MadSci Network: Chemistry

Re: What is the boiling point of gasoline under 35 psi?

Date: Thu Aug 12 18:04:13 1999
Posted By: Adrian Popa, Directors Office, Hughes Research Laboratories
Area of science: Chemistry
ID: 934327899.Ch


The boiling point of gasoline need not be reached to have vapor lock, it is 
the Vapor Pressure of the gasoline that is important. There are a number of 
variables in the vapor lock problem. The higher the octane 
of the gasoline, the higher the volatility the greater the chance for vapor 
lock. See the Shell oil information at the following URL: 

The boiling point  ( standard boiling point; normal boiling point) is the 
temperature at which the vapor pressure of a liquid is equal to the 
external pressure on the liquid. The standard boiling point is the 
temperature at which the vapor pressure of a liquid equals standard 

Vapor Pressure for street grade gasoline ranges from 9.0 to 15.0 psi  
(pounds per square inch) depending on the air temperature of the 
environment. Generally, if the gasoline’s vapor pressure is above 8 psi 
vapor lock becomes a problem (see Unocal reference).

The higher the average air temperature of a locale, the lower the Vapor 
Pressure needs to be. The lower the median temperature of an area, the 
higher the Vapor Pressure must be to properly atomize the fuel with air for 
proper engine combustion.

See the Racing Gasoline Frequently Asked Questions which has been compiled 
from documentation by Tim Wusz, Unocal Corporation  and magazine articles 
at the following URL for more detailed information:

To help you understand all these terms there is an excellent General 
Chemistry  reference site on the Web that defines and explains vapor 
pressure, boiling points, standard pressure etc. at the following URL:

Best regards, Your Mad Scientist
Adrian Popa

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