Hydraulic vs. Mechanical Tensioner
 

How do I know if I have a merchanical or hydraulic belt tensioner on my X5?

I just replaced both tensioners and the idler pulley on mine.

Check out realoem.com, bavauto.com, ecstuning.com, your Bentley manual, etc., to learn the difference between the two types. Bavauto has a nice video of this replacement work.

Look in your drive belt area to see which you have. I might suggest using a flashlight at night and a mirror as needed.

I replaced my hydraulic accessory belt tensioner with a mechanical one. Purrs like a kitten!

Have fun.