I also had the dreaded alternator light go on in my e46 m at the same time as this post , my car one was replaced under plan at 80 thousand kays , and the one that I took of turned out to be a valeo remanufactured in Poland[so says the label , BMW was skelm here] .So after speaking to all the GUrus , some who own these car , who swore high and low that only an M3 alternator is compatible , I had two option , used original which would have been Valeo , new from agents [big money] also valeo ,or Diesel electric price around r3500 but also valeo , mine could not be fixed because armature burnt. So I sat at a friend place who happened to have a E46 323 I that was in for a service , I happen to have my alternator with me , compared the two and saw they look the same from the top and the 323 's was also 120 amp and it was a bosch.I went to a scrapyard where I knew a car like that was be parted out , took off the alternator myself , Saturday discount r850 , thank you very much , had the Bosch part checked , all well .fitted the Sunday ,hit a snag , does not fit freely , then realised the M3 alternator has no cooling duct as part of plastic backing cover , trimmed the cooling duct and the place where the hard oil lines go [easy because it is plastic] , bobs your uncle , fits perfect ,also noticed that the pulley size is bigger on the M3 alternator [revs higher ] , swopped the pulley of the Valeo onto the bosch alternator[use a impact compressor tool to loosen the retaining nut ] , so you don't damage the pulley , if you do they are available at AUTOMAGNETO in Cape Town for around r600.
I put everything together with new tensioners [belt looked alright] and it has been working fine ever since , with the money I saved here I spoiled the car and bought a genuine battery from BMW because the one in my e36 m lasted for seven years.
I don't know how BMW fitted the steering reservoir right up against the alternator whilst on the other E46 models the reservoir sits on the side of the cylinder head and is easy accessible , maybe that is why the alternators fail on the M3 , because the powersteering fluid heating up right against the alternator and there is no cooling duct on the M3 alternator because there is no space ,I want to relocate the reservoir one day when time permits . Now I have a diy friendly bosch alternator on the car with parts more freely available and cheaper to boot.
So one can get away with saving money on an Old M .
