Petrol "shelf life"

MustRib · 22 November 2007, 19:34

Just wondering if anyone can give me a definitive answer to the "shelf life" of the unleaded in my plastic fuel tanks?

Matt · 22 November 2007, 19:42

Yes. Variable.

Nos4r2 · 22 November 2007, 19:42

About 3 to 4 months depending on if it's premixed or not. Premix goes off a bit quicker-around 3 months.

That's before it starts to smell funny.

If you're leaving it over the winter grab some fuel stabiliser from your local lawnmower centre or chandlers (same stuff, more money )

MustRib · 22 November 2007, 20:39

thanks Nos
hmmm .. think I will be using whats left in the SIB tank to have a bonfire or a barbecue!
Have to get out in the Rib in the next few weeks then. Wish the weather would pick up a little

prairie tuber · 23 November 2007, 05:17

The biggest reason I like oil injected 2 strokes over pre-mix is that when I'm done boating, I can simply dump the left over fuel in my marine jerry cans back into my truck's gas tank.

GuyP · 23 November 2007, 12:24

Quote:

Originally Posted by MustRib

Have to get out in the Rib in the next few weeks then.

Or just add some fresh fuel to the stuff in the tank the next time you want to use it.

I reckon all this fuel 'going off' stuff is nonsense anyway. It'll still work, it doesn't mysteriously become uncombustible

(speaking from experience of non pre-mix that is)

Nos4r2 · 23 November 2007, 13:43

Quote:

Originally Posted by GuyP

Or just add some fresh fuel to the stuff in the tank the next time you want to use it.

I reckon all this fuel 'going off' stuff is nonsense anyway. It'll still work, it doesn't mysteriously become uncombustible

(speaking from experience of non pre-mix that is)

Come and smell the non-premix I've got in a can in the garage that was used for cleaning down last year.It smells like parrafin and I could probably throw a match in it without it lighting.

MustRib · 23 November 2007, 14:09

Sort of my point really....anyone on the forum with petrochemical experience/knowledge who has the "official" answer to this or can expound with the science behind whats at play in determining shelf life?
I dont want to use "bad" petrol.

cheers
Andy

MustRib · 23 November 2007, 14:10

and its too bloody expensive just to chuck away!
I have half a tank for the SIB last used in May thats pre-mix and a tank full of regular (not pre mix) from end of August on the RIB.

DJL · 23 November 2007, 14:46

Most petrol manufactures give the storage life of petrol to be around one year.

So even in less than ideal boat tanks I wouldn't worry about leaving neat petrol over the winter. You're probably better toping the tanks off to keep the amount of air/moisture in the tank down.

Poly · 23 November 2007, 14:48

Quote:

Originally Posted by MustRib

Sort of my point really....anyone on the forum with petrochemical experience/knowledge who has the "official" answer to this or can expound with the science behind whats at play in determining shelf life?
I dont want to use "bad" petrol.

I am not an expert in petrol per se, but it certainly can go "off". There are three effects:

(1) Evaporation of the volatiles, e.g. methanol. This reduces the flammability and the octane (potentially affecting starting and performance respectively).
(2) Gums/waxes start to form, largely by oxidising when in contact with air. Those gums can block filters/injectors/carbs etc.
(3) Microbial contamination - much less of a problem in petrol than diesel - but if there is water around bacteria can grow in fuel - which will degrade the performance and eventaully produce deposits etc which block filters etc.

Problems will be reduced by: storing in a well sealed container (to reduce evaporation). Storing the container full (to reduce oxidation, and leave no space for condensation). Storing at low temperature (to reduce evaporation, potential for microbial growth and rate of oxidation).

Fuel stabilisers presumably contain agents to reduce the oxidation rate.

Unless there are stabilisers added to the fuel - things may be worse with "modern" fuels than in the old days with leaded fuel - as they tend to contain more oxygenates to improve emissions and increase octane.

Stick it in your car (assuming it is not premixed) - preferably mixed with some good fuel - even if the worst happens at least a break down is not at sea.

Poly · 23 November 2007, 15:01

Quote:

Originally Posted by DJL

Most petrol manufactures give the storage life of petrol to be around one year.

Do you have a reference to that? Do they spec the storage conditions? Is that 1 year from purchase at the forecourt or from manufacture?

DJL · 23 November 2007, 15:43

I've got some fuel spec sheets from a few years ago, but i'm don't think they are public info so i'm not willing to post.

However, you can find brief comments about storage on the BP site.

"As general guideline, fuel stored in sealed containers and under shelter will be suitable to use for about 12 months. If the container has been opened or stored outdoors, especially in the sun, storage time should be limited to 6 months."

and

"When stored under appropriate conditions, the storage life of BP Ultimate is one year. Note that the volatility of BP Ultimate will change monthly so that there are seasonal variations in composition. "

http://www.bp.com/liveassets/bp_inte...P_ultimate.pdf

Limey Linda · 23 November 2007, 16:19

This may help explain the variables
http://www.straightdope.com/columns/060825.html

Hightower · 23 November 2007, 16:26

When lay Kohaku up for 10 months I topped off the tank. Whe I came to use her again I part emptied the tank (about half full) syphoning the fuel into my cars and topped it off with some fresh fuel, didn't have any problems.

truble · 23 November 2007, 23:27

you can buy a fuel sniffer that will give you a RON ,octane reading,,,we use them to check fuels in race karts during scrutineering and racing,,but simple tests have shown,,that within 72hrs in a shaded cool enviroment,,elf 104,,,will lose near 2points,,,,shell vpower 100 oct,,will be stable a bit longer but 100hrs is about the time b4 losing octane,,and the simple reason is,,when u take the cap of the drum u hear an escape of air pressure,,well thats your octane going to atmosphere,,we tested a 5ltr steel tin by put fuel in from pump,,sniffed at 98,,then shook can,,released pressure,,got 97,,after 15mins we had 92 and that oct at hi revs is just like kerosine,,rubbish,,,u can doctor ur fuel with naptholene,,,try a test,,put fuel in a glass,,250ml,,add a napholene ball,,(moth ball),,watch the bubbles,,,thats oxygen in the fuel,,and thats what gives u power,,aromatics are used these days to improve oct as lead is a bad thing,,lol,,dont put lead sinkers in your unleaded cars,,burns out the catalyic,,but naptholene works well,,2 balls to 20lrs fuel gives approx 1point ,,the moral of the story is,,use the fuel in ur boats and try not to store it for to long,,bad fuel will create more heat in combustion chamber,,

MustRib · 24 November 2007, 01:04

great replies folks...
I like the idea of mothballing the petrol rather than the boat

Nos4r2 · 24 November 2007, 06:52

Quote:

Originally Posted by MustRib

I like the idea of mothballing the petrol rather than the boat

I wouldn't... the solid stuff has to go through your engine too