Vapor Lock in Late Model Cars

Twenty cars of the model years 1978 to 1982 were tested for their vapor lock characteristics using the CRC Vapor Lock Procedures. These cars represent the more popular combinations of models/engines for the included years. The tests were run at 70F, 85F, and 100F to cover the normal range of maximum temperatures at which vapor lock problems occur. The gasoline blends used in the test program were also compositionally varied to include both fuels pressurized by butane and those pressurized by isopentane.

Results of this study show late model cars generally to be more able to handle hot fuels without experiencing vapor lock than vehicles of the mid-1960s, the latest vehicles for which comparable data were available. The results also suggest that some revision to the volatility classes in ASTM D-439 Standard Specification for Automotive Gasoline should be considered. In particular, the large jumps in volatility at different ambient temperatures allowed under ASTM D-439 do not match the changes in fleet vapor lock sensitivity to ambient temperature. Additional volatility classes would allow a better matching of fuels to vehicle needs.