Unofficialbmw.com

[cmcon98]

This winter. I've noticed that when my E30 is idling with the lights and heater fan on, the lights are a little dim and the fan a little slow. When I raise the rpms from idle speed (around 750 rpm) to arount 1000 rpm, the lights brighten and the fan speeds up to normal speed. If I let the car idle with a lot of draw on the charging system (lights, heater, rear defog, etc.) the battery will be weak the next time I start the car. The battery is relatively new, and the alternator is of unknown age.

Does anyone else have this symptom? Is the stock 90 amp laternator sufficient for the car? I know the early E34 525i with the M20 motor used a 140-amp alternator. Is this a good swap?

My car has lots of stuff that draws on the charging system in the winter, like a fan-driven rear window defogger (it's a cabrio) and heated seats, so I wonder if a more powerful alternator would help.
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Cirrusblau '88 325iC 5-speed
Cosmosschwartz '99 M3 'vert 5-speed

[85-325e]

your voltage regulator may be going. I'd check it anyway. It's a checp fix if that's it. The brushes wear down and one day, your alternator doesn't charge. I think the part is like $30.
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Cosmo - 1985 BMW 325e, Single Owner, 265,000+ ORIGINAL miles and still going strong! But now on the East Coast and the salt air corrosion is eating my beautiful car alive...

[beejay]

possible VR, but usually if charge rate is OK unloaded and drops off with more load it's more likely the alt. but the VR should be replaced as well since they are cheap. Is your ALT the original?
Mine has been replaced with a rebuilt by the PO and does the same thing although not as bad as yours. Lights dim a little at idle. I've been thinking the same thing that a higher output alt might be needed.
It seems to be working OK so it's lower on the list of things to look at.

I'll have to do some poking around to see whats out there.
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Bob
92 325ic gone
14 BRZ ltd
05 Tundra SR5 TRD
01 VFR800fi - 03 DR650S - 83 CB1100F - 82 CB900F - 69 CB750

[cmcon98]

The alt looks original, so I'll probably replace it. I wonder if I'll melt anything if I replace it with an E34/M20 140 amp alternator??
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Cirrusblau '88 325iC 5-speed
Cosmosschwartz '99 M3 'vert 5-speed

[beejay]

[cmcon98]

It looks like a bolt-in, althougn the 140-amp has an air intake shroud with a flex hose connection like the E36 alternators have, so you'd have to connect a hose and run it to a scoop behind the grille. Bet the E36 hose and scoop would work.
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Cirrusblau '88 325iC 5-speed
Cosmosschwartz '99 M3 'vert 5-speed

[tncean]

I second 85-325e on the VR. Takes less than 1 hr to replace. Suggest discon battery... one slip of the screwdriver and can get right sparky.

tncean

[cmcon98]

Yea, I suppose I agree on the VR. I pulled it last year and the brushes looked good, so I reinstalled it. It couldn't hurt to replace it. I think I should be able to leave the car idling with every possible factory electrical accessory turned on and not discharge the battery. I know the idle speed is about right (750-775) so that's not it. So I'll try replacing the VR. Thanks for the advice, folks.
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Cirrusblau '88 325iC 5-speed
Cosmosschwartz '99 M3 'vert 5-speed

[tncean]

A bit of an afterthought... couple of years back I tried replacing just the VR, but the alty was just done. Ended up getting a "lifetime" warrantied alty from, I think, Advance Auto for maybe 100$ (or less)... I keep the VR in my "extra" bag, along with a CPS, and a relay, a light bulb, or 2.

Will suggest making a photocopy of a receipt, as the thermo-paper printout from the store will soon fade.

I've also switched to "Green Stripe" alty and ac belts... less squeeel, fit better than Conti.... to me.

Good Luck!

tncean