The voltage regulator was the culprit.
I may be the only guy who changes the voltage regulator as part of a coolant refill!
It was a good learning experience. )-:
1) The water-pump was leaking but none of the coolant was dripping onto the floor in the garage. Instead, it was getting on the belt and burning off on the front of the engine. What little dropped down was collected by the under-tray and then burned off. the clue that made me look was a small drop in coolant level and a funny rotating noise from the pump bearing at low speeds.
2) Changing the water-pump was pretty easy. I didn't remove the seats and the hardest part was getting the under-tray off and on.
3) Mr. Clean and a tooth brush worked well to clean up the mess on the front of the engine, followed by warm water rinse, all administered by a hardware store spray bottle.
4) Draining and refilling the coolant went well. I used the drain plug in the bottom of the water manifold; it took a while because I didn't pull the vent hose but I wasn't in a rush. I measured the amount I drained out, 3 gallons, so I could make sure to put the same back in. I used Havoline Dex-cool extended life for the refill. With the vent valve open, and starting the process with the reservoir full to the top, on engine start-up the system immediately drank almost 1 gallon as fast as I could pour it in. Afterwards, closing the radiator cap and warming the engine at 2000 rpm until the thermostat opened, and then running until the radiator fans came on with short bursts to 5000rpm, it really didn't drink much more coolant. After shut down, I closed the vent valve, topped up the reservoir, and it was done. Sort of.
5) If I had to do it again I would not pull fuse B1 as suggested in the service manual. It didn't feel right then and now I'm sure. Without the 12v input from the Instrument Cluster telling the Voltage Regulator how to balance the output, the VR apparently died trying to do the job.
6) If you want to know how a charging system works some of the best sources are from the hot rod world. Google was great help for a guy whose electrical expertise ends when the smoke gets out.
7) The repair shop who tested my alternator out of the car didn't believe it was broken and proved it. The failure mode took a few minutes to manifest itself as the VR dropped the output to zero. Hopefully I can get my $20 back. Those guys cost me a week of head-scratching and heartburn. Here's to Martini's as a diagnostic tool.
8) Thanks to this site I was able to find a new Voltage Regulator. The original unit was an F-00M-145-225. There are no apparent cross references published to the Porsche alternator, but you can trace it to a lot of Audi's and VW's. The VW Beetle was the car I picked as my choice cross reference. Discountvdubparts.com listed the Beetle regulator under their part number W0133-1613555 for $67.95 (this is a common price on many sites) so I took a chance. The part arrived as an original Bosch p/n F-00M-145-350. I wasn't 100% sure if this could be used so I went back to Google and found a French repair shop that actually cross referenced the 2001 Boxster and both part numbers as being correct. So far it works…
9) Removing the Alternator was probably the easiest part of the job. The key seems to be backing the mounting bolts out about 3 turns and then tapping them on the head with a soft drift to knock back the bushings. Then, with a little patience and rotation, it falls right out.
10) Changing the Voltage Regulator is a simple bench-top job, remove the two big nuts on the back, and the two screws holding the back-cover on, and you can then access the three screws holding the VR down. Just take care with the brushes when you reinsert the new unit.
I think the root cause of all this evil goes to putting water in Porsche engines. If this car or my old 928 are any indication, Porsche water-pumps appear to be a regular service item.
$250 (water-pump) + $50 (coolant and gaskets) + $91 (VR w/shipping) + $20 (useless testing) = $410 (not including Vodka)