Dear Tom and Ray:
A friend of mine says that the speedometers on American-made cars are set 5 mph under the actual speed the vehicle is traveling. For example, if she is driving 60 mph according to the speedometer, she is really only going 55 mph. Foreign cars, however, according to her, are set correctly and show the actual speed the car is going. I find this hard to believe. Is she right? - NancyTOM: Nancy, your friend is wacko.
RAY: I can speak from personal experience about the accuracy of American car speedometers - having been stopped by the state police in 41 of the 50 states. My experience is that they're accurate to within about a mile an hour. When they stop me for doing 72, I'm usually doing 72.
TOM: Of course, that's not what he tells the trooper.
RAY: Oh no. I always remind him that it's a well-known fact that American car speedometers are off by 10 mph, so I was really only doing 62!
Dear Tom and Ray:
Last December, I bought a 1987 Dodge Caravan LE. The van has a four-cylinder Mitsubishi engine with 92,000 miles. The van operates fine on short, local trips and usually quite well on longer trips. However, on two long trips when it was very cold (below 20 degrees), the van suddenly lost power after being on the highway for about 50 or 60 miles. I had to pull off the road, put it in Neutral, let it idle, then it operated normally for a few more miles, then lost power again.
The van was "scoped," and nothing unusual was found. Belts and spark plug wires were changed, and then the same thing happened on another trip! When the van loses power, no indicator lights come on. I have plenty of gas in the tank. There is no serious chugging, just less and less of a response when I step on the gas. Any idea what it could be? - Bruce
RAY: It's carburetor icing, Bruce - something you won't find at your local bakery.
TOM: Under the right conditions - i.e. cold and wet - the air being drawn into the carburetor actually freezes as it passes through. And as the frost builds up around the throat of the carburetor, the opening (where gas and air come in) gets smaller and smaller. Eventually, the opening gets so small that nothing can get through, and the car stops running.
RAY: When you pull over and stop drawing in all that cold, wet air, the ambient heat under the hood melts the ice. Then the carburetor is OK, until you drive a few miles and it ices up again.
TOM: So why is it doing this? It rarely happened on older cars, because older cars sucked air from inside the engine compartment, where it was warm. Modern cars use outside air, because outside air is denser, and dense air is better for combustion.
RAY: To compensate for the colder temperature, the outside air is supposed to be warmed up by a thermostatically controlled "blend door," which mixes some warm, under-the-hood air with that cold outside air. My guess is your "blend door" is stuck or otherwise malfunctioning.
TOM: Have your mechanic check it out and fix it, Bruce. And save your icing for birthday cakes.