Battery or Alternator Problems
 

I have a 1993 300SE. I believe that the battery is going bad but it has never shown signs of not holding a charge. Before I take it out can someone tell me the easiest way to check to see if the alternator is working properly? Can I just check the voltage output at the battery while the car is running? I know on my Suburban the output is 14.2 volts but when I tried this on the Mercedes I got a much higher output. The car has never had a problem until I recently had someone else change the oil (I have always changed it myself but got lazy), they put in a new, but not quite correct, drain plug and it leaked oil all under the car. Oil now seems to be all over (an exaggeration as the engine is actually quite clean except for the underside now). Suddenly I have this problem. Any thoughts? Thanks for your advice.

good alternator-voltage charge while car is running should be 13.5-15v on most cars...

I have never heard of the alternator putting out too much voltage. Usually the brushes in the regulators wear out and the voltage drops. You could have a bad regulator in which the internal circuits have gone bad but the brushes are still good. I notice on my Chevy that if the battery is weak it will put out about 16 volts until the battery is charged. Then it will drop back to 14.

Tell you what, put the battery on a charger overnight then check the alternator voltage again. It could be just the battery going south on you.
If the voltage is still too high, I would replace the regulator and then check the voltage again.

Good luck!

You didn't really say what the problem is. What is it doing or not doing? How old is the battery?

Mike

On my 87 260E, I had a situation in which the battery voltage was higher than 15V at idle and the voltage would increase further when the rpms increased. It was not the voltrage regulator as I also thought at that time but the winding that was having a problem, dont quite know the exact specifics now, had to get the alternator rebuild to fix the problem.