Need to get car going.

[Thtbrokee30sht]

I have a 1996 bmw 328is, well when I bought it it was perfect for about 7 months then things started going bad. I replaced the battery, radiator, alternator and serpentine belt. I installed the alternator the other day, and installed the main drive belt. Well the belt isn’t as tight as it needs to be and idk how to adjust that. I followed the correct diagram for the routing so idk what’s the deal. When I start the car I have to use jumper cables, once the cars running I take the cables off and the car dies within 30 seconds, so I’m thinking since the belt doesn’t have enough tension on it then it’s not spinning the alternator fast enough to charge the battery/ and or keep the car running. This is my first bmw so anyone please help. I miss driving this car so much.


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[Eric93se]

Take that belt off and bring it back to the store. Then compare another brand with that belt. Another possibility is that the tensioner is bad, you probably have the spring tensioner (there is an upgrade to hydraulic/spring) but the regular spring style works fine, but your could be lame.

Here is a link to a new one:

https://www.ebay.com/itm/INA-Belt-Tensioner-Assembly-BMW-E34-E36-Z3-E39-E46-E53-E60-E83-E85-OEM/121213623114

[Eric93se]

Also just to note, if the belt is in fact slipping or loose then you could be slipping on your water pump and that is something you don't want. It could overheat and that costs big bucks even if you know how to fix it. I would recommend not to drive it till you know its fixed.

[gdavid]

Do you have a battery charger to bring your new battery back up to charge? Even without the alternator putting out power, the engine should run for a good while (15-30 minutes) depending on battery health and load with a bad alternator. If you don't have a battery charger, just leave it jumper wired to the other car and let that alternator bring it up some. Regardless of the alternator performance, you need to get the belt turning your water pump or you will have serious problems.

Did you compare the length of the new and old belts? Your belt is likely sized for the 325 which used an idler pulley that the 328 did not for some reason. The simplest thing to do would get another belt and make sure it is smaller than your current one. Take a picture or describe what style tensioner you have, the earlier ones (and most) had a spring style that you rotate and put a pin though to hold back while changing the belt, do you have this style or the piston style which looks the same as the AC compressor belt tensioner?

The first picture below is the 325 (m50b25) belt routing and the second is the 328 (m52b28). Note the additional idler pulley near the oil filter. I don't know why they quit using that pulley.

[alang1990]

I suppose they quite the idler pulley because they used a shorter belt.

Dude you've got a belt that is too long. Its a simple thing to fix. You can check realoem.com plug in your vin and see exactly which belt you're supposed to be using.

[gdavid]

I suppose they quite the idler pulley because they used a shorter belt.

Dude you've got a belt that is too long. Its a simple thing to fix. You can check realoem.com plug in your vin and see exactly which belt you're supposed to be using.

I like the idea of the idler pulley because it increases the belt contact area over the alternator pulley but they must have done away with it for some reason. It includes a bracket that the top alternator bolt passes through to hold it, you need a longer bolt to use it and I could see the pulley getting out of alignment pretty easily. I guess it was more trouble than it's worth. I don't know if it can(should) be used in conjunction with the new style tensioner(which I don't have).

[Thtbrokee30sht]

UPDATE: I said screw it and took the alternator to autozone and had it tested. The results came back faulty multiple times. So they ordered me a new alternator after work today I am going to installl the new one, and I was unable to compare the old belt with the new belt because the old belt broke off and idk where it went. My tensioner has a 16mm nut that I have to “tighten” (push tensioner down)
with a socket and it looses the tension so you can take the belt on and off.


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[Thtbrokee30sht]

https://uploads.tapatalk-cdn.com/20181029/0617345bcaf762432123f3143e62faa9.jpgthat’s the tensioner to the left


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[alang1990]

Belt is clearly slack very slack.

And you shouldn't be able to tighten the tensioner. It is an auto tensioner with a spring. The nut gets you the grip that enables you to leverage and compress its internal spring, loosening the belt and allowing you to remove and replace the belt. Then when you release it auto tensions. This system maintains belt tension by automatically adjusting to the belt as it lengthens slightly over time while in use. That is not possible with the old tensions by hand and secure bolt to the rack method.

[woody328is]

Regardless what the auto parts store told you the belt looks too long. I'd replace it before believing a $10 an hour autozone expert.