Originally Posted by File IFR
I always thought that cold air temps actually improve 'performace' (milage may be different) on an internal combustion engine..... the air is more dense that warm air.
.... True?? Anyone??
Yes, performance does improve with the cold dense air.
Its also pretty normal for milage to bomb with short trips in cold temps - richer mixture and the fact that it will stay in open loop pretty much the entire trip as the coolant temp will barely reach normal by the time its shut off. Combine that with tire pressure dropping off in the cold, cold (stiff) tires, and the stiff, cold gear oil in the diff(s), t-case if a 4x4, and transmission, and 0mpg warm-up time, its a noticable difference. Switching drivetrain fluids to synthetic helps a wee bit. Personally, I've seen a 30%+ increase in fuel consumption with short trips in the cold. A block heater with a timer helps some too, have it come on 3 hours before you're going to start the truck.