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Cooling System Refill and Generator/Alternator Failure

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I replaced my 01 986 S Tip waterpump this week and completely flushed the cooling system. Following the factory manual instructions, during the initial stages of the refill, I pulled fuse B1 (key off) per section 19-14 to force open the coolant shutoff valve. This instruction was for Tip cars only.

Fuse B1 covers the instrument cluster and tiptronic, PSM, TC

The refill went well with no problems.

Afterwards, I discovered the alternator is not charging. I have not completed any serious testing, but I suspect the voltage regulator has been killed. I also suspect running the engine up to temp with the instrument cluster off is somehow responsible for killing the alternator.

Has anyone had a similar experiance? If what I suspect is true I wish I hadn't read the manual so carefully!

Signed, cool but powerless in Seattle.

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The generator repair shop tested it out of the car and said it worked ok.

On the car, the the voltage regulator 12v signal from the instrument cluster (key on) is present at the generator plug. The cable from the generator to the battery tests ok. I cannot find any broken fuses.

Back in the car, initially after startup it charges at > 13v. However, after a couple of minutes the charge drops back to zero and the battery starts to discharge.

No battery indicator light ever comes on, nor any other telltales.

My next step is to replace the voltage regualtor.


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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)

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Thanks for taking the time to share your repair procedure and the fruits of your research on the voltage regulator.

That item is one of parts that have been very difficult to trace down.

Let is know if you find out anything further on the difference, if any, between the part numbers and the long-term performance of the voltage regulator.

Regards, Maurice.

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  • 10 months later...
The voltage regulator was the culprit.

I may be the only guy who changes the voltage regulator as part of a coolant refill!


Thanks for the writeup! You're not the ONLY one changing VR after coolant flush. I just did my Tip and followed same instruction to pull that darn fuse. After a short few hours, my battery died. Until now I suspected that somehow the Alternator died coincidentally. I will definitely be replacing VR this weekend if I can get part from local VW / Audi dealer. Thanks again; you have quite possibly saved me hours of fruitless diagnostics. Only downside, no good excuses to down the Vodka.


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  • 1 month later...

To add a datapoint, I just did a waterpump on my '01S (58k) about a month ago. My VR died yesterday. There's certainly commonality here, perhaps not causality, but still...

Thanks all for your advice. I'm headed down to tackle the job in a few minutes.

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