Question: I have owned many cars through the years that had maintenance-free or sealed batteries. I currently have two Fords with such batteries. In every case, these batteries have caps that can be pried off carefully using a small screw driver. I find that they occasionally need distilled water. In this way, a few minutes of my time and a little water has saved me $60 or more for a new battery.--H.W.K.
Answer: The procedure you describe is not recommended by battery manufacturers, who have tried to design and produce batteries that alleviate the chore of keeping the water level up in a battery. Of course, those sealed batteries in many cases do fail for the simple lack of water that careful maintenance could prevent.
Virtually all 12-volt automobile batteries are so-called lead acid batteries, in which plates of lead are immersed in sulfuric acid. The lead and acid create electricity through a chemical reaction, which can be reversed when the car's alternator or generator recharges the battery. Eventually, though, water that is generated in the chemical reaction is lost to evaporation, which causes the plates to be exposed to air and to lose their effectiveness.
Your effort to pry off the caps of the sealed battery is something that some mechanics admit they do on their own batteries, even though for the average motorist it can be unsafe. Battery acid is quite caustic and can burn the skin, not to mention clothes and paint finishes.
At the same time, battery manufacturers have designed maintenance-free batteries with different electrodes or plates, which results in less gasing and less fluid loss. So a maintenance-free battery is not simply an open-cell battery that has a cap over it, and it should not require as much maintenance.
Q: My question regards my 1983 Mercury Grand Marquis L.S., which is just shy of 100,000 miles. Until I reached about 85,000 miles, my gas mileage was about 16 m.p.g. in mostly city driving. Then, almost at once, it dropped to about 12 m.p.g. and then at about 90,000 miles went down to 9 m.p.g. This car runs beautifully, except for a minor loss of acceleration. I spent more than $800 for tuneups and testing to find the problem. I have been told it could be the timing chain or computer, but I don't want to spend the money to fix those items unless I am sure that they are causing the drop in mileage. Can you shed some light on the problem?--G.C.
A: The drop in fuel economy is drastic, so you have a definite problem. Since it occurred over a 10,000-mile period, it is something that degraded slowly, rather than catastrophically. Of course, any one of dozens of problems could be causing the drop in mileage.
Your Mercury has an electronic diagnostics system that operates through a central command computer. A qualified dealer should be able to determine if the computer has identified the problem already or if the computer itself is at fault.
Another possibility is that you have a dirty oxygen sensor. If the computer determines that the oxygen sensor has stopped functioning properly, it will automatically revert to what is called a default mode. In this mode, the computer sets the fuel injection system to an overly rich mixture that results in a drop in fuel economy.