[Vwdiesel] HELP-Battery voltage when glow plugs kicking in.

Lee Hillsgrove hillsgrove at adelphia.net
Mon Oct 6 21:23:37 EDT 2003

> Tested my battery voltage today (about 12' C outside at the time)
> 12.65VDC (no load, car been parked 6 hours)
> Ran glow plugs (just 1 cycle) and voltage went down to 11.6VDC while under
> load.
> After the single cycle, battery voltage was sitting back up @ exactly
> Started car (of course, one more cycle automatically) and voltage slowly
> crept up to 12.04, 12.05. etc. to 12.1VDC after around 30-40 seconds.
> I had to stop "test" & run back into work, LOL)
> Does that voltage seem a bit low to you all?

  Yes, it does. Should be about 14 volts while it's running. Sounds as if
the alternator is not charging. I would not automatically blame the battery,
but look at the charging system first.
 If you did not blip the throttle after starting it, this is normal
behavior! You will need to bring the rpms up to as much as ~2500 before the
charging circuit will come alive. You can usually see the lights brighten up
when it begins charging.

 Try it again and make sure the alternator is doing it's thing. If it does
not after revving the engine, you may need brushes, the second most common
cause of no charge.


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