Does petrol really go 'off'?

**SMOKEU** · 14th September 2010, 15:08

I know that keeping petrol for years on end may cause the liquid to partially evaporate, leaving a solid cake behind (I've seen it before in a bike that hadn't been ridden for 10 years) but, will petrol lose some of its octane or otherwise degrade after a period of several months?

I'm only asking because I'm planning on buying enough fuel for the lawnmower to last 6 months because I don't like going back to the petrol station with a petrol can every couple of weeks.

**neels** · 14th September 2010, 15:11

Yep, because of the aromatics they added after the lead was removed to keep the octane rating up, these evaporate at a faster rate.

Probably not so bad in a sealed container as in a petrol tank though.

**imdying** · 14th September 2010, 15:11

Yes but not problem in your mower. If it's a stinkwheel give the can a good shake and you'll be right.

**MSTRS:Me** · 14th September 2010, 15:11

Lawnmowers don't really care. As long as the petrol still has some volatility.
I have a Rover/5hp Suzuki 2str that happily runs on premixed petrol that is over a year old.

**Mully** · 14th September 2010, 16:24

You can get petrol conditioner too - chuck X amount into Y litres (I forget the amount, but it's on the bottle) and it stops the octane from dropping.

**steve_t** · 14th September 2010, 16:31

IIRC, 6 months is the maximum length of time petrol should be stored for in a proper fuel container, but that's for vehicles. The lawnmower should be sweet as.

**slofox** · 14th September 2010, 16:50

My lawnmower never complains and it's fuel is totally neglected since I fuckin' HATE mowing lawns...

The chainsaw and the petrol hedge trimmer don't complain either and their premix is eons old...

**onearmedbandit** · 14th September 2010, 16:58

I'll have a hunt though my mag collection but a recent Superbike issue had an article on 'motorcycling myths' and included was the problem of fuel going off, which according to their fuel industry expert is a non-issue for even a couple of years.

**MSTRS:Me** · 14th September 2010, 17:53

Originally Posted by onearmedbandit

I'll have a hunt though my mag collection but a recent Superbike issue had an article on 'motorcycling myths' and included was the problem of fuel going off, which according to their fuel industry expert is a non-issue for even a couple of years.

A drop in octane is only a problem if that drop takes it below what your engine is optimised to run on.
That is why we can buy av-gas (leaded race fuel) at some petrol stations. The octane is way higher than a car/bike engine needs, but too low for aero engines.

**EJK** · 14th September 2010, 17:56

**scumdog** · 14th September 2010, 17:57

Originally Posted by onearmedbandit

I'll have a hunt though my mag collection but a recent Superbike issue had an article on 'motorcycling myths' and included was the problem of fuel going off, which according to their fuel industry expert is a non-issue for even a couple of years.

Got my brothers car here - has leaded fuel that was put in it say..1994.

STILL starts up and runs on it.

Modern 'petrol'? - dunno about that stuff.....

**munster** · 14th September 2010, 18:17

Can be especially bad in boats with underfloor tanks. I put in $20 or so of 120 octane Race Gas (Challenge Pukekohe has it) to refresh the fuel before each summer season. That and a bottle of Yamaha Ring Free to burnt the carbon off. Seems to work well for me.

In sealed containers or fuel systems it's not so bad. Boat underfloor tanks have a breather and all the aromatics / volatiles evaporate off over time.

My outboard mechanic also told me that it's a worse problem for 2 strokes, 4 strokes seem to be able to handle it better. He approved of my Race Gas use as well.

**hayd3n** · 14th September 2010, 18:42

the common red plastic petrol containers actually leach over time

**JimO** · 14th September 2010, 19:17

Originally Posted by scumdog

Got my brothers car here - has leaded fuel that was put in it say..1994.

STILL starts up and runs on it.

Modern 'petrol'? - dunno about that stuff.....

my 70 coon with a 302 in it hadnt run for about 5 years, poured some gas down the holley carb and cranked it for about 30 seconds, coughed into life, big cloud of shit out the back and away it went happily running on old gas