Frankly thats not true in most vehicles. I started a 2000 Ford Probe in @ -38F without an engine block heater after it had sat all night. Its was a near thing, and its not something thats probably good for the engine to do every day.... but you can start a car sub zero wtihout an engine block heater---usually. Its certainly nice to have the reassurace AND to have the oil a bit thinner than molasses when she cranks over though.