHT. You need less than 0.5% to get the effect, so that's why Stabil is only 5% AI.