When I was filling up the lawn mower, I spilt some (unleaded) petrol onto concrete.
It came out of a sealed container.
A week later, the big dark stain is still there, still sticky. It's obviously some kind of nasty muck which did not evaporate.
The obvious question is: do you want this in your aircraft fuel system, and the engine?
Even if it is "approved" for Mogas!
How come this is not apparently an issue in practice?
With Avgas, there would be nothing left seconds later. The stuff seems to leave no residue and is often used for degreasing before small paint touch-up work.
It is true that Mogas does leave stains if you e.g. spill it over the wing while refueling. That doesn't mean it contains "nasty muck" that would sit in your fuel system and engine. The stuff that doesn't evaporate is in a solution so as long as there is Mogas (or any other carbon hydrate), there isn't anything nasty. You clean those stains with -- you've guessed it -- fuel!
Avgas on the other hand contains TEL which is the mother of "nasty muck". I don't want this to sit down in my engine which it does. On top of that it harms the environment. Personally I would be against banning leaded Avgas (if done in Europe and in the US so that there is incentive to come up with a sensible replacement).
I've converted my C172M from Avgas to 100% Mogas in 2009 and after a few annuals and 100h, there is a clear pattern of better compression and better spark plug life without any noticeable downsides (except the stains from fuel spills). On top of that, I currently pay € 1.88/l for Mogas whereas Avgas costs € 2.57.
The stuff that doesn't evaporate is in a solution so as long as there is Mogas (or any other carbon hydrate)
However, the stains must form inside the fuel system anywhere where there is no fuel.
One presumably hopes that the incoming fuel will dissolve them.
Mogas has some similarity to a carbonated soft drink - it is a mixture of a lot of liquids with different properties, to achieve a final product with the desired (more or less) characteristics. A chemical compromise. Like a soft drink, not all of it will evaporate from the container, and a yucky residue will be left. Yes, if it does not evaporate, very little residue is left, and the next fuel through will wash it away.
As said, Avgas contains some horrible stuff, which as well as angering some O rings, can really anger low compression engines. The old 80/87 was a "perfect" aviation gasoline, in not containing horrible stuff on either front (other than the red dye residue), but there was not enough market for it, so it's gone.
I have more than 3500 hours flying Mogas in a number of types, and have never had any difficulty with it at all. But, I also care for my fuel system, and use my plane regularly.
Mogas is a problem in infrequently used vehicles - it does tend to "go bad". Avgas keeps much better. Things like motorboats that aren't used daily often end up with varnish in fuel tanks, fittings, carburettors etc. which can result in bad running and engine stoppages. (My dad bought an old boat that had sat for some years, and we had to do a lot of work, including removing the fuel tank, to get all the solid fuel residues that were blocking the fuel filter).
I fly a C172P for years and allways kept in the back side of my brain that something could happen anytime about AvGas.So I obtained an EASA/FAA STC for Mogas .This is a simple documentation for this model ,without any modifications.Kept using Mogas UL100 sporadicaly. LGKO Intl where I'm located, tried the hardest for years to expell the GA from its grounds,first requiring PPR and then responding that its gigantic west apron is full for GA. Eventualy the AvGas operator couldnt survive like this and removed his station 1 year ago ! I dont see any GA in the apron any more and everyone seems happy.Bureaucrats cannot realise what missing revenues from "non all inclusive low cost tourists" harm the island.Such as Taxis,Car Rentals,Hotels,Restaurants,Souvenirs,AvGas VAT,Airport Tax etc.Seems a rocket science to them.They still feel secure and immovable,allthough the general population suffers the most for the 4th year. So,I totaly converted to Mogas 100 with great success.Same performance,lower temperatures,same mileage,50% cheaper than Avgas.2Years,150 hours without any trouble even at 10000 feet.Just stick to the same provider and make random color ,water,and alcohol tests for which I never found anything wrong. Oh..BTW,the PPR NOTAM doesnt exist this year but the dammage has been done./
How do you transport the fuel to the aircraft?
I flew the Jodel rear tank to empty, and the fuel drain was worked on. The engineer put in 10 litres to check the seal. The can he took it from had been sitting unused since December 2016, following the sudden death of its owner. He didn’t know this.
My options are to drain, (slow and difficult) or fill up with 45 litres avgas, and switch to it at a safe height. Front tank is always used for t/off.
Risk of sticking carb bits??
Four year old Avgas, no problem. Four year old Mogas I wouldn’t use in anything including a lawn mower.
As above, I’d drain it out.
There’s a reasonable chance it has got ethanol in it. I’ve noticed on the chainsaws and some garden equipment that can sit for a while that the fuel seems to go off much quicker than it used to.
