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If a plane hasn't flown in several months, is there any concern about flying with fuel that's already in the tank? Aside from the obvious like water or critters in the sump, is there a time when an ounce of avgas burns at an unacceptably lower level of combustibility resulting in an unsafe condition such as dangerously low rate of climb etc.?
Fuel in tank is about a year old; last flew in February, has taxi'd a time or two. Still develops the normal range of max static RPM.
Not going to be a problem. Avgas has stabilizers in it to keep it from gumming up in short term. Several months is nothing. A year probably is still OK.
I've always heard even a year in the tank is no problem for 100LL. Of course do all the checks for moisture and such.
Just to ease the mind some too, I'd do an extended ground run up.
There are other things I'd be worried about before I worried about the gas in a plane that sat. The oil is almost certainly going to need to be changed. If it is a carb'd plane, any fuel that was left in it may have induced some varnish even with the stabilizers. Any rubber diaphrams/seals in pressure carbs and hoses are likely suspect as well.
Clarification, please. None of the gas in your tank is autofuel? All 100LL?Quote:
Originally Posted by CarlOrton
Sounds like me, Carl. Sensible questions, not sure where to find hard data. In absence of data; knowing that "an extended ground runup" means different things to different people; knowing a friend burned up his aircooled Rotax 912 with multiple "extended" ground runups being overly meticulous; knowing my engine (lyc O320) does not need 100 octane; my solution was to drain tank, mix the old 100LL 50/50 with fresh 100LL, and refill through Mr Funnel. Not scientific, maybe riskily experimental.
Lots of people told me that was overkill, avgas is good for several years. Didn't care, that's worked for me. Later I found out a specification requirement is that 100LL not degrade from spec within two years. Some knowledgeable people recommend cutting that period in half, but I haven't found test nor specification data to support that. Here's a sample of some hard data:
http://www.varaceair.com/products.do?item_id=15949
http://www.obr.pl/files/oferta_n/ben...100LL%20en.pdf
http://www.avgas.pl/files/What%20is%...of%20avgas.pdf
your mileage may vary.
I have run avgas as much as 4 yrs old without any problems. When possible, I'll try to "freshen" it, like cdr described by mixing in some fresh avgas. But the ratio is more like 10-15%, or whatever capacity is available in the tank(s).
I do the same thing with my boat and other gasoline powered equipment using autofuel that sit for long periods. Almost everything I own has an inline fuel shutoff valve and I try to run all the fuel out of the carb when shutting it down. This a.m., my generator started on the second pull on autofuel that is over 1 yr old and it's been running fine for about 7 hrs now.
Freshening is a myth. While old gas does lose a little octane and diluting it with new fuel will counter that a bit, this does nothing to quell the gum/varnish that has precipitated out of the fuel.
No claims here that freshening makes a positive change in the fuel's chemical composition. But it does wonders for the psyche and having confidence in the equipment. Just doesn't work as good unless you believe.....
Yes, sir, and data to support that was in one of the fuel industry sources I found somewhere. It said the octane rating, either avgas or autofuel, isn't affected more than a point or two if left in the tank up to four years. Store it in a sealed container under nitrogen not oxygen and it lasts even better. And you're also absolutely right about the gum/varnish problem, which isn't nearly so bad with avgas as with autofuel. So Marty's point is relevant there, freshening works much better if we believe it does.Quote:
Originally Posted by FlyingRon
I've found that Bing carbs have wire semicircles which hold the bowls on so they may be easily removed and dumped before storage; Marvel carbs have drain plugs to empty the bowl; ditto the carb on my Onan generator. They were always too inconvenient to use, until couple years ago when I didn't follow the recommendations in the Onan manual and it went 14 months between operations. Onan book said replace the carb. Too stubborn & too cheap - er, frugal. After fixing that, it's no longer too much trouble to drain the float bowls on anything I own. Just in case shutting off the fuel won't completely drain the bowl.
All of this is sorta common sense after thinking about it. When was the last time the FBO storage tank or fuel truck was absolutely completely empty before refilling?
your mileage may vary