Question: I find that some garages, when doing an oil and filter change, will put in as much as one full quart of oil over the full mark on my dip stick. They say it will not harm the engine, but my automotive owner's manual says in big letters: "Don't Overfill." What harm can it do?--J.M.
Answer: You are right to be concerned about how much oil your garage is adding to your crankcase, because at the very least it can cause minor problems in the operation of your engine, and it possibly can do major damage.
Oil is stored at the bottom of an engine in an area called an oil pan, which is designed to hold a certain amount of reserve oil that guarantees the engine an adequate supply in almost any operating condition.
But if the oil reaches too high a level, it can be splashed excessively by the engine's moving parts, particularly the crankshaft. The oil will splash upward and get inside the cylinder, causing oil fouling of the spark plugs. That could cost you a tuneup.
Worse yet, if highly agitated and foamed oil is drawn into the oil pump and distributed through various oil passages, it can cause the formation of air pockets that can starve the upper engine of lubrication, according to technical experts at the Automobile Club of Southern California.
Overfilling is not uncommon because most garages add oil in one-quart quantities, even though manufacturers specify oil capacities in tenths of a quart.
If you think a garage has overfilled your engine, have the oil drained and refill the engine. A shortcut would be to simply remove and drain the oil filter, which holds about a quart of oil.
Q: I own a 1980 Toyota Corolla with an automatic transmission. It is getting poor fuel economy. At least, I think so. In the first year I owned it, the car got 19.4 miles per gallon in all-city driving. Now, it is getting only 17.5 miles. Is that normal?--C.S.
A: No, you should be getting better mileage than 17.5 miles per gallon with your "economy" car and the limited amount of driving you do. In all-city driving and even taking short trips, you should be getting about 20 to 22 miles per gallon.
Normally, fuel economy improves after the first 12,000 miles and then should remain about the same for 50,000 miles or more. With the proper care and maintenance, an engine and transmission should last more than 100,000 miles with only minor loss of power and fuel economy.
The least costly source of the problem might be a dirty air cleaner, which can starve an engine of air and cause it to burn more gasoline. Next, have your mechanic look at the ignition system, including the possibility of dirty spark plugs. You might also have a problem with your choke or carburetor.
Q: My 1974 Plymouth Duster has severe front-end shaking when I drive faster than 50 miles per hour. It seems to lessen somewhat at 60 miles per hour. An alignment and wheel balancing did not seem to help. What should I do next?--E.S.
A: You should have your front end thoroughly checked for any loose parts, such as tie-rod ends, ball joints and steering arms. A loose front end will not stay aligned.
If that checks out, you should have your tires spin-balanced while they are on the car. If the problem remains, possibly a moving part is out of balance, such as your drive shaft.
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.