How long for petrol to "go off"

[colinwcolclough]

How long for petrol to \"go off\"

One for the boffins here! We all know that petrol "goes off" and as such becomes a bit huffy about being used in a two stroke engine (although you can pour it into the car!) and we know roughly how long it is good for from the time it is poured into the tank, but....
How long has it been since the petrol was refined? Surely all the time it has been awaiting distribution, sitting in a tanker, been in the forecourt / marina tanks etc, it has been going off. How do I know that the petrol being poured into my reluctant two stroke is not already past its best?
Any ideas? It's just for interest really and I honestly do have more important things to worry about (just intercepting an anticipated thread there!).

 

[DepSol]

Re: How long for petrol to \"go off\"

Storage is the key element here it all depends on how its stored at what temperature and in what conditions. I have seen petrol turn to how could I explain it best Jelly or runny jelly. Couldnt really tell you for sure as dont really do petrol tests. I think six months with out use is started to push your luck.

Dom

I am boating again ;-)

 

[matt_lake]

Re: How long for petrol to \"go off\"

Also worth remembering it "goes off" quicker once 2-stroke oil has been added.

 

[adarcy]

Re: How long for petrol to "go off"

I believe petrol deteriorates and loses some octane rating but it must obviously be, as Depsol says, dependent on temperature and light.
As regards 2-strokes are you not confusing "going off" with varnishing?
I doubt if the octane rating reduces quicker with oil mixed in and 2-strokes are usually lower compression and only require 1 star. However, when the oil varnishes out you can seize your engine on it or worry about oiling the plugs up by putting fresh oil in.
I also seem to remember reading unleaded goes off quicker than leaded petrol used to and that is my experience. No doubt some of our professional fuel advisers will tell us why

 

[mtb]

Re: How long for petrol to \"go off\"

Yes it acts a bit like a laquer when it drys out in the carb ,some times causing problems re small jets. I normaly find the carbs get a white deposit between the float and or jets due to the disimiler metals .
Always best to not only drain out the float chamber but give it a spray with wd 40 for winterisation
cheers
mick

http://homepage.ntlworld.com/boats
I want a big steel ex trawler / tug v / cheap or swap for tug

 

[ArthurWood]

Re: How long for petrol to \"go off\"

Well, from personal experience, after leaving my 19ft /Merc I/O boat in storage for 4 yrs with a full tank in a sub-trop climate it started first time.

 

[Medskipper]

Re: How long for petrol to \"go off\"

Colin, I think your problem is the two stroke oil in the petrol, as already explained by others here, the only point I would add is that it is best to turn off the petrol supply after having used the engine and allow the engine to continue to run until all the fuel in the carb is used up! this will stop the jets being blocked by hardened oil in the fuel.

Barry


I just want to retire with my boat to the Med!

 

[ToMo]

Re: How long for petrol to \"go off\"

I didn't know that...now I'm really glad I bought a four stroke outboard.

TôMö