Off topic a bit long does fuel last?

Submitted: Tuesday, Jun 27, 2006 at 13:04
ThreadID: 35320 Views:8526 Replies:10 FollowUps:6
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When I'm travelling around the country I generally carry a 12ft tinny and a 9.9hp mariner outboard. The outboard is a 2 stroke job. I also carry a 12" Stihl chainsaw (usually). I generally mix up 20 ltrs of 2 stroke fuel for the outboard and a couple of ltrs separately for the chainsaw (Stihl don't recommend using oil designed for outboards in the fuel mix). Quite often I don't use all the fuel in the one trip and if the weather turns nasty can find myself bringing all the fuel home with me. Stihl recommend that you ditch fuel more than 3 months old.....Mariner don't have any recommendation in the handbook that I can find.
Given the ever-increasing cost of fuel and 2 stroke oil I'm finding it increasing against my Scottish nature to throw "old" fuel long is too long to keep/use fuel that has been mixed. What damage will say 6 month old fuel mix likely to do etc. What do you guys do to limit waste in this regard.
mmmmmmmmmmmmm maybe i'll just have to do a bit more fishing.

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Reply By: flappa - Tuesday, Jun 27, 2006 at 13:07

Tuesday, Jun 27, 2006 at 13:07
Just dump it into your Vehicles fuel tank , before you next fill up , just to dilute it a bit.

The little bit of 2 stroke oil wont make a lot of difference to your vehicle.
AnswerID: 180588

Follow Up By: Member - Beatit (QLD) - Tuesday, Jun 27, 2006 at 13:18

Tuesday, Jun 27, 2006 at 13:18
I've done this with plain unleaded (before I mixed), some was 12 months old. There has been some discussion on this and it is all about the octane rating falling below recommended and causing some engine glazing (if my memory serves me correctly). The amount propably isn't all that much and maybe do it in bits like Flappa says.

However, for my money I would be doing some more fishing.

Kind regards
FollowupID: 436857

Follow Up By: Member - Bill S (NSW) - Tuesday, Jun 27, 2006 at 18:28

Tuesday, Jun 27, 2006 at 18:28
HI Guys, Fish no Further,I keep telling you all FITCH is designed to keep Fuel FRESH,if you are travelling try it you have nothing to lose everthing to gain,no fuel wasteage.I can start my machines after standing for twelve months no problem,chainsaws,mowers,boatmotors the list goes on.If you are all so ignorant as not to try it well so be it.If every body used it there would never be a complaint about STALE fuel issues as with this, it just does not exist.For all country people I will offer a free F2t for every inline unit bought at the Henty Field day in SEpt.

Regards BILLS
FollowupID: 436917

Reply By: slammin - Tuesday, Jun 27, 2006 at 13:26

Tuesday, Jun 27, 2006 at 13:26
The main problem is that fuel is mixed according to the weather, temp, humidity etc and also that the fumes disperse over time.

However if you dilute or rotate the fuel no prob's that I've ever had.

PS If you were fussy enough where are you going to ditch old fuel anyway??

AnswerID: 180594

Follow Up By: Member - andrew B (Kununurra) - Wednesday, Jun 28, 2006 at 21:30

Wednesday, Jun 28, 2006 at 21:30
In a BIG campfire!!!
FollowupID: 437197

Follow Up By: slammin - Thursday, Jun 29, 2006 at 12:51

Thursday, Jun 29, 2006 at 12:51

Hey I like your thinking and it's nearly Territory Day too.

Break out the fire crackers!!!
FollowupID: 437292

Reply By: Sand Man (SA) - Tuesday, Jun 27, 2006 at 13:29

Tuesday, Jun 27, 2006 at 13:29

Being of Scottish heritage myself and also owning both a Stihl Chainsaw and a Mercury Outboard (Read Mariner) I can say that I have never experienced any difficulty with fuel that is several months old.

To my way of thinking, as long a the engine starts and doesn't run rough with lots of smoke (too rich) I'll use up what I have.

For the Stihl I mix up 5 litres at a time. (Usually only use this at home)
For the Outboard, 10 litres at a time.
As I usually have at least one 20 litre jerry of unleaded with me, I can mix up more Outboard fuel if required.



