Is my alternator bad?
 

I have had the alternator checked twice on my 85 Euro 190E 2.3 16V - they say it's ok. I have tested the voltage at the battery when the car is at idle - 12.5 volts. When I drive the car, the voltage stays at 12.5 for a while, then intermittently drops to 10V, then returns to 12.5V. (I recently bought a LCD voltage meter that plugs into the cig lighter so that I could see the erratic voltage when I drive the car.)
Is my alternator bad or do I need a voltage regualtor (I suspect a bad regulator would show over 14.5V being produced. Could it be a loose connection? Any advice would be greatly appreciated.

M. Rossi
pirltd@yahoo.com

You would know its bad when the battery don't charge and the noise runs you up your wits.

The brushes inside the alternator could be wearing down. It is a fairly simple job to replace them and much cheaper than a new alternator. I had mine done this time last year when I had similar problems to yours. No problems since.

My 300E had the same problem. The alternator bench tested as being good, but the battery was not charging. When I replaced the alternator my problems were solved. It is probably an intermittent problem caused by worn brushes as 420SEL indicated. Since my wife drives the car and hauls the kids around in it, I went with a new alternator versus fixing the old one.

Well, thanks for all of the advice from you guys. The problem turned out to be corroded contacts on the alternator. I have had this recurring problem with other contacts on my car. Runs like a champ now.

mrossi

Well done!
:)

How much did the parts cost you?

Parts cost me nothing. I unplugged the alternator and sanded the contacts. I have had to do this to alot of the relays in my car also.

mrossipir