Quote:
Originally Posted by Happy Jose
The bolts are aluminum. In fact, BMW uses aluminum bolts in all sorts of unexpected places like the pans on the transmission and engine. These are one-time use, and the new ones have to be carefully torqued into place!  |
https://bimmercat.com/bmw/EN/search/selectCar/E82/Cou/BMW+135i+N55/ECE/11_4465
Oil filter housing bolts are steel. Even on the first generation N52 they are steel.
N55 sump does have aluminium bolts
Only sure way is the magnet test which is also advisable before removing a fastener so you know how much strife you'll be in when it flies into the abyss