Identifying Bad Gas

[casuprock]

This is a pretty basic topic, but figured I'd share this because I got a good picture comparing old "stale" gasoline to fresh gasoline. Both samples in this picture are 93 octane 10% ethanol pump gas retrieved from the same station, 8 months apart. The left sample is old, the right sample is new.

In addition to the color, the smell of the old gas is rancid and similar to paint thinner.

You can also identify good gasoline because it has higher vapor pressure than stale gas since it hasn't lost all if its lighter petroleum compounds to evaporation. Stick your finger in the good gas and it feels cold evaporating from your finger. Old gas does not.

Pretty amazing...

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The conspiracy theorists would say that gasoline is designed to go stale so we're forced to buy fresh fuel instead of bulk ordering at lower rates like home heating oil diesel...

 

[turbodude]

Cool post, that's interesting. Never knew it would change color that much in 8 months! no wonder back when i was in the navy and i had to let my car sit for 6+ months at a time it ran like shit when i got back, hahaha.

 

[3kgt2nv]

I work for a aircraft refueling company and there are tests that have to get run on fuel that is called api gravity tests that measure the specific gravity of the fuel. the color isnt so important but the gravity is.

the reason color is not so important is with car gas they are allowed to mix in whats called trans mix from the pipeline shipment in certain percents, non name brand gas can add more because as long as its octane is correct the mix percent isnt as important. with name brand gas most limit it to 1 to 3 % by volume.

so the next question is what is trans mix

heres an example

this is a pipe line transporting fuel
_______________________________________________________

heating oil 93 octane gas jet fuel 89 oct gas diesel fuel

_______________________________________________________

as the fuel moves thru the pipeline it mixes together and forms trans mix (transportation mix) at the bulk storage facility they can separate this garbage out based on the specific gravity and then either send the trans mix back to the refinery to be reprocessed or they can mix it with other products to get rid of it.

It is common practice with all fuel manufactures to do this and its why name brand ie bp, hess, exxon/m all tend to run better because they very closely monitor what is actually in the fuel.

before we take a delivery we have to do tons of testing since its for aircraft. for a car gas station they just pull up and dump it in

just to explain the pic above when we get a fuel delivery of jet fuel the color can be coors light to clear and bright.

but yes old gas does burn worse because the volatile portion of the fuel evaporates or has absorbed water due to the hydroscopic nature of fuel (e85 more so). product like staybil and other fuel treatments help but if you left gas out eventually it would evaporate and lose enough water that it will thicken to varnish. there are remedies for this also and the most common is 5:1 mix with new fuel

 

[Zdrummer15]

Since color is caused by the trans mix, what causes gasoline to change color like above, or is just likely that the old gas was always that color? Or, is trans mix just one thing that can cause the gasoline to have a yellowish color?

 

[3kgt2nv]

color can be caused by several factors. where it was refined, where the crude oil is from, what the trans mix is made of, what additive packages the company adds (cheveron with techron) (shell vpower) etc

as far as trans mix coloring the fuel goes dump a single 2.5 ounce 2 stroke bottle of oil in 5 gallons of gas. it will look what ever color the oil is, usually green but the honda 2 stroke is red.

if you take the above example

1 gal = 128 ounces
5 gal = 640 ounces
2.5 ounces added of oil = 1/256 ounces of mix = .004% mix

way below the 1-3 % that major dealers allow but the fuel will still be way off color wise.

 

[casuprock]

Cool information about the aviation fuel. I've never met anyone who was involved in aircraft refueling or fuel distribution at all for that matter... 3kgt2nv, you are the fuel sage.

I should clarify (bad pun) that my "old gas" was clear and bright when it was purchased and there was a transition over time. I've watched it happen since I mow my lawn with this gas and see it every weekend.

 

[3kgt2nv]

I have a gas can that i leave in my shed all summer and it changes a little over the summer but I have never had it end up like that above. that I would think is either several years old or was contaminated at some point

 

[snooopy365]

I think the left gasonline was just colored like this when it was bought.
I have never seen a gasonline like the right one!
They all tend to be far more yellow colored.
It pictured one does have the same color as my E85 fuel.

I don't know if that is resulted in different fuel laws.
(I'm in germany, so can only talk about fuel here)