Father-in-law is right: Turning off engine at stops can save gas

Q I suppose it goes without saying that any father-in-law seems crazy to the son-in-law, and, perhaps more emphatically, the son-in-law seems crazy to the father-in-law (What? This thing hoodwinked my daughter, etc.?) But let me present a specific case that might tend to push the balance in my favor (I'm the son-in-law).

To cut to the chase: My father-in-law turns off his truck at every stop. Why? My wife tells me that he insists that he is saving gas. Let me further underline the peculiarity of this behavior. We live in Las Cruces, N.M., a town not associated with traffic congestion. You are not likely to sit idling for more than 5 minutes anywhere at anytime probably 95 percent of the time. My question: Is this loony or what? Also, can you give me some scientific explication on the subject, i.e., what's the effect on miles per gallon; effect on the car; is this an inheritable personality defect?

TOM: This is obviously your first marriage. Because by the second or third marriage (take my word for this), every man learns that you should never try to get between your wife and her sainted father.

RAY: Particularly when you happen to be wrong, like YOU are in this case.

TOM: Your father-in-law is doing a good thing for the planet. Idling is a waste of fuel. It increases dependence on foreign oil, pollutes the atmosphere and puts wear and tear on your engine. Not to mention the squeeze it puts on your bank account.

RAY: So turning off the engine when you're going to be sitting for more than a minute or two is a great thing to do. Most hybrid vehicles do this automatically. When you come to a stop, the engine shuts down, and the moment you touch the gas pedal, it instantaneously starts up.

TOM: At least one energy expert we know suggested that if ALL vehicles shut down automatically at idle, we could cut our fuel consumption by 10 percent. Or about 40 MILLION gallons a day!

RAY: Some people are worried about turning off their air conditioner in the summer, or their heater in the winter. But if you leave the fan blower running, there's enough residual hot or cool air to keep the car at a comfortable temperature while you sit there. Even in five minutes, which is much longer than the average person usually idles, the temperature inside the cabin won't change much.

Q. I often want to know in what direction I'm driving. So I'll buy these stick-on-the-dash compasses. They seem OK when outside the vehicle, but when mounted inside and in use, they give directions, at times, that I know are false. Do cars have a magnetic field that interferes with the readings, are the compasses too cheap, is Earth losing its polarity or are you not the right people to ask this?

TOM: All of the above.

RAY: I think scientists have discovered that magnetic north is migrating. And they predict that in about 50,000 years, Earth's poles are going to switch, so the north pole will be at the south pole. But I don't think your car will be around then.

TOM: The biggest source of electromagnetism in your car is your alternator, which is, essentially, a big electromagnet. But I would think that if it was throwing off your compass, it would throw it off all the time. You say "at times" you know the reading is false. Maybe that means at other times it's also false, but you just don't know it.

RAY: Or it could be that as the output of the alternator increases with the speed of the engine, the magnetic interference increases.

TOM: Anytime a current is going through any wire, you're making magnetism. There are lots of wires running behind and under the dashboard. But I'd say it's more likely to be affected by things outside the car, such as overhead power lines.

RAY: So our answers are: Yes, there are sources of magnetism in the car, yes, you're buying cheap compasses, and yes, we are not the right people to ask. If any of our readers have a better answer, drop us a note.

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