Technical > Automotive > Ethanol in gasoline

reply to Jim Gurd

Re: Ethanol in gasoline

Yes, that's correct. I believe conventional gasoline has a RVP of 9.0 (and higher than that in the winter to allow easier starting in cold weather). Adding even a small percentage of ethanol causes the RVP to rise significantly.

One advantage of low RVP gasoline is that it reduces the chances of getting vapor lock in hot weather. It is less volatile and evaporates much more slowly (and therefore pollutes less from evaporative losses). In the winter the RVP must be increased in order for the gasoline to vaporize properly so you can get the engine started.

One interesting thing I read was that gas companies must run their tanks to almost dry before switching over to low RVP gas. Even a small amount of regular in the tank will cause the low RVP fuel to lose its low RVP properties. They run them virtually dry before making the changeover. This is one reason for price spikes during the conversion from winter gasoline to summer gasoline.
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Here is a map of the boutique fuel requirements nationwide.

»www.mobil.com/USA-English/GFM/Fi···_Map.pdf