Thread: fuel (ULP) stabiliser

I only mix up what I can use in a couple of weeks, so that may mean only 5l sometimes, or if I'm cutting splits I'd mix up 10l for the day, just depends, but I definitely toss two stroke if it's been a month.

My Chainsaw Mechanic put me onto Premium Unleaded. I mix up 10L at a time and it still works OK in my saw after 2 Months. I use it in the Brushcutter,Lawnmower and Blower/Vac. The Regular Unleaded mix would only last 3 weeks.

Cheers,
Jon

Fuel has a short shelf life and begins to deteriorate extremely quickly. Also it is not a good idea to use E10 type products (just in case you are tempted) as they are not compatible with plastic products, which may be found in chainsaw carburettors.

Certainly some small engines are more tolerant of old or "stale" fuel than others.

Regards
Paul

Stale fuel is fuel that has been partially broken down following interaction with oxygen, water and heat.

If you want fuel to last then store it in air tight containers with as little air as possible above the fuel in as cool a place as possible. One trick is to buy a set of smaller (eg 1 litre containers) and transfer the fuel into these "shots" so you are not opening and closing a big fuel container all the time. This also helps prevent water buildup in fuel in the bigger container.

The other thing is not to put fuel in containers that contain even a small amount of old fuel so make sure the storage container is empty before refilling.

The break down causes a significant reduction in the octane rating and a loss of 3-5 octane points over a few months, so 91 octane effectively becomes 86 octane.

This has been discussed before but most operators do not realize that Stihl recommends using a minimum of 94 RON octane rating on their bigger saws. This does not mean saws will not operate on fresh 91 RON, but if you purchase 91 RON and leave it sitting around for a few months by the time it is used it could be 87-88 RON. Probably because of this the Stihl manual states "if the ULP is less than 94 RON then use premium unleaded".

In summary, unless you are talking large volumes of fuel storage then there are many things that can be done to mitigate the break down issue.

Just a question on this subject, what happens when you do use the stale fuel? Could it cause damage or just a lack of performance? I wasn't aware of this short shelf life and often used fuel of months old.

Originally Posted by Bernt

Just a question on this subject, what happens when you do use the stale fuel? Could it cause damage or just a lack of performance? I wasn't aware of this short shelf life and often used fuel of months old.

Depending on the compression ratio a low octane fuel will cause pre-detonation (also known as pinging) this damages the piston and puts stress on the rest of your saw. It can hammer the ring gaps down and pinch the rings.
Anyone who has seen the dramatic effect PD has had on a high performance car's pistons (looks like a sledgehammer has been used on the top) would steer well clear of ULP and go premium everytime. It is only a small extra cost if you are only feeding a chainsaw.

Originally Posted by Bernt

Just a question on this subject, what happens when you do use the stale fuel? Could it cause damage or just a lack of performance? I wasn't aware of this short shelf life and often used fuel of months old.

It depends how degraded it is. If the fuel is fresh to begin with and kept in a clean airtight container with only a small air head above the fuel and has been kept in a cool place even after 12 months there will probably just be a loss in performance and VV.

I just don't think it's worth mucking about with old fuel.

Originally Posted by Bernt

Just a question on this subject, what happens when you do use the stale fuel? Could it cause damage or just a lack of performance? I wasn't aware of this short shelf life and often used fuel of months old.

Bernt, my faithful old Harry the Husqvarna is in the shop right now, was using him to fell and dock billets for splits and he just stopped dead. Couldn't get him started for regardless how much I tired my little old arms on that pull cord - turns out even though I have recently gone from 50:1 to 25:1 he experienced a low oil failure $300 later he should be back on line. That saw hasn't skipped a beat for 7 years, sitting next to the mill, just been normally serviced and all I can put it down to is old fuel

if you have gone from 50:1 to 25:1 you have increased the oil

Did the saw run low or out of fuel? I didn't know about this but a mate who used to be a comercial tree lopper recently told me that his husky did some damage to the piston & left alloy deposits on the bore (but not damaging the bore) when his saw ran out of fuel, he said as fuel supply dropped the RPM's screamed then the saw stopped, compression went down, a new piston & ring was needed

cheers,
Dean.

running low or out of fuel wont do that damage his saw would have been running lean

Yeah I understand going from 50:1 to 25:1 is upping the amount of oil, hence why I feel it was bad fuel not a problem caused by lack of oil. I've had heaps of times the fuel has run out during cutting - almost every tank, 'runs out' during use, so cant subscribe to the theory low fuel or running out of fuel causes damage

Originally Posted by tlbsg

running low or out of fuel wont do that damage his saw would have been running lean

Thanks for that advise tlbsg, running lean sounds more logical, I'll tell him that!!. My old husky runs out of fuel often too & has never had a problem

Dean.

Originally Posted by tlbsg

if you have gone from 50:1 to 25:1 you have increased the oil

when increasing the oil it makes the saw run leaner