Old(ish) petrol - use or not - also how does fuel ages?

dunedin said:
Unfortunately it is tricky to dispose of last season’s unused fuel these days. But annual maintenance of neglect plus new fuel seems pretty effective.
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My local scrapyard charges me a 5er to get rid of any fuel and any amount, 5L or 30L its the same price across the board. He just adds it to the huge tank he has to run his machinery on. pure petrol and 2 stroke. Maybe worth asking as it can be a nightmare and expensive to get rid of old fuel by a licensed company.
 
Regarding aviation petrol in drums in a fuel dump (oz outback) it is considered ok for quite a few years but must be full drum laid on it's side with bungs horizontal so no air can get in. I suspect a lot of modern motors with electronic ignition are a lot better with old fuel than old magneto engines. However as said I would try to dilute it with new petrol or if does not have oil added just put it in your car a bit at a time. (with lots of good fuel) ol'will
 
My biggest concern would be that old petrol will absorb water if it can which can. (sealed container should be fine). Summer grade petrol is less volatile than winter, as there is a higher vapour pressure spec on winter fuel. (more Butane in the blend). I don't think the issue is how long you can store petrol, but how you store it. Re ethanol: I plan to run my outboard on super unleaded after September (less ethanol from then). Super unleaded has better additives than regular

Graeme
 
RichardS said:
Butane in petrol? I don't understand how this can be possible. :unsure:

Richard
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It's soluble in gasoline, I guess
Just like hydrogen chloride, ammonia, sulfur dioxide etc which are all gases at ambient temperatures are all highly soluble in water.
 
CalicoJack said:
I was talking to the workshop manager at a large marina last week and he was saying that 3 months is about the limit for fuel due to the amount of ethanol in it. He added that even with a ultrasonic bath he still has had occasions when the only answer has been to supply a new carburettor, which isn’t cheap.
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I had to buy a new carb for an outboard engine only 6 years old. White crusty deposits that the outboard agent said were unlikely to be shifted by U/S cleaning.
 
RichardS said:
Butane in petrol? I don't understand how this can be possible. :unsure:

Richard
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As Vic states butane is soluble in gasoline and is used to increase the vapour pressure of the final blend. RVP, or Reid Vapour Pressure limit is 100kPa in winter and 70kPa in summer. RVP is vapour pressure measured at 36deg C
 
Has anyone tried alkylate fuel? Aspen Alkylate Petrol | Alkylate Fuel | Aspen Fuel

Hideously expensive , but assuming you don't use much of it, the prospect of longer life, lower flammability and fewer toxic emissions are attractive and to some extent compensate for the additional cost. I use it for a small outboard and garden power tools but I use so little of it in both applications (which is why the long life is attractive) I can't really claim to have much data to go on. This season will be a good test of the 4-stroke fuel I bought in 2019.
 
Gentoo said:
As Vic states butane is soluble in gasoline and is used to increase the vapour pressure of the final blend. RVP, or Reid Vapour Pressure limit is 100kPa in winter and 70kPa in summer. RVP is vapour pressure measured at 36deg C
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The main use of isobutane is in refineries, as a gasoline – petrol – additive. There, isobutane is processed through an alkylation unit to make an alkylate. It is used to make isooctane, a high octane gasoline component, which increases the octane rating and anti-knock properties of gasoline.

Isobutane - What is Isobutane? i-Butane - What is the Use of Isobutane

Richard
 
Skylark said:
I had a car in my garage for a little over 20 years and it had half a tank of fuel. After prepping the engine it started at the first turn of the key.
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But obviously that's the petrol they sold a long time ago not the modern stuff....

I've had outboards run fine on ancient petrol.
My neighbor couldn't get his mower going the other day, on fuel bought last summer and kept in a proper can, fresh petrol sorted it.

It doesn't really matter how many people have got away with fuel how old, or how many people have had trouble.

Sometimes old petrol is just uncertainty you don't need.
You can either try it and see, or change it to be on the safe side.
I've seen enough cases of 'bad petrol' not to dismiss it, it's one of the easy things to try.

Th biggest problem is getting rid of any bad stuff, so I try to store the minimum.
 
