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Old 08-11-2000, 10:19 AM
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hi, would like to find out what are the "correct" voltage readings for a W123 when the engine is off, and when the engine is idling/revving.

am wondering if the voltage regulator on the alternator is okay. thanks.
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Old 08-11-2000, 11:53 AM
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If your goal is to determine if the alternator is charging the battery, the exact readings are not critical. With the engine off, it will show something like 12.X or less. With the engine running, you should read about 13.4 on up to a little over 14, depending upon the state of the battery at the time. If you're reading mid 13 or better with engine running, the charging system is probably okay.

Good luck,

Larry Bible
'84 Euro 240D, 523K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles
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Old 08-12-2000, 12:33 AM
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thanks larry. i just changed a new batt, and the "engine off" reading is fine at abt 12.4.

BUT with the engine at idle, the voltage drops to about 12.1! And on revving, it goes up to about 13.1.

can i conclude that the alternator is on its way out? has it anything to do with the voltage regulator?
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