Fuel life

[vyv_cox]

There have been many threads here over the years, recommending a whole range of effective fuel life estimates. Here is my recent experience that surprised me a little and is in conflict with much of the advice given.

I live in Holland but still have a house in North Wales that we visit very occasionally. Last weekend was one of these occasions. In view of the very pleasant weather I decided to cut some long grass and nettles using a strimmer. The machine has been standing unused for more than 6 years. It was drained of fuel before we left it. In a cupboard in the workshop I found a plastic container of mixed two-stroke fuel that had about a pint left in it. This was at least six years old but quite possibly seven. Just for the hell of it I tipped this into the tank, checked that the spark plug looked OK, closed the choke and the engine started first pull. It ran perfectly well until the fuel was all consumed.

I also have a 1982 VW diesel camper. This stands all year round, battery charger comes on for 2 hours per week. On average it does 100 miles per year, usually in November when the MOT is due. Due to this low mileage the fuel in the tank has rarely been topped up throughout the six years. It never fails to start first turn of the key, except this year when the 1995 battery finally gave up.

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[DeeGee]

I have had similar experience, which conflicts with the received wisdom. I have been told that the higher fractions of petrol evaporate, and the resulting fuel will give trouble. But I have started lawn mowers after a couple of years, and outboards using containers filled two or three years ago, with no trouble. Not that I am challenging the received wisdom, it may just be a case of getting away with it because it was a fine sunny day, or a good engine, or....

<hr width=100% size=1>Black Sugar - the sweetest of all

 

[Sybarite]

As far as the Seagull is concerned I have trouble if I don't change it each season.

I have the same question regarding diesel engine oil. I found a couple of half used cans which are many years old. Does oil go off or not??

John

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[Russell]

I used 2 have a motorbike which would not start after the winter lay off, because the petrol had gone off. I could not even set fire 2 the petrol with a naked flame (in controlled conditions of course!) This bike had 2 run on leaded petrol, and it had an aluminium tank, so maybe this had something 2 do with it. Other bikes with plastic/steel tanks running on unleaded had no problems.
Another question while I'm here. Why does leaded petrol colour up tailpipes so u can tell what the mixture is like, but unleaded doesn't ?

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[tome]

I spent a couple of hours last weekend servicing our 4 stroke lawnmower. It was running very rough so I stripped the carb and poured the contents of the float chamber into a jar. It had some large globules of something foreign looking in the petrol, which I assumed were degraded fuel. It was ok end of last season but I'd left it full of fuel (naughty boy).

So that's my experience and I'd be inclined to drain the fuel in future. Can't say for certain what had happened, but I assume it was some form of deterioration rather than water.

On the other hand, my tractor which is an old '58 Massey Ferguson is always a pig to start but runs quite happily on 3 year old diesel.

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[brianhumber]

I would suggest it depends on the number of air changes of the air above the surface of the fuel. Petrol certainly contains volitile compounds which do evaporate, but these will saturate in a small volume of still air. If this air then changes due to the expansion and contraction of the air through the seasons then the fuel will tend to degrade.
Re Diesel, you can get this tested commercially, I have run and still do operate diesels on old fuel which we test every year out of underground storage tanks. I have a policy of returning the fuel after 5 years, for a sell price of approx 6p/litre, enabling the the storage tanks to be throughly cleaned and sterilized on a programmed basis.

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[DavidTocher]

I never drain the fuel (20:1) for my 6HP Vire at the end of the season and never have starting problems using the fuel stored in the boat tank over the winter. My Seagull (10:1) has started on the third/fourth pull (normal) with 3 or 4 year old fuel stored in the engine tank.

I always run the carb dry at the end of a day to prevent oily residues gumming up the carb on the boat engines but can't do the same with my chain saw (25:1) but again I never have any problems using last years fuel in the chain saw.

David

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[vyv_cox]

My thoughts too. Petrol in an open container will undoubtedly evaporate, totally if it doesn't have any oil added. Light ends will go first, inhibiting ignition if fed to a cylinder. Petrol in a closed container cannot lose very much. A carburettor bowl and fuel tank are open containers, although the vents may not be very large, but given enough time the light stuff will disappear.

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[bedouin]

I have once had problems with "stale fuel" in my 2-stroke outboard. It was running well until I filled it up with fuel from an old can (I don't know how old) Then it wouldn't start - however hard I tried. Draining the tank and carb and replacing with fresh fuel solved the issue.

I can't imagine diesel will ever have the same problems - I have used diesel that has been sitting in a boat tank for 10 years or more

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[Chris_Robb]

I have always been puzzled by this fuel aging thing. I started my fathers lawn mower on fuel that I know was in excess of 10 years old! I have never ever had problems with old fuel. Where you do have problems is on 2 strokes where evaporation has left oil behind.

I think the mythe - if that is what it is - comes from the old Seagull engine in which old fuel was always to blame - or was it a scapegoat?

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[richardandtracy]

Agreed.

The fuel is millions of years old anyway.

The problems I've had with carbs has always been due to gumming of the carb with the small proportion of heavy fractions left in the bowl. Additionally, the carb is a 'Heavy fraction concentrator' albeit an inefficient one, as the lighter fractions will be the ones more likely to evapourate into the carb throat while the heavy fractions won't.

Regards

Richard


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[oldharry]

Clearly some engines cope all right with older fuel (motor mowers, seagulls and the like) whereas more highly strung engines made by Honyamazuki and brothers dont. It was said of 80's/90s Hondas that even left unstarted for a week the carb bowls had to be drained and refilled before they would start!

The key factor seems to be the compression ratio. Yer average motormower has around 5:1 compression - and the Seagull even less! Many bike engines are double that to get the extra power so are much more susceptible to degraded and aged fuel. Also modern high power engines tend to run on much leaner fuel/air mixes which makes them more susceptible to fuel degredation problems.

<hr width=100% size=1><P ID="edit"><FONT SIZE=-1>Edited by oldharry on 11/06/2003 09:11 (server time).</FONT></P>

 

[Avocet]

There's a fuel permeability test that plastic car petrol tanks have to do as part of the type approval process. This makes me think that just because the fuel is stored in a plastic container with a tight lid it doesn't necessarily mean that the fuel can't go anywhere over a period of time. Whether or not the high-end losses are significant is another matter though!

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[ArthurWood]

Had similar experience after letting boat stand in storage for 4 yrs with full tank of petrol in sub-trop temps. Started on second turn of ign switch and ran fine.

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