TernVI said:
But obviously that's the petrol they sold a long time ago not the modern stuff....

I've had outboards run fine on ancient petrol.
My neighbor couldn't get his mower going the other day, on fuel bought last summer and kept in a proper can, fresh petrol sorted it.

It doesn't really matter how many people have got away with fuel how old, or how many people have had trouble.

Sometimes old petrol is just uncertainty you don't need.
You can either try it and see, or change it to be on the safe side.
I've seen enough cases of 'bad petrol' not to dismiss it, it's one of the easy things to try.

Th biggest problem is getting rid of any bad stuff, so I try to store the minimum.
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It seems there's quite a mix here of people who don't experience any problems and, on the other hand, people who feel they might have problems so do everything possible to avoid those problems. Maybe they don't need to be so diligent.
 
TernVI said:
But obviously that's the petrol they sold a long time ago not the modern stuff....

I've had outboards run fine on ancient petrol.
My neighbor couldn't get his mower going the other day, on fuel bought last summer and kept in a proper can, fresh petrol sorted it.

It doesn't really matter how many people have got away with fuel how old, or how many people have had trouble.

Sometimes old petrol is just uncertainty you don't need.
You can either try it and see, or change it to be on the safe side.
I've seen enough cases of 'bad petrol' not to dismiss it, it's one of the easy things to try.

Th biggest problem is getting rid of any bad stuff, so I try to store the minimum.
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The lighter volatiles will pass through some plastics, particularly the type used to make plastic fuel tanks for outboards and typical 5litre plastic fuel cans, so petrol will stay fresher longer in a metal tank. Cars have plastic tanks made from a multi-layer (laminated) process so there is a less permeable layer within a structural plastic. This is done to meet the ever stricter volatile/evaporative emission regulations which, as they get stricter over time may force the car manufacturers to go back to metal tanks.

Www.solocoastalsailing.co.uk
 
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I always add Honda additive to each can of petrol, used for my 2.3 Honda outboard and the 22yr old Honda lawn mower at home. I never drain the fuel out of either, the outboard started 2nd pull a couple of weeks ago as did the lawn mower. Also mixed as 2T for the strimmer. I can certainly recommend the Honda additive.
 
There are a few things here suggesting that old petrol wont ignite very well. The opposite is true. Petrol has stabilisers in that cause it to ignite at a controlled rate. This is why a spark is timed at before top dead centre. When the spark occurs the piston is still going up. it reached top dead centre at about the time the entire mixture has ignited therefor pushing the piston down with as much force as it can....

in old fuel these stabilisers evaporate and the fuel becomes MORE volatile. This means that when the spark occurs the entire fuel mixture is ignited very quickly and this does not give the piston time to reach top dead centre before the power of the explosion tries to push down. pushing down while the piston is still going up is bad news and can lead to complete mechanical failure even with holes in the piston.

I have heard varying times about how long this takes but one thing for sure is that petrol will go varnishy and could block your jets up. i have seen a tide mark in a very old fuel tank that literally looked like varnish scrapings.
again i've no idea how long this takes.

I have always used old petrol without issue but i do try to mix it up a bit with new.....
 
Topcat47 said:
I've yet to come across an outboard with a carburettor drain.
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FWIW I have Two Mariner 2T 5hps and both have a drain plug. I've never bothered to use it, seems to run fine on old fuel and with fuel left in the carb over winter. (The fuel tap was broken until this season so I couldn't run it dry.)
 
Mark-1 said:
FWIW I have Two Mariner 2T 5hps and both have a drain plug. I've never bothered to use it, seems to run fine on old fuel and with fuel left in the carb over winter. (The fuel tap was broken until this season so I couldn't run it dry.)
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Take two screws off and you can drop the carb bowl, clean the lot plus check the jet then reassemble - even a mechanical numptie like me can do this in under 2 minutes. Never used the drain screw.
 
The 100:1 mix in my OB has been there since before lockdown, I went down to check the boat yesterday and the OB started and got me to the boat and back without issue.
Needles to say, I don't believe in this stale fuel theory / myth.
The only thing that I do do is run the carb dry before I take the engine off the dinghy.
 
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