Over the past several years, a number of publications have looked at the correlation of laboratory test methods with the low temperature operability limits for the fuel delivery system used with heavy duty Cummins engines. Cummins, which predominates the North American Heavy Duty market, have what is considered the most severe type of fuel delivery system. The Low Temperature Flow Test (LTFT) has been the test which best correlates with this type of vehicle. In this study, the Cummins M11, Cummins NTC, Detroit Diesel 60S, and Caterpillar 3406C Heavy Duty trucks were evaluated in an All Weather Chassis Dynamometer and the results compared to the LTFT and other laboratory tests to see which test best protects all the vehicles. Historical overnight cooling data was examined to compare with the All Weather Chassis Dynamometer cool down cycle to validate the test protocol.In addition, due to their increasing popularity in the U.S., three light duty trucks/utility vehicles (Dodge RAM, GM Suburban, and Ford E350) were evaluated to determine their severity and to see if current laboratory testing would protect these vehicles.