Question: I have a Nissan Stanza with 32,000 miles on it. The car vibrates, mainly in the steering wheel, when I stop. My mechanic told me the carburetor casing is cracked and that it would cost $612 to replace the entire carburetor. How long can I run this car with a defective carburetor?--E.N.
Answer: If the carburetor is defective and the car is registered in California, you might be in luck. Cars sold in this state carry limited 50,000-mile warranties that apply to many of the parts on a carburetor.
Before you go into extensive and costly repairs, you should be convinced that you have identified the actual problem. An old mechanic's trick for checking a cracked carburetor body--a trick that is still useful even in complicated modern engines--could settle the question.
It involves spraying carburetor cleaner around the base of the carburetor. If there is a crack that is leaking air into the system, it will suck in the cleaner mist and usually correct the bad idle condition or the shaking.
Engine shaking and vibration generally is a worse problem in today's cars, such as the Stanza, because engines are mounted transversely and transmit more of their vibration to the car body. In addition, many small cars have four-cylinder engines that idle rougher by nature than six- or eight-cylinder cars.
If the carburetor does have a crack, you should have it fixed. The shaking is probably caused by a too-lean condition that could cause localized overheating in the engine. The car is going to perform poorly, and gas economy is going to be hurt.
Finally, if you do need a new carburetor, you should consider shopping around for a better deal than the $612 you were quoted. It is an outrageous amount of money. Although Nissan recommends prices on parts, Nissan dealers are free to charge whatever they want.
Q: I own a 1974 Volkswagen Beetle. My odometer doesn't register mileage. However, the speedometer is functioning. What seems to be wrong?--B.S.
A: The speedometer and odometer both operate off the same drive cable, which runs from the transmission to the dashboard. The rotating cable drives a series of mechanical gears that register speed and turn the cylinders on the odometer.
Most likely the gears that turn those cylinders are worn out, and the entire mechanism will have to be replaced. On old Volkswagens the job is much easier than on newer cars because the dashboard is accessible from the trunk, which is in front.
Q: A friend told me that I should add a few pounds of pressure in my tires in the summer to keep them cooler. Is he correct?--W.T.
A: Your friend has it backward. Tire pressure increases when the weather turns warmer, about one pound per square inch for each 10 degrees. So a car that is correctly inflated at 40 degrees could be five pounds too high at 90 degrees. By adding a few pounds, you'd be even more overinflated.
What he may have been thinking of is an old and now outdated practice of adding a few pounds of pressure to tires when setting out on a long highway drive. The theory was that it would reduce the tire's footprint and keep it cooler. But tires have been vastly improved, and this is no longer a valid practice.
Tire pressure should be checked regularly. Check when tires are cold, usually in the morning and after the car has been driven less than a mile.
Ralph Vartabedian cannot answer mail personally but will respond in this column to automotive questions of general interest. Do not telephone. Write to Your Wheels, You section, The Times, Times Mirror Square, Los Angeles 90053.