How long does it take gas to go bad?

grandx

Petty Officer 1st Class
Joined
May 21, 2001
Messages
383
Re: How long does it take gas to go bad?

v12, i've seen some claims of such, but I don't believe it. Drain it and dispose of it properly and start with fresh.
 

BillP

Captain
Joined
Aug 10, 2002
Messages
3,290
Re: How long does it take gas to go bad?

nevjb,<br />Let's clarify the airplane storage deal. I'm a pilot and past plane(2)owner so will speak from my own experience. Planes sit for months or years between flights. Yes, fuel is purged in the preflight check and after fueling but it isn't the carb that is purged. The "delivery system" is purged. The carbs never get purged unless it is for problems or repair. <br /><br />I don't know what the gas difference is but you can take any auto down to the airstrip and pump 100LL av fuel into it and drive off. I used to see it every Friday evening with the street drag guys. It will run fine but I suppose eventually clog up the emission system. Otherwise you will just have a peppy engine that runs dirty. <br /><br />N276SP
 

rodbolt

Supreme Mariner
Joined
Sep 1, 2003
Messages
20,066
Re: How long does it take gas to go bad?

hello<br /> as a shop owner I will agree. yall please dont use stabil or anyother product. I really need the money that clogged carbs bring every spring. as far as aviation fuel it will make your outboard or most any other high performance motor actually run slower. I have extensive track and dyno sessions with a 68 camero with a 427 and several customers that race outboards. high octane does not mean its going to go faster and usually means it will go slower. most airplane engines dont turn anywhere near 5000 rpm.<br /> good luck and keep posting :)
 

rons boat

Petty Officer 1st Class
Joined
Dec 28, 2002
Messages
210
Re: How long does it take gas to go bad?

I hope to pass the wisdom of the 1980s when the EAA or Experimental Aircraft got cargas approved for Airplanes. The answer they found is all car gas is not the same. Refiners start with a basic mix which has a natural octane and add airomatics to it to raise the octane. Airomatics boil off with temperature, lack of pressure, and leave the problems behind. Natural octaine gas like used in aviation do not have any problems with life and stay the same for years. Our car gas today is made from bases of lessor quality and is not held to a standard. Only the final mix with the aeromatics added is tested for octane. The reason they are called aeromatics is this octance boosting substance is the smell of car gas and raises the base to the octane required for sale for car use. Aeromatics also are responsible for swelling rubber gaskets and other parts that would affect airplanes. As the abiliity of octanes boosters have gotten better at boosting of poorer bases they have not necessarly been good as enhancing the life of poor quality bases. For people who want the answer, use 100LL avation fuel or even 80 octane no lead if available. 100 Low lead contains 2.5 ML per gal lead which is what all early marine engines were designed for.
 

BillP

Captain
Joined
Aug 10, 2002
Messages
3,290
Re: How long does it take gas to go bad?

rodbolt,<br />I've heard higher octane will run slower but it must not be the norm for 4 strokers. Virtually every car or mcy drag racer from nationals to local uses it. I'm sure setup has everything to do with it.
 

jim dozier

Lieutenant Commander
Joined
Jan 8, 2003
Messages
1,970
Re: How long does it take gas to go bad?

BillP, the reason the street racers use high octane is not because it makes an engine go faster, it is because they have higher compression engines, many of which have been modified to higher compression by the owner, and higher compression engines require higher octane. Some of these guys will retard the ignition so that they can drive the beast to work Mon-Fri on cheaper lower octance car gas. Then on Sat nite they advance the ignition to the best position, put in the higher octance gas (aviation or other) to prevent detonation, and realize a perfomance boost commensurate with their high compression. Octane in excess of the requirement for the particular compression ratio and ignition advance for a given engine will not under any circumstances provide additional power and may in certain circumstances lessen it.
 

BillP

Captain
Joined
Aug 10, 2002
Messages
3,290
Re: How long does it take gas to go bad?

jimd...yep. This is like the stabil thing. I've seen way more non tweaked stock motors use mild 105 drag strip fuel and turn lower ETs than ones who ran stock 92 pump fuel. I think most motors handle higher octane vs ones that don't. I've also seen many outboard motors sit 6-12 months without stabil and have zero problems so believe the Stabil issue is not as bad as advertised. Not even close. Like I already posted...about 30 yrs ago my clogged carb problems stopped when I quit running the carbs dry. Running dry was causing MY problems, not bad fuel. This has repeated itself too many times to be bogus. I am guessing most motors that normally go into the shop for plugged carbs have (1)had the carbs run dry before storage and (2)sat way longer than a "season".
 

kd6nem

Chief Petty Officer
Joined
Jul 25, 2003
Messages
576
Re: How long does it take gas to go bad?

One difference between aviation fuel (avgas) and gasoline is that gasoline has an aromatic base while avgas has a parafin base, chemically. Probably other differences also. I think vapor pressure is lower in avgas making it better for higher altitude flight, more resistant to vapor lock. Gasoline does indeed have more than one kind of hydrocarbon molecule from what I gather, and the ratio changes with the season and octane rating. I'd guess that maybe the longer chains burn a bit slower hence the higher octane rating. Without higher compression and/or more advanced timing higher octane is a waste in most auto engines.
 

rons boat

Petty Officer 1st Class
Joined
Dec 28, 2002
Messages
210
Re: How long does it take gas to go bad?

Bearcat you seem to understand. My friends at the AMCO refinery while working on the AVGAS vs Cargas issue pointed out that the Aeromatics used to boost the octane of the poorer bases of cargas starts coming off very fast and so cargas has a very limited life. Car gas spoils since the aeromatics are unstable and will tend to boil off with lower atmospheric pressure and temperature or even just shaking around. The more smell (aeromatics) the refiner had to use to get the cargas up to standard the more unstable and the shorter the life. While avgas has to be very stable and may remain so with even years of storage and high altitudes it is a quality product dictated by Federal Regultions. Knowledgeable people frequently use 100LL or blue AVGAS in lawn mowers, generators, other tools that sit around. Be careful not to use in engines with Catalaytic Converters since it does contain lead. Octane has nothing to do with anything except the ability not to preignite before the spark. That allows the explosion to be precise and produce explosive power at the the precise time so all energy is placed on the down side of the stroke to the crankshaft. Thus no energy is wasted by preignition. Lead is a wonderful valve lubricator and octane booster. Aviation convinced the goverment that engines designed for lead would have catostrophic failures in the air without it. The only downside to the use of lead as you have to check your sparkplugs slightly more often to remove any possible lead fowling and of course the argument that it causes harm to the environment. Not harmful enough however, to remove it from avgas where the government agrees it is the safest alternative for high reliablity engines like required for aviation. You bet it is in my stored devices and I have never seen it go bad yet. I am a pilot and a boat owner. No stable for me since Avgas doesn't have that smelly aeromatics to start with. Just good natural high octane bases with a little lead.
 
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