Petrol shelf life?

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Hi all, i've been trying for quite some time to find a definitive answer on the question of petrol shelf life without success, the answers i have found are very different and range from four weeks to twelve months.

So, does anyone know or have any definitive info about how long petrol will last before it starts to go off (without stabilizers) if left stood in a fuel tank, bike and car?

Thanks.
 
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I don't have a definate answer but this is in my experience:

I've started up low tune engines such as lawn mowers, strimmers and generators on 1-2 year old petrol before. They don't seem to mind one bit.

Bikes, cars and other high performance, high tune engines (yes even a 1.0L corsa engine is high tune, in comparison to the above anyway! :D) are normally ok on anything up to 6 months.

In the race bike petrol from cans left over winter (4-6 month gap) will run like crap (but works fine in the family hatchback so it goes in there) but anything left from 1 race to the next (up to 2 months between) seems no different at all.

So:
< 2 Months - Perfect!
2-4 Months - OK for almost everything baring high performance engines
4-6 Months - Bit iffy, but seems ok in day to day cars
> 6 Months - Only good for agricutural uses ;)

EDIT: As mentioned below it depends on storage conditions, the above is on fuel stored in 20L metal jerry cans filled to the brim.
 
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Hi all, i've been trying for quite some time to find a definitive answer on the question of petrol shelf life without success, the answers i have found are very different and range from four weeks to twelve months.

So, does anyone know or have any definitive info about how long petrol will last before it starts to go off (without stabilizers) if left stood in a fuel tank, bike and car?

Thanks.


You cant get a straight answer because there are too many variables to take into consideration.

If the petrol is stored in an airtight container and it is kept full to the brim so there is no air in there, it shouldn't go off at all because it would be unable to evaporate.

If its kept in a vehicles fuel tank then it will go off as these are not airtight. The length of time it takes to go off will also depend on how much petrol is stored in the tank as well.
 
Petrol is already a few million years old and stored correctly I can never see it going off.

However, particulate and/or water contamination due to storage in a crappy container in your shed will cause it to degrade.
 
Thanks for the input guys, my bike has always been in use over winter (stood for two weeks at most) so never needed to ask these questions, but at the moment there is no way i'm taking the bike out and it's been stood for about five weeks now, my bike is kept in a brick garage where there doesn't seem to be any sign of condensation forming on the bike, with the low temps we are experiencing at the moment roughly how long do you think the petrol will last before i need to start thinking about it going bad?

Thanks
 
I'd say that in the fuel tank while stored in a garage you will be safe for at least 1-2 months. Don't worry about it :)
 
Thanks for that Dureth, much appreciated, there is only about a gallon of juce in the tank so i'll just fill up with fresh stuff when the snow thaws a bit.
 
The shelf life of fuel is longer than the duration between the posts asking how long the shelf life of fuel is :D

If in a sealed container, with no light, can last 2-3 years, but may not run as well as fresh fuel. If either of the previous 2 conditions dont apply, 1-2 months in warm weather 2-3 months in cool weather.
 
Erm, whoops. Get ready to have a laugh at my expense: My car has been off the road for about 9 months now. Full tank of fuel :(

Between all the other things I've done with it, didn't think of fuel. It useless then? :(
 
it does lose its 'bang' after a while in terms of performance but my bike still starts up on petrol i got for it 2 years ago. generator still works too, all i have to do it clean the spark plug first as petrol has clogged it.
 
SuperBike Mag said:
Does petrol go off over time?
All sorts of problems are blamed on petrol that's "gone off" either in a bike's tank or in a separate petrol can. Is this really a problem, and, if so, how should you combat it? We've heard the same about brake fluid, so is that the case too?

Once again, it's over to the cleverest bloke we know, John Rowland, Fuchs Silkolene's top automotive research chemist to cut through the internet hype and give us the facts.

"Petrol in a sealed metal can does not go off, provided it is purchased in the UK or any other more or less civilised place. It will be OK for years. About the only additive in fuel is the detergent which doesn't evaporate. In these lead-free days, octane number depends on the molecular make-up of the fuel, and all you need to do is stop evaporation. Even the smallest molecules in there (such as hexane) can't get through metal. Plastic, as used for fuel containers, is itself made up of long-chain hydrocarbons (usually high-density polyethylene) which have similarities with the short-chain petrol hydrocarbons, so small petrol molecules worm their way into the relatively large spaces between the plastic molecules and get out the other side. Losses can be several percent over long periods (months) but thick plastic helps reduce this. You can't beat metal with its compact atomic structure for storing petrol."

"Petrol is OK in a can with an airspace; a tiny amount of the more volatile fractions of the fuel will evaporate to fill the airspace, and that's the end of it. It becomes a 'closed system in equilibrium'. Molecules go back into the liquid phase at the same rate as they leave it and enter the gaseous phase. Even a three-litre airspace in a five-litre can will only contain a very small amount of fuel vapour, equivalent to one or two CCs of fuel depending on the temperature."

"As for a vented fuel tank like most bikes have fitted, there will be some minor vapour loss of the more volatile fractions, such as hexane, but nowhere near as bad as losses from a container exposing a large sufface area of fuel to the air - such as a frying pan."

"Volume changes in the tank airspace due to daily temperature changes cause the tank to 'breathe', but one breath every 24 hours isn't so bad. Even a few months of this with a half full tank isn't a big deal. I get the impression from some bike owners that they think the fuel tank gasps away like an elephant running a marathon. In reality, it's more like a hibernating dormouse. Imagine a 16-litre tank with an eight-litre airspace, starting at 10C it cools to 0C. Using Charles' law, we can calculate the tank would draw in 300cc of air, and blows it out again when it warms up to 10C. But, petrol vapour is heavy, and the air drawn in will tend to sit on top of it, so, when air is lost when the tank warms up, it will be mainly the top layer with only a small amount of fuel in it."

"As for petrol evaporating from the carbs, some fuel, particularly from non-mainstream suppliers, can leave a tacky deposit when it dries out, but this was more of a 1990s problem. You don't hear of it happening today where civilisation (as we know it) exists. Even so, it's a good idea when putting a bike in storage to add a drop (5cc/litre) of good two-stroke oil to the fuel, run the engine until it's good and hot, shut down and cover with a thick blanket (cuts temperature fluctuation). Then, if the fuel dries out, a protective oily film will be there which is easily washed off when the bike is run again."

"Brake fluid (avoid the cheap stuff) will keep for years in a sealed, full, plastic bottle. Even a part-empty bottle is OK if the top is on tight. People worry too much about this water-absorption business. OK, it happens, but it's a slow process. Anyway, the boiling point of damp brake fluid is around 190C, so, unless you're out to bust the lap record at the IoM, it's not going to let you down."

In summary, fuel and brake fluid are unlikely to go 'off' unless stored incorrectly for years rather than months.

Sounds good to me! :)
 
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I just tried to get my 125 back on the road after not being ridden properly for a couple of years. It only had a brief outing 9 months ago when I was thinking of selling it, can't remember if I topped up with fresh petrol then, but I don't think I did.
Anyway, I tried everything I could think of. One of the first things I've allways done in the past is to empty the carburettor. This has always worked, but not this time.
So after reading this forum I emptied the 4 litres that were in the tank (it did look just like ****, as another poster has commented). Put in fresh petrol and it fired up streaight away, running perfectly.
So the petrol DEFINITELY can 'go off'.
 
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