Full tank or better to drive about half full?

Is it better to keep the tank topped up to full, or should I drive around on half empty: what's better for my car and fuel consumption? Why might althletes take an ice bath after exercise? If I go out with wet hair, will I really catch a cold, or is that a myth? Do babies sleep better in a cooler room? What's the difference between an electrical blackout and a brownout? Is the expensive face cream better than the cheaper one? Lester Kiewit and Dr Chris have the answers... Like this podcast? Please help us by supporting the Naked Scientists