It's cold outside and my car wont start unless I use Jump Starter - 2004 325i

[nuby]

Hey guys, I've owned my car since June of 2015 and have noticed a common theme around Winter.

Winter of 2015 wasn't very cold at all so I didn't run into many issues but did have to use the jump starter when it was cold outside, since the weather warmed up fairly quick the issue went away rather quick and I thought nothing of it since the car had nothing else going on with it.
Winter of 2016 for 2 or 3 weeks, daily I relied on my jump starter to start the car as it would simply not start. I took the car to the mechanic to check my battery since my jumper showed it had LOW charge, but they said it was fine on charge when they tested it. The issue persisted until I gave in an purchased a new higher rated battery and the issue went away.
Winter of 2017... this issue is back again, I cannot continue to rely on a jump starter or buying a new battery every year...

What should I be looking for? This ONLY happens in the winter, all year round I have not a single issue at all.
If I jump the car and drive 3 minutes, walk away for 5 minutes and come back, it will be dead. If I jump the car and drive for 30 minutes, same thing...

[dworthy]

Sounds like a weak alternator to me, for that will keep killing a battery out. So you can use a multi-meter while the car is running or do this: https://www.youtube.com/watch?v=ra7yx_y_zV0

So you should be getting anywhere from 13.5V with a full load on the car to 14.1V with no real load on the car.

[MarcoZandrini]

To add to what Darin has written, BMW sourced alternators from Bosch and Valeo of France. The only way to tell which alternator is in the car is to remove air cleaner box and the upper intake hose. You’ll need a flashlight and a small mirror to read the label on the back of the alternator. Hopefully your’s is a Bosch. Btw, the two brands are not interchangeable without major efforts. The voltage regulator is replaceable but the alternator has to come out. A Bosch voltages regulatis should be less then $50 from a major online vendor. Try fcpeuro.

[nuby]

I was able to locate and identify it's a BOSCH alternator.
I tested the voltage as the video instructed, on idle it runs at 14.0V, on load it hovers around 13.7-13.9V

[dworthy]

That should be just fine, for at full load, you don't want it to drop below 13.5v

So what I would do next is go back to the battery. You need to clean the positive and negative post connection and ensure they are tight. Tight like you cannot move them with your hands. Next I would go to the passenger side of the car and clean the ground cable, both ends. The cable will be located near the motor mount and will be a large brown wire.

[nuby]

In the trunk, all connection are very tight and in very clean condition. In the hood, I only see the red+ wire, this is basically what I see. Nothing connected to the OEM ground terminal.angeleyesv222.jpg

[dhinez]

In the trunk, all connection are very tight and in very clean condition. In the hood, I only see the red+ wire, this is basically what I see. Nothing connected to the OEM ground terminal.angeleyesv222.jpg

You may need to jack the car up in the front passenger side. The ground cable he is talking about connects to the engine mount bracket to the frame of the car.


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[nuby]

I see it, looks like it'll require some disassembly, I'll need to go to my parents place to use their tools