Petrol Going-Off - John Bullen
Does anyone have any experience of fuel going-off and then causing poor running if a car is stored for a few months? and if so how can it be prevented
Petrol Going-Off - Ian (Cape Town)
Maybe absorbing water?
Petrol Going-Off - Cliff Pope
Petrol "goes off" if it is kept in circumstances where it can evaporate. The most volatile elements obviously evaporate first, leaving a residue that becomes progressively less volatile and so the engine harder to start. Also gummy deposits start to form, most seriously in fuel pumps, carburettors and injectors.
I think it is generally better to keep petrol in a full container or tank, when there will be less exposure to changing air owing to "breathing" as the air temperature changes. The gumming effect can be reduced by adding injector cleaner beforehand.
Once you have a gummed-up carburettor you may well have to dismantle it and clean thoroughly before the engine will run properly.
But I think we are talking about long periods, not just a couple of months.
Petrol Going-Off - Cliff Pope
And condensation if the container is vented.
Petrol Going-Off - Cardew
I have had fuel problems with a chainsaw left unused for a long period.
Petrol Going-Off - JamesG
It seems to be more common with unleaded than with the old four star. Must be the different fractions in it I suppose. I've had it a few times in lawnmowers etc, I usually chuck it in the landrover tank (nearly full), get rid of it that way. Usually has a sort of varnishy smell.

Petrol Going-Off - JamesG
I Forgot to say, I think you can buy bottles of stuff which is supposed to stabilise petrol, I've seen it in lawnmower places, etc.
Petrol Going-Off - THe Growler
STP, Wynn's, Carplan and a few others all do gasoline stabiliser which absorbs moisture, keeps the lines and the carbs clean, and prevents tank rust. I use it in my bikes when I lay them up for the monsoon season, and also my emergency genset for power outages, which can go months at a time without usage. It works fine with no starting or gumming up problems when the time comes to crank 'em up again.
Petrol Going-Off - flatfour
I left my plastic gallon can in the garage for ages during the hot weather, then one day noticed that it had swollen up like a balloon, almost to splitting, the prussure inside was massive.
Petrol Going-Off - mark999
If you use fuel stabiliser remember to run the engine for a while to get the treated mix into the carb/injectors.
Petrol Going-Off - nick
Unleaded fuels do go off quicker than old leaded petrol did. This is due to lighter fraction additives needed to replace the effect of the lead in boosting the octane number. So now you breathe in a powerful carcinogen (benzene) when you fill up.
Petrol Going-Off - THe Growler
I said Carplan, sorry I meant Cyclo brand. I'm sure there are others too.
Petrol Going-Off - NARU
Frost do a fuel preservative which I've used for my bike and found OK.
Petrol Going-Off - Claude
OMC (Outboard Motor Corporation) who are the manufacturers of Mercury and Mariner outboards make a Petrol treatment fluid available from any boatyard or shop dealing in outboards. The benefit of this product is that it gives specific instructions for the dosage required to store petrol for up to 12 months and also different dosage rates for cleaning carbs or for winter lay up etc. I havn't found any other products that deal specifically with stabilising petrol for long term storage but I'd be very pleased to hear of any.

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