Dear Tom and Ray:

I am a valet at a local country club in Wisconsin. As you well know, it gets very cold here in the winter months, and that leads to my question. As a favor to the members who choose to valet park with me, I like to warm up their cars before they leave. I let the cars run anywhere from two to 15 minutes, depending on how long they take to get ready to leave, get their coats, finish conversations, etc. So my question is: Am I doing any damage to these automobiles? Would they be better off next winter driving away in ice-cold cars?

- John

RAY: You're not harming their cars, John. The only harm you're doing is wasting gasoline. And since they're all paying exorbitant dues to belong to a country club, they're probably not worried about gas money.

TOM: In the old days, when cars were carbureted, you COULD do harm by warming up a car for too long. In warm-up mode, a carburetor would pour lots of gasoline into the cylinders, and the excess gasoline could run down into the crankcase and dilute the oil. And the rich mixture could ruin the catalytic converter, too.

RAY: But modern cars meter their gasoline into the cylinders so precisely, with the help of computers, that they can idle for days without a problem. This was proven in Princeton University's famous "Police Cars in Front of Dunkin' Donuts" study from 2003. And 2004. And 2005.

TOM: So, in terms of the cars themselves, you're doing no harm. And I'm sure your customers appreciate getting into a warm car and having heat immediately.

RAY: The only other downside is the extra pollution created by these long warm-ups. But I'd deal with that on a case-by-case basis. Now that you know who the good tippers are, John, next winter, make sure THOSE cars get warmed up. And balance out that extra pollution by not warming up the cars of the lousy tippers. In fact, you can turn on their electric seat coolers.