Mixing Fuel onboard

[Neil]

You might think this a silly question, but has anyone got any tips for mixing / storing fuel ? The conceived problem is that I have two motors (a 15 hp Yamaha and a 3 hp seagull as backup). They each use a different 2 stroke mixture. So to carry premixed fuel on board means two containers plus the motors fuel tanks. Inevitably (hopefully too), this is going to mean atleast one container of unspent fuel, which is made to the wrong mixture for the main motor. I'm told fuel doesn't keep !

Do people tend to mix while afloat, what sort of containers are available for accurately measuring 2 stroke mixtures ?

Sorry if you think this is fuss about nothing, but I've got 5 gallons of unspent old 2 stroke fuel in my workshop which neither motor will start from, and nowhere that will take it !

Thanks in advance.

Neil.

 

[Guest]

I've used a syringe from a vet's surgery (not with a needle!) to measure exact quantities of oil into the petrol container. This works well.

Option 2, and perhaps an easier one, is to premix two containers for the different mixtures at the beginning of the season, but add the special stuff available from chandlers or mower shops (Mercury produce it under the 'Quicksilver' brand, or Briggs and Stratton sell it from mower shops) that prevents fuel from oxidising, and gives it a working life of a year or so. I'm told that without it fuel can oxidise in a month!

I hope this is useful.

Ady

 

[suzanne]

I use an oil which is in a container that has a measuring system in it. Its quite an old bottle and I don't think there available at present day, but keep looking you might find a decent measurer. Also I tend to use a funnel to transport oil to fuel. Im not sure if fuel keeps or not all that I do know is that we use fuel up to a year old at times that has sat in the garage out of season.

Suzanne xXx

 

[fjweaver]

I keep a baby's milk bottle on board for mixing - perfect for any thing between 5l & 20l

 

[Guest]

Concerning life of fuel, I mentioned in my earlier post that fuel lasts for about a month unless you add the special inhibitor stuff. I've been told by an outboard dealer that using older (oxidised) fuel can damage the carburretor, although I don't know in what way - is there an expert out there with an explanation?

Regards,


Ady

 

[Guest]

I think there is a lot of 'urban myth' out there re fuel etc. Lots of folk use petrol well over a month old and all over the world too, so if it were a real problem there would be a common awareness of it. I solve your dilema on my boat by only mixing fuel for the main engine but taking with me O/B oil so that I can 'step up' the ratio if I need the Seagull. By the way Seagulls run happily on a 25-1 mix if you are useing a modern O/B oil. This is 'greener' and less costly than the 10-1 engine oil mix used years ago.

 

[Guest]

I'm not sure what all the fuss is - or have I just been lucky?

I have a Mariner 3.3 for my Avon. I buy petrol in a 25 liter gerrycan, pre-mix the oil and then transfer from time to time to a small (2 gallon) metal cannister for the boat (I won't have a plastic petrol can on the boat for safety reasons). I keep the gerrycan at home. I usually end up storing unused fuel over the winter, which I use the following year without any problem. I fill up the Mariner tank at the end of the season and use the same fuel the following year without problems.

I think the key is to have well-sealed containers, ideally full (although mine usually are not). I think the problem everyone refers to arises when petrol starts to evaporate and oxydize, leaving being a gummy material, which can plug up the carburretor. With care, this need not be a problem. Talk of a one-month shelf life sounds nuts to me.

Incidentally, I try to avoid refilling the Mariner when on board, unless conditions are VERY calm (and no motorboat wakes). I keep it topped up whenever I am ashore on solid open ground.

 

[Guest]

Addendum to my posting above. Why not use the same petrol/oil mixture for both your engines. If one engine recommends 100/1, you can use 50/1 without any problem - it will cost you a bit more, and will pollute a bit more, but will in fact extend the engine life. You can probably even get away with 25/1. The accuracy of the mix is not that critical, but always err on the side of more oil than less.

 

[graham]

Re:Calibrated Syringes

Calibrated syringes are ideal for accurate measurement of the oil.Babies medicine syringes are available at chemist shops.(No needles on them).Using excess oil is environmentally unfriendly and the motor is more likely to stall at idling speed.

 

[Guest]

Re: Mixing Fuel onboard - definitive answer

Unleaded petrol (aka gasoline) is a mixture of light end hyrdocarbons ranging from the lightest butane (approximately 5% which gives you easy starting), through toluene and benzene (which gives the "anti-knock" properties) and on to what are called (at some refinerys) "reformates" (which give the calorific value that gives you good mpg).

When they are stored in a sealed container that doesn't start dissolving and contributing to the mixture (e.g. a steel tank) the gasoline stays the same for as long as the container stays sealed.

When you mix two-stroke lubricating oil with the petrol all it does is add another (heavier) hydrocarbon that doesn't "burn" when the petrol is burned in the cylinder. This lubricates the cylinder walls and prevents wear and overheating.

The "one month" rule is for open vessels. When open to the atmosphere the petrol (gasoline) will "weather off". This means that the light ends (the butane, pentane etc) will evaporate and what is left behind is a mixture of heavy hyrdrocarbons that will be very reluctant to ignite and let the engine "start".

With regard to the original query:

1. Pre-mix the highest ratio (i.e. 50:1) and keep it in a sealed container. If you then need a lower ratio you can add more oil.

2. Try to stay within a few points of the manufacturer's recommended limits. DO NOT change the ratio (as suggested by others). "More" is DEFINITELY NOT better. The old Seagull was/is a brilliant engine. However it has a very low compression ratio (just turn it over and see how easy it is) and it relies on the lube oil to seal the piston/cylinder interface and at the same time prevent excessive heat from damaging the cylinder and piston.

3. Modern engine designs have a much higher compression ratio than the Seagull and use higher revs to develop the power. They have much finer tolerances and too much lube oil in these engines will rapidly oil up the plugs (and even prevent starting) and running a high lube oil level regularly will create carbon deposits big-time on the cylinder heads.

If it's any help - I recently used about a gallon of 50:1 two-stroke petrol in a McCulloch strimmer for the garden without any problem. The petrol/oil mix had been made up for a Johnson Seahorse engine and kept in a metal can for at least three years!! (I was building a house and had very little time for sailing at the time.) The strimmer is still going strong and so is the Johnson.

Best regards )

Ian D

 

[Guest]

West Systems it is I think? sell syringes for mixing their resins. I use one of theses form 2t oil.

 

[Neil]

Re: Mixing Fuel onboard - definitive answer

Thank you all for your replies. I'm especially thankful for the technical explanation as to why / how fuel becomes less combustable with age. I think, I will do as suggested and premix at 50:1 then add oil as required for the seagull.

Thanks to all again.

Neil.

 

[RayJones]

I would strongly discourage you from mixing fuel on board for obvious safety reasons. I have successfuly used a synthetic two stroke oil called Opti for the last 6 years. It mixes readily , does not smoke or foul spark plugs and it is the only oil I have found that will not cause the fine spark arrestor screen in a chainsaw muffler to clog with carbon.
I have always used a 100:1 mix in my old evinrude 4hp outboard ( which I neglect badly ) but it always starts first pull. I use the same mix for my mower, chainsaw and brushcutter and have done for years with no negative effects.
In other words, buy a good quality synthetic 2 stroke oil, mix it 100:1 and it will go in anything.
P.S. Use fresh petrol as unleaded petrol goes stale after a relatively short time especially in summer.
Regards Ray Jones.