Pelican Parts Forums - Which alternator- rebuilt vs. new?

First, I would question the advice to replace the alternator unless something is wrong with it, like a blown diode, but this absolutely shows up in a test by a competent shop. If the slip rings are OK and the bearings good, I would just replace the VR. Or have the alternator that's in the car rebuilt, takes a couple days. Don't let them exchange it.

That said, I would rather put a rebuilt Bosch in than a new Valeo. The Bosch design has proven the test of time as a reliable alternator, whereas the Valeo is French. The French can make a cream sauce that will make a grown man weep in culinary ecstasy, but when it comes to alternators they aren't as good as Bosch.

Not that Bosch is all that terrific, but what can you say about an engine design that places the alternator three inches from an engine with 350 degree cylinder head temperatures and vibrations? Maybe replacing the alternator isn't such a bad idea.

My own experience with a Carrera Valeo is that it was very stable in voltage, but the one time I got it too hot, at the PCA Club Race at Gingerman over in West Michigan, the freaking voltage regulator decided to throw up its hands due to overheating in practice. Of course, in a pre 1990 911 you can't tell whether the alternator warning lamp is on because the VR has given up or the fan belt broke, causing you to come in. If this happens in a race that cost you $3,000 to enter and transport to. . . well . . . the best option is the old school Bosch with the voltage regulator mounted outside the engine compartment away from heat and vibration, like it is in small airplanes.