Quote:
Originally Posted by R_don_abon
There's no way lubricating the threads affects tightening torque.
|
A given tightening torque for a dry thread and oiled thread will produce a different strain and consequent clamping force in a bolt. In the context of an oil drain plug bolt, I’d expect the tightening torque would be specified for an oiled thread.
Engine oil increases bolt strain by about 1/3 compared with a dry thread. An M12 8.8 drain plug bolt into aluminium at 20mm thread depth can take a torque of about 60Nm dry or about 45Nm oiled, so a BMW standard torque for an oil drain plug of 25Nm is well within the safety tolerance.