Cold Weather Driveability Performance of 1975 – 1981 Model Cars 821203

Low and intermediate (25°F and 45°F) temperature controlled driveability tests were conducted with 1975, 1977 and 1981 model year cars. Cold-start and warm-up driveability of the test fleets improved from 1975 to 1977 to 1981. Results of individual car and fuel tests show much greater variation among cars than among fuels. No attempt was made to investigate causes of the large performance differences among cars; the smaller performance differences among fuels were found to be related to changes in the fuels’ 10%, 50% and 90% evaporated temperatures. The 50% evaporated temperature was found to be the most important predictor of fuel performance, with the 10% evaporated temperature being almost equally important. As expected, the results in each of the individual programs also indicate improved average driveability performance with increasing ambient test temperature--about 25% fewer performance problems at 45°F than at 250°F.