Curiosity Idling High Over Tuneup
Question: I have a 1988 Mazda, which I recently took in for a tuneup. All the mechanic did was change my spark plugs and check the timing. He told me that he could not do anything with the carburetor unless I wanted to pay more for him to crack open the seal. Did I get ripped off or is the mechanic being honest?--M.M.
Answer: Whether you were ripped off depends on how much you paid for your tuneup, but the mechanic was correct that the carburetor adjustment screws are sealed.
You can easily see why garages that advertise so-called bargain tuneups for $40 or $50 are raking in the dough. New cars virtually have nothing to tune up, save for a spark plug change and a possible timing adjustment or valve adjustment.
The carburetor on your Mazda and most new cars have adjustment screws that are sealed at the factory. In most cases, it is illegal for a mechanic to attempt to break open these seals to change the settings. In many other cases, fuel injection systems are controlled by computers that cannot be adjusted.
In the old days, a car would need a carburetor adjustment new spark plugs, points, condenser and a rotor every 12,000 miles. But these are the days of computer-controlled engines. There are no more rotors or condensers.
If you think that means your car is maintenance-free, however, you are mistaken. Not surprisingly, the computers that now control the ignition and fuel systems on cars break on occasion. And when that happens, you can be looking at repairs bills that easily jump over $500. Then you’ll wish you had only a pair of points to replace.
Q: The oil pressure indicator, battery charger indicator, gasoline gauge and clock on my 1982 Datsun King Cab have gone on the blink. Where is the problem?--U.K.W.
A: You have probably tried to determine whether there is a blown fuse in the fuse panel and found no problem there. But in this case, your Datsun has a surprise for you.
There is another fuse behind the dashboard, called an in-line fuse. It’s probably blown, which accounts for all the instruments malfunctioning.
Fuses are designed to prevent overloaded circuits from damaging your car’s electrical system. Fuses usually blow for a reason. Once you find the blown fuse and replace it, the new one could very well blow out too.
That makes the ultimate repair a more challenging problem. You may have to selectively disconnect the various sensors to see which one is creating the electrical overload. At some point, you may need a good electrical mechanic to track down the problem.
Q: Is there any simple way to test that Mobil One was actually used in an oil change, rather than a cheaper oil?--J.R.
A: A petroleum lab could easily tell, but a consumer can not determine that by look, feel or smell. A lab would run a “pour point” test on the oil to determine its low temperature properties, which are notably better with a synthetic like Mobil One than with a mineral-based oil.
You could do a crude test of your own by putting a sample of the oil in the freezer. A mineral oil would be very thick at below freezing but Mobil One should be reasonably fluid. But wouldn’t it be easier to just find a mechanic you trust?
