Q. Since the most recent snowstorm, my daughter’s Jeep Cherokee has been acting strangely. There is a thumping feeling when the wheel is turned. It is most pronounced in parking lots. Do you think the snow damaged something?
T.W., Ashton, Va.
A. Tell your daughter to take her Jeep out of four-wheel-drive. We have a hunch she selected it for the snow and left it engaged. The condition you feel is called “crow hopping” and is common on 4WD trucks making tight turns on dry pavement.
Q. I frequently encounter those portable radar signs that the police use to warn drivers about their speed. The radar usually says 2-3 m.p.h. less than what my speedometer shows in the 25-30 m.p.h. range. Is the problem with my speedometer or their radar? If it is my speedometer, does this affect the accuracy of the mileage on my odometer?
B.M., Schaumburg
A. We happened to come upon a cop setting up one of these in our town the other day. We thanked him for his efforts to slow the traffic on our road, then posed your question.
The officer told us that the radar in those portable devices is 100 percent accurate and is recalibrated before use. He added that it is so accurate he can write tickets with it.
The problem may be in your speedometer and, if so, will affect your odometer.
Q. You often talk about following the owner’s manual when a maintenance conflict between a dealer and the owner’s manual occurs. But why do you still suggest the three-month or 3,000-mile oil changes when the owner’s manual specifies a higher mileage and timeframe, for example, six months or 7,500 miles? If people just followed the manual, we should save on oil waste.
S.D., Buffalo Grove
A. We have said that you need only follow the schedule in your owner’s manual to keep your warranty in force. Some dealers imply that their schedules are essential.
We do suggest more frequent oil changes as an inexpensive way to prolong your engine’s life. We also suggest brake fluid changes, especially on cars with anti-lock brakes, to prevent valve-assembly problems. We even suggest changing the transmission fluid more often than the book calls for. But we do not say that you must have these services.
The amount of energy needed to make a new engine far exceeds the few extra quarts of oil you consume.
Q. For the last two winters I have noticed a decline in fuel economy. In the late spring, the fuel economy goes back up. Driving habits remain constant. I have been talking with a bunch of people, and the general thought is that reformulated gasoline (winter blend) could be the culprit. If the winter blend is to help reduce pollution in the winter, how valid is it when you wind up having to burn more gas to go the same mileage you do in the summer?
E.H., Glenview
A. If tailpipe emissions are practically nil, burning more fuel should still cause less pollution. What rankles us is that we motorists have to pay while stationary sources such as power plants and factories can continue polluting by trading emissions credits.
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Bob Weber is an ASE-certified Master Automobile Technician, having recertified every five years since 1978. Address your technical questions about cars and trucks to him in care of Motormouth, 17717 Silcott Springs Rd., Purcellville, Va., 20132. Send e-mail, including name and town, to MMTribune@netscape.net. Answers will be supplied only through the newspaper.
