if going a short distance, is it worse in the cold (below zero, it was around -10 this morning) to start the car and let it run a bit, or drive it right away and not let the engine warm up at all by the time it gets shut off again. i'm asking because lately i've been working less than a mile from my house, so neither the trip there, nor the trip back lets the engine heat up much at all. either option doesn't sound optimal, but is one better than the other? thanks