Dear Tom and Ray:

My car-knowledge-challenged son lives in North Conway, N.H. His job is about 300 yards from his apartment. Instead of walking, he starts his car every day and drives the three minutes to work. I told him that this is bad for his new Subaru Impreza. He was not impressed. He insists that it is better to start the car every day than to let it sit in the cold weather. Please help me educate this ingrate who does not appreciate his father's vast knowledge. -- Barney

TOM: I feel your pain, Barney. Sure, it's not good for a car to drive 300 yards a day, or even 600 yards, if you count the round trip. When you do that, several things happen.

RAY: First, the car runs inefficiently until it's fully warmed up. When it's warming up, extra gasoline is being sent into the cylinders. But not all of that gas gets combusted. So some of it sneaks down past the rings and dilutes the oil.

TOM: Gasoline is not as good a lubricant as oil. Trust me. I've tried it in my brother's car.

RAY: The other problem is that the exhaust is full of moisture. Actually, it's always full of moisture. But it's only when the exhaust system reaches its full operating temperature that the system can evaporate that moisture and expel it. When you drive just 300 yards, the moisture just sits there and leads to premature rusting of the muffler and the exhaust pipes.

TOM: While he can help the engine a little bit by driving it more extensively on weekends and getting everything up to full operating temperature to expel the moisture and gasoline from the crankcase, he can't reverse the damage he'll be doing all week. So there's no question that the car won't last as long, and will cost him more to maintain, if he drives it very short distances every day. And conversely, there's absolutely no harm in letting it sit during the week.

RAY: Of course, cars exist for our pleasure and convenience. And if he wants to use the car that way, and wants to spend the money on more-frequent oil changes and exhaust systems, that's his prerogative, isn't it, Barney? It certainly keeps us in business.

TOM: But if he is concerned about the cost and the longevity of the car, then you're absolutely right, Barney. He should walk. Plus, it's healthier. Remind him it's better for HIS crankcase and exhaust system, too!