Classic Car Club of America


Oregon Region


Technical Articles

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Fuel Volatile and our Classic Cars.

By George Potter


While on the “Oregon Adventure CARavan” I noted a problem that many of the CARavaners  were experiencing or worried about “Vapor lock”.  Most were convinced that the high volatility of the fuel was a result of E10 (Ethanol fuel) and were looking for (Clear Gas Non- Ethanol fuel) stations. One of the tour participants commented that he used only premium fuel as it had less volatiles.


Hmm all sounded interesting and being one of those who wants to know for sure I decided to do a Google search. My search “is premium gas less volatile”. Wow pages full of answers, all saying yes premium was indeed less volatile and a lot of other information concerning our modern fuels.


The articles all agreed that the higher the octane rating on fuel the less volatiles (evaporative qualities) it has and to us that means less vapor lock. The engine runs best with a slow even burning of the fuel. Octane ratings are an indication of the burn or flash rate of fuel. The higher the octane rating the lower the volatiles and the slower it burns. Now it makes sense to me, high octane fuel has fewer volatiles to slow the burn rate and fewer volatiles means less vapor lock.


There’s lots of information attesting to the bad side effects of E10 fuel when used in our old cars. A couple of reasons for avoiding it is that it is an excellent absorber of water that then condenses out in our tanks and fuel system.  It is a solvent that damages gaskets and any rubber parts in our fuel systems. Interestingly I could not find any information indicating that adding Ethanol actually increased fuel volatility.


So my conclusion, the CARavaners were correct in using Clear Gas or Premium fuel. Clear Gas has to be the first choice because Clear Gas is high octane and non-ethanol thereby reducing vapor lock and the damaging effects of Ethanol. If Clear Gas is not available the next best option is high octane premium fuel.


 Here are some on the other highlights of my fuels search:

  • ·         "PREMIUM." The logic is that since it is a premium fuel it must be better. In reality, the premium label originates from the higher cost to refine and the resultant higher retail cost. It is reasonable to assume that premium fuel is the same as high octane fuels.

  • ·         Some owners think that these fuels will make their vehicles more powerful. This is a MYTH! Only engines with high compression ratios, 9.3 or more, can deliver all the potential energy from higher octane fuels! In fact using Premium in low compression engines will result in a slightly reduced HP and MPG,

  • ·         Modern engines, 1990 and later will safely burn 87 octane even with a higher compression ratio. This is accomplished by the engine fuel/air management/timing system in modern cars adjusting so as not to cause pre-detonation (ping) in the engine.

  • ·         The storage life of fuel is one year when stored under shelter in a sealed container. Once a seal is broken the fuel has a storage life of six months at 65 °F, or three months at 85 °F. If stored in an open container or fuel tank, the storage life is reduced to one month. And now we know why we add fuel preserver to our tanks……