Change Oil on Rarely Driven Cars
Question: I am the owner of a 1940 Chevrolet in excellent running condition. The car is driven fewer than 100 miles a year, but I am told that I still need to change the oil at least once a year. But the oil looks as good as new. Is this necessary, and if so, why?--W.F.
Answer: It probably is helpful to change the oil, because with so few miles being put on the car, there is a good chance that the engine does not get hot enough to burn off contaminants in the oil. Moisture and hydrocarbons can build up in oil when the car is used for only short trips, but a long drive gets the engine hot enough to evaporate these problem substances.
The one exception to this advice would be if you put the 100 miles on your car in one long drive, but that is probably not what you do.
If you really object to changing the oil, you might consider using a special preservation oil. One developed for military vehicles that are put into storage is designated Mil L21260-D; it contains special rust inhibitors. You should be able to find it at industrial lubrication distributors in five-gallon cans. The oil is rated at SF, just one notch under the current SG top rating for motor oil. But it would probably be easier just to change your oil once a year.
Q: I own a 1982 Cadillac Fleetwood Brougham with 43,000 miles on it. On a couple of recent trips over the mountains, the car would not go any faster than 45 miles an hour uphill. It would not seem to downshift, either. At times, the check engine light comes on and the on-board computer has indicated we have a condition 39. But the dealer hasn’t found any defects and cannot solve our problem. I had a new torque converter installed in 1987. Is this unique?--N.E.L.
A: As you are probably aware, General Motors cars built in the early 1980s have had numerous automatic transmission problems. A good transmission mechanic, if you can find one, will make your motoring life a lot easier.
Your Cadillac’s automatic transmission has a torque converter lockup system. A torque converter is a type of fluid clutch that allows the engine to be disengaged from the transmission at idle.
The standard torque converter passes power from the engine to the transmission by forcing fluid at high pressure to power a small turbine. On newer cars, a mechanical connection called a lockup is added; this connects the engine to the transmission at cruising speed, which is supposed to help fuel economy.
The lockup mechanism is controlled electronically, based on the speed of the engine, the speed of the car, the temperature and the load on the engine. It should lock up only when you are at constant speed on fairly level terrain.
The condition 39 signaled by your computerized diagnostic system indicates that you have a torque converter problem. Most likely, you have a malfunction in a switch or sensor that tells the converter when to lock. It could be something as simple as a brake light sensor switch that is stuck, because the brake light switch tells the computer when to disengage the lockup mechanism.
You should also be careful not to drive with your foot even lightly on the brake pedal, because this tricks the computer into thinking that you are stopping the car, which in turn disengages the lockup system.
The performance problems you described can perhaps be explained by a malfunction in the lockup system. If the torque converter does not lock properly, then the transmission can overheat and the cooling system can be overburdened trying to cope with the condition. This, in turn, leads to other problems.
