SUMMARY The Time-Temperature Histories of various fuel system components were measured on 80 vehicles during a three-month period in the Summer of 1968. In this program three test patterns were developed from vehicle pattern data supplied by the Coordinating Research Council. The test vehicles were operated over these patterns in Los Angeles County. The purpose of the program was to characterize the time-temperature profiles of fuel system components during normal vehicle operation. A fuel system configuration survey was made and the test vehicles were selected to represent the maximum number of different fuel system configurations possible. The vehicles were instrumented to measure 16 fuel system temperatures and pressures. Measurements of fuel system time-temperature histories for both trip segments and soak periods were conducted.