Unleaded Fuel. Going 'off' during storage.

[blue up]

I dragged the money pit along to a friendlt farm to have a crack at running the engine. It had been in staorage for 4 months since the last run.
No amount of swinging would get the engine to fire. Normally it goes on the first gentle swing (Leburg ignition) but it refused. After 3 hours, during which my right arm stretched by a good 4 inches, I was about to give up. At this point our friendly farmer suggested squirting a few cc's of neat mogas into one of the pots. Bleedin' thing fired up immediately.
It appears that modern mogas has a storage life of only a few months in a vented fuel tank. Anyone else found this to be a problem? What about Avgas? Any additives worth trying?

Thanks

http://s82.photobucket.com/albums/j279/foggythomas/?action=view&current=CAPN3.jpg

[BristolScout]

I certainly find that my lawn mowers start much more easily after the winter if I put in fresh fuel.

[blue up]

Lawn mower??

I should have mentioned that mine is not a microlight!!:E:E:E






Flame suit on standby...

[Mariner9]

Both Mogas and Avgas will lose volatile components through evaporation in storage.

Mogas will primarily lose Butane, which is a high octane component, thus lowering the octane rating of the fuel. However the cal val of the remaining fuel will actually increase! Neither of these effects would cause any difficulty in starting.

Avgas, having a lower vapour pressure, will lose fewer molecules through evaporation. In addition, the component lost will primarily be pentane, which is a lower octane component, overall having a negligible effect on either the octane rating or cal val of the fuel.

I would say that your problems arose through evaporation of fuel remaining in your carb, leading to gum deposition, blocking fuel flow. The neat mogas in your carbs dissolved the gum and cleared the problem. :8

Edit. Hmmm microlight eh. Was it a 2 stroke engine? If so, add lube oil residues to the gum blocking your carbs :ooh:

[chevvron]

Had a motor bike (4 stroke) filled with unleaded stored in my garage which I hadn't run for over 6 months; no amount of kicking would get it to fire.
When I drained the carb, it was full of a greenish gunge clogging the jets, so I presumed it was the unleaded which had gone off. I would suggest you drain the fuel system and flush it with fresh fuel before flying in case the same thing has happened to you.

[Dan Dare]

Also found the same with my motorbike when its wheeled out after winter. I understand it all gets a bit sticky and not quite so volitile. I can accept that on the bike, but wouldn't really want to use ropey fuel when flying. If you're using a VW, then it shouldn't be too fussy when its actualy running, but I'm not sure I'd take the risk - maybe try 100LL for the last tank of the season next year.

[GOLF_BRAVO_ZULU]

ULGAS also soaks up water like a sponge and that adds to its sludge forming expertise. This has been aggravated by the adulteration of our fuel with ethanol.

That may explain why the "gunge" looks "green"!

[Mariner9]

Sorry GBZ, but thats plain wrong.

Mogas without bioalcohol will not absorb more than a few ppm water - completely irrelevant.

Mogas available in the UK with bioalcohol (not widely available yet but spreading) will not absorb more than 1% water.

The green gunge could have been two things - most likely existant gum or possibly a bacterial contaminant if there was free water present in at the bottom of the tank. (Note,if free water was present, it would not have been there due to absorption)

Edit: On consideration, the gunge could also have included some or all of the "multifunctional additive packages" added to fuel these days for various purposes.

[Tony Hirst]

Not an aeroplane but surely a similar thing. I've had a 924S in the Garage for many years. I wheel out probably at the most twice a year to start it and it always starts first time and then I usually wonder if I'll ever get around to finishing it. Has had the same fuel in it since about 2000.

[The Flying Pram]

I drained some old fuel from a portable generator last week - it had turned a very yellowy colour. Fresh unleaded was virtually clear in comparison.

[blue up]

Yes. The stuff drained off was quite yellow in comparison to the fresh stuff. I wonder if the 928S has the benefit of injection to make it more ..... vapourous (sp?)... whereas the VW that I'm using just gets globs of yellow goo dribbled in that won't turn into fuel/air vapour?
I'll crack the bottom cover off the carb (Stromberg CDS150) and wash it out. I've emptied the rest of the entire fuel system but the carb is close to the bulkhead and not easy to service in situ.

http://s82.photobucket.com/albums/j279/foggythomas/?action=view&current=heatingthemanifolda-1.jpg

[SNS3Guppy]

Several thoughts here.

