Regulator or Alternator? ('87 Scirocco)

May be bad grounds... Check all ground wires, and clean/replace as necessary. Then re-test and see if there's a difference.

Had gone over the wiring previously (looks good and connections tight and clean). Also, I made sure alt belt was properly tightened.

If it cranks up to about 13v for some time while first driving, then I would think if it's a wiring problem, it should be in regards to the regulator feeding back into the battery. Because apparently at first the alternator runs properly. Over time it continues to drop down into the 'concerned' zone but that takes some time. So I'd think that would indicate a non-wiring issue.

-Phil K

I am sure you have already checked the heavy wiring between the alternator, starter and battery and the grounding of alternator and battery.

I would suspect the brushes first. Worn brushes won't let you run enough current through the field winding and thus will limit the alternator output. You are probably due for a new set of brushes anyway.

If new brushes does not fix it I would go on to replace the regulator.

Check the battery also. If you have a dead cell (or two) it will draw a lot of current. >

When I went over everything I yanked the regulator out and checked the brushes. They were fairly long - (about 1/2 inch or so) and well within spec. So I took a brush and cleaned all the carbon I could off of all the contact points for the regulator brushes.

I understand your point on the battery but think it's fine. May not make it through the winter, though, at this stage as the eventual low recharge voltage doesn't help it one bit.

Regulator is about $20-25 and a rebuilt alternator (nix, not Bosch) is about $60. The price doesn't get me, it's giving up the Bosch alternator. But I am at the point where it's almost no choice.

The symptoms of this are curious, to say the least. The Bentley doesn't really handle these symptoms.

Hi Phil,

If you checked all the wiring and all the connections are clean, you

*may* have a regulator problem. The regulator should increase the field voltage (or is it current) to keep the voltage at a fixed 13.8 Volts (VW's alternator always output 13.8V, anything else is not normal, based on my personal experience).

Maybe the problem get worse when the regulator warm up.

I once had a bad regulator that was allowing 17 Volts out of the alternator. My wipers were wiping like crazy!!!! And both headlights burned.

As far as alternators are concerned, I had good result with alternator rebuilt by Bosch, but I have seen off brand rebuilt that barely outputed

13V.

About the belt. Once, I had a properly tensionned belt that was slipping because it was worn. It wasn`t cracked but had gotten thinner and was going too far down in the pulleys.

Good luck.

Martin Quebec, Canada

Phil Boeye wrote:

My gut feeling is the regulator is bad. The transistor that passes the field current is probably getting weak and with rising temperature is unable to conduct properly. A new regulator by Bosch or Transpo should fix the problem. I prefer the Transpo because it has heavier-duty internals. Otherwise, it is possible for the rectifier diodes to be getting bad but checking them requires specialized test gear. I would recommend a trip to a good, old-time, independent automotive electrical shop to have it looked at if you want it rebuilt.

OK I'll make a couple of assumptions here. With a 90 Amp Alt, you have air conditioning. and you have the standard JH engine. I had the same problem with my 87 Cabby a few years back

First you might want to measure the brushes on the Voltage regulator. If they are less than 5 mm long, they have reached their limit.Replace the voltage regulator.

Second, when you tighten the alternator make sure the drive belt is good and tight. Unlike north American cars this is done using two wrenches on the adjusting bolt (not well described in the Bentley manual.

Hope this helps.

Thanks, guys.

I have a feeling it is also the regulator at this stage. Seems to me that the rise in engine temp does affect recharging, explaining why it operates properly at startup. Also interesting is that last night I drove it with just headlights (lowbeams) in about 30 degree weather. Doesn't seem to take that huge of a dip after warmup in cold weather, which would somewhat support the engine temp diagnosis.

Unfortunately, I can't locate a Transpo at this point. So I'll just pick up a local since I need it for the weekend.

-Phil K