Alternator problem. When the engine is cold voltage output 12.9-13.1V
 

Hi everyone,

i need some advice regarding the alternator. (car mercedes r320 cdi)
When the engine is cold the alternator is giving somewhere 12.9-13.1 volts. When idling or when revving it. It does not change much. When turning on majority of the consumables, voltage drops to 12.6-12.7.
When the engine gets warm, voltage goes up, up to 13.4-13.5.

As far as i know, this alternator has to give up to 14.2-14.4V output, depending on load, would drop to 13.8V. But what it gives now i think there is a problem.

The battery is half year old. Good quality, powerful battery, to the specs for the car.
I was guessing the cable connections. Cleaned them all (battery, starter, alternator earth and + cables), they did not look bad. No change.
Then i thought possibly the regulator is faulty? dont know hot to check it, so replaced it, it did not do any good. No change again.

Do not know what to target next?
Alternator itself? windings on the stator? rotor?
clutch pulley? maybe that one does not lock? (will check this next)
belt is one year old, tensioner as well.

Did anyone faced anything similar? what was the cause of it?

Any comments welcome.

Thank you in advance.

Start with voltage regulator. Possible failure mode is a diode is heat-sensitive.

Hi

thank you for the reply.
but i did replace the regulator. There was no change. Or possibly the regulator i bought was faulty? Bought it from mercedes, original part. Would be hard to believe its faulty. Are there any other parts sensitive to temperature changes?

thanks!

Never replace just the regulator. Just replace the whole assembly. Will save you headaches. I use bosch remanufactured alternators and starters with no issues.