Volatility is the tendency for a liquid to evaporate and is therefore dependent upon its boiling point. A more volatile liquid will have a lower boiling point.

A more volatile flammable liquid will ignite more readily than a less volatile flammable liquid, but I see this is being due to the fact that the fumes are the site of ignition.

Higher octane hydrocarbon fuels tend to be more highly branched aliphatics, which generally does mean higher boiling point. So they can be less volatile. However, much of the octane boosting today is done with additives, like MTBE. Some of these may raise the boiling point (tetraethyl lead probably would), but I would think MTBE, being an ether, would not.

I point this out because it has been mentioned in this thread that cheaper and therefore more volatile fuels may be responsible for his problem. The problem doesn't sound like vapor lock to me, however. But if this were the case, simply changing to a higher octane fuel may not address the issue. Oil companies tend to change their formulations for hot weather, raising the boiling point. If you have gas that is actually a winter blend that an oil company is trying to get rid of, both their high and low octane fomulations probably have a higher volatility, so you need to get your gas from another company if you are having a vapor lock problem, not switch to a high octane formulation from the same company.

posted by 69.130.19...

• Car runs like cr*p, need help (long), epwvt, Tue, 18 Jul 2006 02:41:03
  • You should NEVER run 87 in an Aero...., David Ingram, Tue, 18 Jul 2006 07:40:22
  • Re: Car runs like cr*p, need help (long), chuck kusiak, Tue, 18 Jul 2006 07:00:57
  • maybe a solution, epwvt, Tue, 18 Jul 2006 05:25:55
    • Re: maybe a solution, epwvt, Wed, 19 Jul 2006 05:38:25
      • When did you last change the fuel filter?, EricG, Wed, 19 Jul 2006 13:53:24
        • Re: When did you last change the fuel filter?, epwvt, Thu, 20 Jul 2006 05:36:44
    • Re: maybe a solution, JonAero1, Tue, 18 Jul 2006 08:04:10
      • Re: maybe a solution, TML , Tue, 18 Jul 2006 09:26:53
      • There have been confirmed reports..., David Ingram, Tue, 18 Jul 2006 08:14:47
        • Addendum...., David Ingram, Tue, 18 Jul 2006 08:17:27
          • Re: Addendum...., TML , Tue, 18 Jul 2006 09:29:37
            • The owner's manual says..., soneway, Wed, 19 Jul 2006 17:38:55
              • Autobox=87, confirmed, David Ingram, Wed, 19 Jul 2006 19:37:53
          • Yes, the manual and the sticker inside the gas door...., TKC, Tue, 18 Jul 2006 08:24:45
            • Re: Yes, the manual and the sticker inside the gas door, epwvt, Tue, 18 Jul 2006 08:29:41
              • Automatics have the CSE engine...., David Ingram, Tue, 18 Jul 2006 08:44:28
                • Re: FPT knock, BobS, Tue, 18 Jul 2006 10:43:13
                  • Re: FPT knock, Bill Davies, Tue, 18 Jul 2006 12:50:15
                    • Low RPM low load knock, BobS, Tue, 18 Jul 2006 19:27:26
                • Re: Automatics have the CSE engine...., 951Freak, Tue, 18 Jul 2006 09:42:51
                  • Octane=resistance to burning...., David Ingram, Tue, 18 Jul 2006 11:25:39
                    • volatility is probably a separate issue (long), Erik919kt, Wed, 19 Jul 2006 10:50:34 <-- Viewing This Message
                      • Thanks, I got that wrong...., David Ingram, Wed, 19 Jul 2006 12:59:50
                    • Re: Octane=resistance to burning...., Noel, Tue, 18 Jul 2006 15:05:43
                    • Re: Octane=resistance to burning...., JonAero1, Tue, 18 Jul 2006 11:39:27
                      • Automatic?, David Ingram, Tue, 18 Jul 2006 11:51:28
                        • Re: Automatic?, epwvt, Tue, 18 Jul 2006 12:54:25

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