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Old Petrol mix


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Hi everybody,hope you all had a good Christmas :D

Thinking of flying tomorrow weather permitting and have a full tank of petrol that I mixed in October.

Should I drain it and make a fresh mix.

In my old DK manual they said to dump the mix if it was over 4 weeks old .

You can use it but you will be down on power a bit due to now having a lower octane rating (evaporation)

Best to use it in the car or lawn mower ect and use new.

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""According to Shell Australia’s Technical Advice Centre Manager, Warren Scott, you can generally store fuel in a sealed container for around six months before it starts to deteriorate. This assumes it’s kept relatively cool and away from direct sunlight.

“But if the container is not properly sealed or it’s repeatedly opened, [fuel] will start to evaporate and you lose some of the light components in the fuel,” Mr Warren says.

Those light components include highly important butane. As these components are lost, the fuel loses its volatility. Mr Warren says this makes the car difficult to start.

In warm conditions, fuel is especially prone to oxidisation which causes lacquer and gums to form. As a result, the fuel turns dark in colour, loses its clarity and smells like paint stripper.

Gary Whitfield, Senior Fuel Chemist at BP Australia, says that in the right conditions, fuel can last up to 12 months. But once the container is opened, the fuel will start to degrade.

“Once the seal is broken, a vapour space is formed in the container and the fuel will start to deteriorate more rapidly,” he says.

Okay, so what about fuel that’s left in your car’s tank for a long period of time?

Mr Whitfield claims fuel in a car’s tank can last for up to four weeks before it becomes considerably denser. When this happens, the engine is effectively over-fuelled (without any change in injector pulse-width) and there’s an increased chance of carbon deposition onto spark plugs and inside the combustion chamber. This can cause driveability problems such as stutters and misses.

“Regular unleaded fuel will lose a small amount of octane over time but in our low-sulphur and high detergent Ultimate fuel it might increase very slightly. It might increase 1 RON in four weeks – but it’s not something I’d bother chasing,” he says.

“Keep in mind that typical variation in BP Ultimate is 98 – 100 RON while normal unleaded ranges between 91 – 93 RON.”

Mr Warren says that in most cases, it’s only when fuel is left in the tank for several months there’s the risk of engine damage. This is much more likely to occur in cars running dual LPG/petrol systems.

“By this time the fuel will have gone dark and gummy and can clag the fuel pump, filter and injectors,” Mr Warren says. It can also leave a lacquer deposit on the inside of the fuel tank which is difficult to remove.

In addition, it’s important to be aware that fuel brews – specifically fuel volatility - varies on a month to month basis. Standards vary from state to state but, generally, volatility is reduced during summer months to reduce evaporative emissions. Mr Whitfield says this typically makes the engine slightly harder to start but there is no change in octane.

Lachlan Riddel, proprietor of Gold Coast based tuning company ChipTorque, frequently dyno tests cars which have not previously been driven for several weeks.

“On the fuel mix we have in Queensland, I think fuel in a car’s tank is starting to go off in around three weeks,” Mr Riddel says. “We can tune a car, put it away for three of four weeks, come back to it and it will be either closer to detonation or less likely to make the same power.

“I think local fuel is brewed to reduce evaporative emissions in warm weather and, maybe because of that, fuel really goes crappy in eight to ten weeks. By that stage, the fuel is extremely prone to detonation.”

Interestingly, Mr Riddel hasn’t noticed the engine becoming harder to start but the effect on octane is pronounced.

Similarly, the General Manager of Melbourne’s Advanced Vehicle Operations, Steve Coates, believes fuel tends to go off in a car’s fuel tank quite quickly once it’s a couple of weeks old.

“After a couple of weeks not driving a car, I find that it will be closer to detonation than it was at the time of tuning on the chassis dyno,” he says.

“And the brand of fuel seems to make a difference as well – I find that Mobil and BP products are probably the best after being stored but Shell Optimax is really good when it’s new."

Clearly, there are some important factors to keep in mind when storing fuel in a container for several months or when parking your car for a few weeks.""

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I read somewhere that the 2 stroke oil can break down and loose some of it's ability to lubricate, therefor making seizure more likely. That's why I dont use fuel older than a month since mixed. I dont worry quite as much about lost performance cos my thing needs taming down a bit anyhow ! LOL. Pete x ? !


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What I always do is mix up about 6 ltrs of fresh and add a Ltr or 2 if the older fuel in the fresh mix to use it up. I have got about 6 ltrs of fuel that is a couple of months old now which I will use up by adding a bit at a time to a fresh bach and giving it a good shake before starting the engine.

When I had a solo 210 on a hanglider I often used the same fuel after many months of standing and never noticed a difference. Not kept in an airtight contaioner either.

Who knows.


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Hi Dave.

I think the solo 210 and the simonini are not a great deal different, ie same stable so to speak.

How busy are you in January? I have a fair amount of time off and hope to do some Dartmoor flying over the coming weeks. In the snow with a bit of luck. I will give you a call on the off chance.

Speak soon and hope you have had a good one.


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Good plan.

Base camp among stunning scenery to explore in our magic chairs,, perhaps pub food and beer followed by camp fire and sing along amidst a healthy amount of taking the mickey out of the days events. Get the year off to a good start.

Anyone for the France expedition will find this gathering usefull, Looking at the plans to date, offering input / ideas, clearing any concerns or expectations.

As one of the most successfull tactitions in history Lord H Nelson; he would gather all the officers from his battle group to an evening in his wardroom and listen to all the advice from others who had collectively ammassed a massive ammount of battle experience. From information given by his team and the relevant situation, he would orchestrate his battle plan which more often succeed. (not incluiding the loss of eye, limbs and life of course)

This is what I believe we should do. Find out what exactly people are wanting / expecting from the France trip so we can make a realistic plan. Just for the record, fingers crossed I hope to fly the whole route with exception to the section prior to the home streight.

I have just emtied my whisky glass and must leave you now so I can re-fill it.

Had a nice hour up today and looking forward to a new year day flight. start the year how i plan to go on.

Best wishes for you all and hope to share some sky with you 2010. XX

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As luck would have it I have a good belt of January off as well. Assuming the dates work out well I would like to come along please.

well as you said Please you can come :D

If all works out and I can make it I will be ground crew for you all

(I should be there anyway shouldn't I )

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Just thought I'd take my last look for the year.

Whitters me ol mate. Spare room is made up. Gloves are on charge. Found another bottle of 2 T and the jerry can is in the car to be filled in the next hour. Flattie is on the button and running good. Wings are in the living room being aired and checked........... Ready when you are and Norman, Simon and whoever. Good big sofa , blow up bed etc

Just give 24 hours notice

HNYear all and fly safe


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