Propylene glycol (PG) is gaining acceptance as a viable base fluid in engine coolant applications. PG formulations are currently available which rival the performance of those based on ethylene glycol (EG) and have the advantage of being safer products. However, concerns have been raised that because of its higher viscosity, PG might impair vehicle operation in cold weather. This paper examines the low temperature performance of PG base coolants as compared to those based on EG using a combination of laboratory bench scale and actual vehicle testing. No measurable differences were observed between the coolants at temperatures as low as -40°C.