Fuel/oil deterioration

[Spruce]

I keep reading how much damage is caused by using old fuel in chainsaws, but I'm not clear whether this is down to using old petrol or an old mix of oil and petrol. In other words, is it ok to use petrol that's been stored in a tin for 6 months provided I only add the two stroke oil shortly before use?

 

I ask because I tend to use my saw fairly intensively for a couple of months in the spring and just occasionally during the rest of the year. My Husqvarna 345e manual says you should not mix up more fuel/oil than you can use in a month which kind of implies that it's the mixture that deteriorates rather than the petrol.

[spudulike]

I keep reading how much damage is caused by using old fuel in chainsaws, but I'm not clear whether this is down to using old petrol or an old mix of oil and petrol. In other words, is it ok to use petrol that's been stored in a tin for 6 months provided I only add the two stroke oil shortly before use?

 

I ask because I tend to use my saw fairly intensively for a couple of months in the spring and just occasionally during the rest of the year. My Husqvarna 345e manual says you should not mix up more fuel/oil than you can use in a month which kind of implies that it's the mixture that deteriorates rather than the petrol.

 

I gather fuel can go stale or off but the biggest cause of failure is the typical having a go at a large lump of wood using fuel oil mix that has been left in the saw for a few months. The piston gets too hot and melts on to the cylinder.

 

Always use at least 50:1 mix fuel to oil, always mix enough fuel for only a few days and don't use it if over 30 days old - stick it in your mower.

 

Lastly, drain the fuel out of your saws if you are leaving them on the shelf for a while - the fuel will rot your fuel pipes if left in the saw.

[GardenKit]

Its a bit of both really.

Firstly, the unleaded petrol is chemicaly 'unstable' and degrades due to oxidation which causes formation of resins (gums) and solids. These of course do no good to the carburation. The energy value also drops with age.

You will see the evidence firstly in the change in colour, fresh, neat, petrol is clear, but as it ages it darkens with the suspended solids.

 

Stale fuel effectively causes the engine to run lean as there is less usable fuel energy in relation to the air volume, lean siezure can follow as Spud has said while I was writing this.

 

Petrol now contains up to 10% ethanol which loves to absorb water from the atmosphere.

 

The oxidised, water laden fuel causes the oil to seperate from a two stroke mix, you will sometimes see the seperated oil combine with the water to form an emulsion coating the gauze filter in the carb.

 

Best all round to follow manufacturers instructions and use up fuel within 30 days, or use pure alkylate fuels such as Aspen or Moto-mix.

 

Others may disagree.

[geoff]

That about sums it up in my experience,you can get away with old fuel up to a couple of months old in a modern 4stroke motor,in a high reving 2 stroke you realy need to give it good fresh fuel,or suffer the potential problems that we all know about.

Get an old car or the like,& it will run on most anything,low compression engines designed for low/poor octane fuels,the old series ex military land rovers are a classic example,or go back a bit the fergie petrol parrafin tractors,get them warmed up on petrol & they will run on parrafin,a much thicker fuel.

Modern high performance/low emission engines,with todays 'petrol' are going to be fussy about what you put in the tank.