Does anyone know how long it takes for gas to go bad and the effects of it on an engine?

 

If you can find our good friend Daniel B Martin, you'll also find the answer.

 

Well, my family has a conversion van that we don't drive very much anymore. It's parked in our garage for like half a year and then driven just to help me and my brother move stuff up to school. I tell my dad to put in some gas stabilizer but he never bothered with that.

So I know that gas is still good after six months. The van (GMC Vandura 2500) starts up PERFECTLY...even better than my Maxima each time. What we do is crank the engine but not start it. I figure that gets the oil flowing but doesn't rev it high like over 1000 RPM. So, when we do start the engine, it is already "prelubricated." For a van that we drive like twice a year, I am surprised how well the engine has held up just sitting there. It's the standard Chevy 350 (5.7L V8), before all that Vortech stuff. Recently we had it smogged. I told my pops to drive it around and get the engine good and hot and burn off all the junk inside it, but once again he didn't do that (my dad never listens to me when it comes to cars). So, with a cold engine (which hasn't been started in six months), six month old gas, and oil that hasn't been changed in God knows when, the van still passed with flying colors, not even exceeding 10% of the maximum allowed.

 

The answer to this question is "it all depends". It depends on the blend (summer vs winter) of the fuel and the container in which it is stored.

Gasoline is a mixture of many similar hydrocarbon compounds. The lighter fractions of the petroleum distillation process are more volatile (that is, more able to evaporate at any particular temperature and atmospheric pressure). The volatile components in gasoline help the engine to start. Oil companies adjust the blend of gasoline to suit the season. They use more volatiles in the winter blend, and less in the summer blend.

The principal way old gasoline turns "bad" is that most of the volatiles have evaporated. This changes the gasoline into something closer to kerosene. Have you ever tried to set fire to a container of kerosene? It's difficult to do, even with a match.

You may wonder why the oil companies don't supply winter blend all year 'round. (1) It's more expensive. (2) It aggravates our air pollution problems. (3) It would make vapor lock more common in the summer months because winter blend has a lower boiling point.

Anyone who is interested in learning more about gasoline's tendency to evaporate will want to read about Reid Vapor Pressure. See
http://www.bre.com/papers/rvp_estimate/rvp_estimate.htm
and
http://pump.net/liquiddata/vaporpressgasolines.htm

For more information about the air pollution problems associated with evaporation of gasoline, see
http://www.hartenergynetwork.com/mot.../reg/morvp.htm
and
http://www.epa.gov/docs/fedrgstr/EPA.../pr-23321.html

The container in which the fuel is stored has an effect because an air-tight container will not allow the volatiles to be lost. Many of us will encounter "bad gas" on a warm spring day when we try to fire up the lawnmower for the first time in the mowing season. Lawnmower gas tanks typically have a vented fuel cap. During the winter layover the volatiles evaporated and escaped through that vent. You can pull that starter rope until you are blue in the face and the blasted Briggs & Stratton won't even cough. I recommend addition of a fuel stabilizer such as Sta-Bil to the lawnmower gas tank at the end of the mowing season to avoid this problem.

Eric's family van starts reliably because it has a vacuum/pressure fuel cap vent. This drastically reduces the amount of losses due to evaporation.


Returning to the original questions...
Q1) How long does it take for gasoline to go bad?
A1) Gasoline stored in an air-tight container will stay good for years. If you are storing winter blend, it will stay good for longer than if you are storing summer blend because you are starting out with more volatiles.

Q2) What is the effect of "bad" gas on an engine?
A2) That depends on how "bad" it has become. If some of the volatiles have been lost, the engine will be difficult to start. If most of the volatiles have been lost, the engine flat-out won't start. However, I don't believe that using old gasoline will result in any lasting damage to the engine.

 

I thought you ate something real bad.