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AnswerID: 180596

Reply By: Member - Blue (VIC) - Tuesday, Jun 27, 2006 at 13:33

Tuesday, Jun 27, 2006 at 13:33
the fuel I've been using in my McCullock brush cutter and chainsaw must be at least 18 months old... I use both very rarely and always buy a 20l jerry of unleaded to mix as 2stroke which I then decant to 5l containers for ease of carrying. Both are now nearing 8 years old and neither has had so much as a plug changed, both still fire up and run well with a couple of pulls even after sitting for months...
AnswerID: 180597

Reply By: Mike Harding - Tuesday, Jun 27, 2006 at 13:37

Tuesday, Jun 27, 2006 at 13:37
Site Link

8.6 What is "stale" fuel, and should I use it?

"Stale" fuel is caused by improper storage, and usually smells sour. The
gasoline has been allowed to get warm, thus catalysing olefin decomposition
reactions, and perhaps also losing volatile material in unsealed containers.
Such fuel will tend to rapidly form gums, and will usually have a significant
reduction in octane rating. The fuel can be used by blending with twice the
volume of new gasoline, but the blended fuel should be used immediately,
otherwise teh old fuel will catalyse rapid decomposition of the new,
resulting in even larger quantities of stale fuel. Some stale fuels can drop
several octane numbers, so be generous with the dilution.


Sounds like the main issue issue is a reduced octane rating - won't bother most small engines, especially two strokes, much. I've used fuel which has sat in a plastic 25l container for over 12 months and couldn't detect any difference.

Mike Harding
AnswerID: 180598

Reply By: Alloy c/t - Tuesday, Jun 27, 2006 at 15:33

Tuesday, Jun 27, 2006 at 15:33
You need to do more fishing ? methinks you need to do more motoring in the boat to get to the fish ! Seriously though would not worry to much about stale fuel in the Mariner ,we bought a boat with a 10hp electric start 2stroke Mariner from a deceased estate just after xmas ,the motor had not been started for close to 3yrs ,fuel in tank was at least that old , 2 pumps on the primer bulb , started fist kick ,,
AnswerID: 180625

Reply By: Robin - Tuesday, Jun 27, 2006 at 17:03

Tuesday, Jun 27, 2006 at 17:03
My best ever finnancial investment was made when I brought a 60 litre drum of fuel once a long time ago at around 12 cents a liter.

About 10 years later I noticed the drum was rusty at the bottom and dumped the fuel into my Kingswood when fuel was around 65 cents and I never noticed any issues.

Robin Miller
AnswerID: 180647

Follow Up By: Gramps (NSW) - Tuesday, Jun 27, 2006 at 17:52

Tuesday, Jun 27, 2006 at 17:52
"12 cents a liter"

Bugger ! I'm getting all teary eyed LOLOL
FollowupID: 436915

Reply By: Patrol22 - Tuesday, Jun 27, 2006 at 17:45

Tuesday, Jun 27, 2006 at 17:45
Thanks everyone - can't see the fuel getting too hot around these parts for most of the year so I guess I'll just continue to use it way or t'other.

AnswerID: 180655

Follow Up By: Exploder - Tuesday, Jun 27, 2006 at 18:55

Tuesday, Jun 27, 2006 at 18:55
Stored correctly most oil companies will say it’s good for 1 year, but I suspect it would last a lot longer, petrol that is diesels a little different.

I have used old premixed fuel in a Still Farm Boss many times without issue; have also run 20Ltrs of 15-month-old 2-stroke throe a Johnson outboard with out a problem.
FollowupID: 436923

Reply By: HJ60-2H - Tuesday, Jun 27, 2006 at 19:19

Tuesday, Jun 27, 2006 at 19:19
You lose about 1 octane per week with fuel. So after 3 motnsh you start to see an effect. Some of the new 2 stroke motors are quite intolerant to old fuel. I fixed my neighbors lawn trimmer by changing the fuel. Went from wouldn't fire to start first pull. He thought I was a guru on motors after that.

After 3 months or so I burn the old outboard ad chainsaw fuel in the car.
AnswerID: 180677

Reply By: Member - andrew B (Kununurra) - Wednesday, Jun 28, 2006 at 21:39

Wednesday, Jun 28, 2006 at 21:39
I have similar issues myself, but the 2 stroke oil I last purchased (I think it was the yamaha or sthil brand, can't remember and the label has long gone off the bottle) was good for any 2 stroke, both air and water cooled. luckily I have an old 15hp Jono, which is very tolerant, only uses a 100:1 mix, so I don't go through much oil. I jenerally top up the mower and snipper out of the stale outboard tank, splash in a bit extra oil and don't have a problem. When we only had a Diesel cars it was a worry with fuel out of the 'big boat - only 17ft so no need for jealosy', now that we have a petrol car I put the spare boat fuel into the car and use fresh stuff in the big boat (Honda 4 stroke).

Cheers Andrew
AnswerID: 180923

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