charging system problem - BMW Forum

joshydt58 · 01-16-2010, 08:27 PM

hey everybody im new to the forum and i have a wierd problem with my 2001 740i sport. after never having any problems with this car i started it one morning and my battery light was on. i wasnt at home so in the process of driving there i started losing electric components like the radio and the lights and so on. i figured it was the alternator and purchased a new liquid cooled alternator and replaced it. My battery light was still on so i replaced the battery and thought my problems were solved. no battery light on but then the car got warm and the battery light now go's on then off. if i shut off the car and let it cool down the alternator does fine until it warms up again. i unlocked the voltage on the dash and took it for a drive and the monitor shows around 13.5 volts until warm then the battery light comes on then the voltage goes down to around 11 volts and then it will go back off and the voltage will go back up to around 13.5 until the car is all the way warm then the battery light will stay on and wont charge the battery at all. if anyone has had this kind of problem and has any advice for me i would really appreciate any ideas or help. thank you.

marti5 · 01-17-2010, 05:21 AM

Sounds to me like a the alternator even though its new, is it from BMW or aftermarket??,also the alt should be pumping out around 14.5V

brettski · 01-17-2010, 06:37 AM

Can you hear the pitch of the altenator change at all during these different phases of the problem that might indicate a change in the load on the system is occuring? If you load the altenator up by turning every possible electrical device on whilst it is good, does anything happen?
(Marti) Just a line of thought, are there any engine management systems that change state during the warm up phase that might be screwy and load the electrical system up, eg Anti pollution system or cooling system?

marti5 · 01-17-2010, 06:47 AM

Quote:

Originally Posted by brettski

(Marti) Just a line of thought, are there any engine management systems that change state during the warm up phase that might be screwy and load the electrical system up, eg Anti pollution system or cooling system?

Only the pre heat cat cycle ...around 30 seconds,it does sound to me to be a duff alternator, if its an aftermarket one I would deffo say its a duff,Ive heard of people changing a/market ones three times over and in the end getting on from BMW, if its from the dealer..then its got an automatic BMW 12 month warranty with no quibble as they would pull the car in and test it for free.

I have started mine from cold -7, with everything on just for a test and it was still pushing 14.1V

joshydt58 · 01-17-2010, 03:16 PM

i cant hear anything but it is a beck arnley remanufactured from rock auto.com. is it possible coolant is not making it to the alternator to cool it. im also getting a dash code to check the coolant even though when i do it is full.

joshydt58 · 01-17-2010, 03:19 PM

yeah i have everything on radio, heated seats i roll the windows up and down use the power seats. its the same thing it just depends on the temp of the car.

brettski · 01-17-2010, 04:07 PM

Marti, is there a thermal sensor in the alternator?

joshydt58 · 01-17-2010, 04:24 PM

Quote:

Originally Posted by brettski

Marti, is there a thermal sensor in the alternator?

i wouldnt know. is that something thats common in alternators? i felt the hose thats running to the alternator and its warm so i assume that fluid is getting to it. would the thermal sensor be a internal component?

brettski · 01-17-2010, 04:33 PM

Quote:

Originally Posted by joshydt58

i wouldnt know. is that something thats common in alternators? i felt the hose thats running to the alternator and its warm so i assume that fluid is getting to it. would the thermal sensor be a internal component?

I am not sure if there is a sensor or not, if there is and its not functioning properly, maybe its tripping some sort of slef protection mechanism within the alternator or the car itself. I don't know. It might be worth contacting the supplier and telling them about the problem, see what they have to say, its there domain.

joshydt58 · 01-19-2010, 03:32 PM

well i bit the bullet and took it to a shop and marti was right the voltage regulator in the alternator was bad. thanks for the help guys i appreciate it.

brettski · 01-19-2010, 08:22 PM

Another goal for Marti5. He knows a lot of stuff