996 voltmeter reading

[griffter]

I've googled this and understand dodgy cabling, earth points and heat-soak affected regulators can play a part, but my question is, is anything really wrong or does my voltmeter just under-read? Anyone had similar symptoms and done anything - or not?

So my 996 has a new big powerful battery, and the voltmeter reads under 12v with the ignition on. When I start the engine the reading goes up to over 14, but over the next minutes/miles drops to just over 12v. This is pretty much where it stays, with a little gradual fluctuation. Hitting traffic and sitting idling, the reading will drop below 12 and sometimes as low as 11 with lights/ac on, but always a bit above the ignition on / engine off reading.

I've done 500 miles at least half with the lights on and the car starts with a healthy turnover each time.

Is the voltmeter reading the battery voltage or the alternator output?
Is there some sort of intelligent regulation of battery charge?
Am I just seeing the effects of car lengths of cabling between the battery and alternator heating and cooling and carrying different currents depending the state of charge and the electrical demand?

Any opinions or experience welcome. The bottom line is that I'm not really concerned because the system seems to be working OK - if it wasn't for the voltmeter I wouldn't have noticed anything. There have never been any warning lights.

Thanks.

[griffter]

Thanks all. It sounds like it'll be difficult to convince the warranty company anything's wrong without actually breaking down. The dealer's said tadts.

But if I can diy for £40 I may as well save the argument and a "warranty approved" garage breaking bits on my car.

Interestingly with a multimeter, battery and engine bay +ve read 11.6v - more or less exactly what the voltmeter does. But I guess if that's all the alternator's putting out, that's all the battery will produce. I've tried a trickle charger too but I need to give that a bit longer to see if it'll increase the voltage on the battery.

[griffter]

Thanks all for your helpful guidance.

Update: I bought a bosch regulator, part no. ending 350 (top) instead of 255 (bottom) from eBay. According to pelican parts thread (see also below) and other sources these are equivalents. In fact the 350 is listed for a 1.9 tdi 110 Skoda!:



I fitted as per pelican parts thread:

http://forums.pelicanparts.com/porsche-996-997-991...

It's straight forward enough, but you need a variety of tools Eg to lever the alternator out, and I took my time cleaning and checking things like the air flow meter, connections and wiring along the way. I also cleaned and silicone greased all the alternator / starter / 12v post connections.

The only new tip I can add is that hitting the bush in the alternator is never going to budge it. You've got to lever and jiggle the alternator out. But then on the bench you can use a threaded bar or bolt, washers and sockets to press it back (in my case with lots of plusgas and copper grease as well):



Then in my best Haynes manual voice,

"refitting is the reversal of removal".

Job done. 14v all the way.