Question: During a recent brake job, I observed a mechanic repacking my wheel bearings by pushing in new grease without first cleaning the bearing. When I asked him about it, he said washing the bearing with a solvent leaves a residue that is harmful. I have never heard of this, and I am wondering if he knew what he was talking about.--K.P.
Answer: Although you did not mention the make and model of your car, almost every auto manufacturer and professional auto-care manual recommends that wheel bearings should be cleaned in a solvent and visually inspected for wear before they are repacked with clean bearing grease.
The correct procedure, however, can double or triple the amount of time it takes to repack a wheel bearing. The bearings, which carry the full load of each wheel, must be carefully washed in a solvent until all the old grease is dissolved. If they are properly dried, they will not retain any harmful residue.
The reason for all this trouble is that the dirty grease contains microscopic particles of metal and other contaminants that can accelerate the wear of a bearing. In addition, a bearing cannot be visually inspected for damage until it is cleaned.
A mechanic who shortcuts this procedure knows that by the time the bearing fails, it will be months, if not years, after the faulty service, and nobody could possibly link the failure to one long-forgotten shortcut. It is in cases like this that the importance of having a conscientious, honest mechanic cannot be minimized.
Q: I brought my 1985 Volkswagen Vanagon to a dealer for the 30,000-mile service. The service cost $350 because the OXS sensor needs replacement at 30,000 miles, I was told. When I got home, I searched the owner's manual for mention of the OXS sensor and found, "Replace and reset OXS SERVICE reminder light." Did I pay $104.95 to reset a light?--M.B.
A: It is unlikely that you paid $104.95 for resetting a light. What you probably received was a new OXS sensor, which is a sensor that determines the oxygen content of the engine exhaust and feeds data to a computer that adjusts the fuel-injection system.
The reminder light comes on to notify you that the realistic service life of the sensor has been reached and that it should be replaced to conform to federal government rules. But dealers cannot force you to replace the sensor, and if you refuse to do so, they will simply reset the reminder light.
Q: I own a 1983 Cutlass Ciera with a diesel engine. I don't remember when it first occurred, but when the fuel tank get below half full the car starts to run rough and then stalls. After I fill it up, it runs perfectly. What do you feel the problem is?--M.D.
A: This has been a problem with some Oldsmobiles. A filter on the pickup tube inside fuel tank has probably become clogged.
The fuel system has a bypass pickup at a higher level in the tank, which allows you to operate the car on more than a half tank of fuel even if the lower pickup tube is clogged. It seems rather disingenuous to put in this feature, however, without telling owners about it in the owner's manual. Diesel fuel is subject to more contamination problems than gasoline. In the past, algae has been found growing inside diesel fuel tanks. You will probably need to have the filter replaced and the gas tank cleaned.