Bosch vs Valeo Alternator

[Jamminman]

I have an '87 911. Mostly just drive it for short <20 mile drives. I usually use an optimate tender but found if I don't put the tender on, the battery is dead in 2 weeks. It will jump and charge just fine with the optimate. I drove it on a longer drive (started fine) after it sat for a week and a half and after it was parked for a half hour it wouldn't start.

The alternator light doesn't come on...ever.

Battery voltage with ignition on is 12.62
Battery voltage at 2000rpm is 12.41

Thinking the alternator is toast but can't really explain why the battery goes dead after 2 weeks unless there's a small draw on it somewhere.

Rock Auto has new alternators (I've seen some threads that note remanufactured ones are suspect). They have a new Valeo 432794 for $331 and a new Bosch AL401N for $427. Any pros of one over the other?

[walt]

Those voltage readings are low. Try and clean off your two ground connections before you go the alternator route.

I went with a Valeo alternator after reading some negative comments on Bosch.

[timmy2]

Have you checked the lamp in the gauge that never turns on is good?
If burned out, the alternator won’t charge the battery…

[Jamminman]

Seriously? If the bulb is burned out in the idiot light the alternator won't charge the battery? I am pretty sure the bulb is out.

Is this the correct replacement?


https://www.autozone.com/electrical-and-lighting/side-marker-light-mini-bulb/p/sylvania-longlife-mini-bulb-3893ll/493803_0_0

[timmy2]

Seriously, in simple terms it uses the load to calculate the charge needed.
And yes that is the 4W lamp you need.

[fanaudical]

Yep - Just another charming feature of the 911 electrical system...

[Reiver]

Do you have a newer radio/CD system that maintains input? That is a constant electrical draw and will drain a battery if sitting for extended periods.
I keep my 83sc on a battery maintainer when not is use but my plug in amp gauge (cigar lighter) indicates 14.1...13.9 when I start up and maintains in the high 13's when driving.

[Hotshot]

Valeo is now OEM for Porsche classic. I like new vs Bosh rebuilt. Check those grounds first. went through this..

[wazzz]

Or you can keep the original Paris-Rhone alternator and have it rebuilt or rebuild it yourself. But first check the bulb as said before. Maybe replacing it is all you need to do.

[darrin]

Where are you located? I second the recommendation of having the alternator rebuilt locally (if there's a good shop/person in your area). As discussed in other posts, even many of the "new" alternators available seem to end up being rebuilt these days (with questionable quality). I'd also recommend having your battery "load tested" at a local FLAPS, especially if it's getting old(er). Finally, do your interior dome lights turn on/off when you open doors (especially the driver's door). A failed dome light switch (pretty common with our cars) will leave a relay that provides power to the power window circuit energized/activated and the drain caused by that active relay will provide just enough load to cause a healthy battery to drain in a few weeks (you can also check this by trying to operate your power windows with the key out and a door open).

[mepstein]

I get my alternators and starters rebuilt at a local auto battery shop. $75-125 depending on parts needed and turns around in a day or 2. Much easier than hoping the one you order works for your car.

[Jamminman]

I'm in the Twin Cities, there's a Porsche shop nearby I can call to see who they recommend for a rebuild. I'll do the alternator light this week and report back...

[47silver]

I second the get it rebuilt. You know it will fit.

[Tea Tray]

I second Darrin above.
The power window relay/door switch caused my ‘87 to discharge the battery.
A good way to test for a draw is to disconnect either battery terminal and put a test light across the post and terminal.
If the light glows, you have a draw.

[Jamminman]

Well the plot thickens a bit (just got a new pup so time's at a bit of a premium). Put a new bulb in but still doesn't come on with the ignition in on position. If I ground the bulb against the metal casing inside the tube of the gauge the bulb slides into, it comes on. Tells me bulb is working at least.

Yes, my dome lights don't come on..... initially. Here's where it gets weird. Neither passenger or driver door switches worked and for a brief moment, both power windows would go down and up with ignition off. Then that stopped. I removed the rubber boot on the drivers side door switch and now it's working. Passenger still doesn't work.

[Jamminman]

[Jamminman]

Replaced alternator and the alternator light is working now. Also, the battery voltage is now 14.5 with the engine on.

[Tremelune]

Regardless of the condition of the alternator, putting the car on a tender if you won't be driving it for a few days will get you more years out of your battery. They're $25.

[mysocal911]

Originally Posted by Tremelune

Regardless of the condition of the alternator, putting the car on a tender if you won't be driving it for a few days will get you more years out of your battery. They're $25.

Really? Are you guessing or can you please explain in detail, and not just provide your anecdotal view? You are an engineer, right?

[John W.]

As a EE, I don’t see how a tender will increase battery life. If a battery gets fully discharged that will degrade it some and shorten its life so a tender will prevent this.