First, the worst thing you can do to your airplane (short of storing farm animals inside or crashing it) is to let it sit. It's hard on every component in the airplane, and the airplane continues to experience wear and degredation while it sits...more so in fact when acids in oil stay in direct contact with non-moving surfaces, ruby bearings in instruments wear unevenly as the aircraft rocks in the wind in the tie-downs, etc. An airplane should be started and flown at least once a week, if for no other reason that to make it last longer. If you're not flying it, the oil still needs to be changed just like you were...every three to four months even if you never turn a prop...many owners and pilots don't seem to understand this.

Second, mogas/auto fuel is bad for airplanes and system components. Yes, you can get an STC. I was vehemently against the whole program when the EAA was pushing it, and I still marvel that people can be surprised that mogas gums up system components (especially carburetor floats, valves, nozzles, etc), the fuel deteriorates and goes bad, and it can cause deterioration of your rubber and fuel wetted components over time.

If you absolutely must abuse your airplane by letting it sit idle, don't do it with mogas in the tanks or in the carburetor or other fuel components. At a minimum get a mix with avgas, but your best bet is to burn out the auto fuel and replace it with avgas. The aromatics in the avgas preserve your fuel cells and rubber components, and don't leave deposits in your fuel system. I've seen carburetors that needed overhaul just from sitting with mogas in them. Gummed floats and needle valve, sticky components (including in many cases the fuel selector valve), gummed and sticky/leaking sump drains, and so forth.

Auto fuel doesn't have a uniform standard. That is, various refineries use various methods for determining formulation, and numerous additives are put in the fuel which vary depending on who refined it and sold it...to say nothing of what it may have been mixed with in the delivery truck.

Auto fuel has a higher vapor pressure, and is more prone to vapor lock.

From a mechanic's point of view (what you would call an "engineer," I believe), I hate seeing mogas in airplanes. Most other mechanics I know feel the same way. The experimental aircraft association(s) won't tell you this, of course. But for those of us who have had to work on airplanes that are routinely operated on mogas, there's a distinct difference in the condition of the fuel systems. If the airplane is flown regularly and the fuel isnt' allowed to sit, and there's a stringent fuel quality control program in place by the aircraft owner (hard to do), you can get by. But occasional flying, every few months, without any idea of the formulation in the particular batch with which it was last fueled...is asking for trouble.

So far as your 1% potential for hygroscopic action of the fuel (retaining or absorbing moisture), don't forget that the auto fuel may contain more than just a little entrained fuel which is held in suspension or soloution by additives. Handling and quality control on mogas isn't nearly what it is for avgas, and the potential for contamination is substantially higher with mogas.

Most likely nobody is going to change your mind; the price of the fuel speaks much louder to most folks than wisdom or safety. At a minimum, don't go leaving that mogas in your tanks, and don't abuse your airplane by letting it sit idle for so long. It will cost you a much higher price in the end.

[blue up]

I appreciate what you are saying. In an ideal world I would fly every week and traverse the country from one side to the other but the reality of UK flying is that, especially here in Wales (size 8012 square miles, less than New Jersey) there is only one international airport plus a few condemned WW2 strips threatened with destruction or closure plus fuel at a price that would even make the US government whince. £1.10 per UK gallon for Mogas. What is that? $5 per US gallon? Factor in the cost of AVgas over MOgas and you can see why everyone wants to go flying elsewhere. Fields will cost upwards of £9000 per acre, due to the number of 'horsey' people buying up grass for ponies etc. Nearest strip to me is about one hour away.
One hour in the local "PA28" would be £120 ($230 US?) Add on the instructor cost for a check-out and you have the equivalent of the cost of a weeks' wages for most people.
That fuel that I drained out of my tank hasn't gone to waste. My Morris Minor is happy to run on that stuff and it even got a mix of petrol/diesel last year for about 2 months!!!

I've flown in the US many times in the past (even displayed at Oshkosh in 1989). Fantastic flying in open skies. Marvelous ramp personnel, affordable prices and enthusiasm from everyone involved. I just wish you hadn't declared Independence so that I could emigrate more easily!!:E

[SNS3Guppy]

I just wish you hadn't declared Independence so that I could emigrate more easily!!


You're always welcome to stop in.

We didn't exactly declare independence, of course; we defeated an oppressive government to create a free state...otherwise we'd be in the same boat right now, so to speak. Personally, I like free airspace, and I like my concealed firearms.

[A and C]

During the time that I was getting the money together for the ATPL I worked for a local motorcycle shop.

Each spring he had a nice little windfall when just as soon as the weather started to get walm he had a flood of "my bike won't start" calls. 99% of these only needed fresh fuel but add to this a call out fee and 30min labour and it was a nice little number for very little trouble!