View Single Post
      10-19-2019, 03:40 PM   #22
aligoodn
Enlisted Member
38
Rep
34
Posts

Drives: 2011 X5M
Join Date: Feb 2018
Location: Augusta, GA

iTrader: (0)

I agree that is a catastrophically wiped bearing shell. The fact that the shell next to it (which I assume came from the adjoining rod) is relatively undamaged points to the clearance variation being too great between the two rod bearings and the loose bearing got all the oil. Path of least resistance.

There are plenty of internet opinions about BMW M engines an 10w60 oil, and the issue is especially confused by BMW switching S62's from 10w60 to 5w30 and then reversing their decision. My opinion, FWIW, is that there is no one correct oil for a specific engine that is universally applicable for all types of use and climates. Higher oil viscosity will create higher oil pressure at the expense of oil flow, and it is the actual flow of oil that cools the bearing surfaces so higher viscosity isn't necessarily better. The oil pressure itself is really just an easy way to verify the oil galleries are pressurized and that oil is reaching all of the parts of the engine that need it. I would encourage you to take oil pressure measurements on the engine before and after trying heavier oil just to see at what rpm the oil relief is lifting and at which point the oil pump can provide no more flow as engine rpms and bearing load rise. You can unscrew the pressure switch on the oil pan and use that as the point for measurement. As you mess with oil viscosity, you will find that thicker oil takes longer to reach steady state temperature and will result in higher oil temperatures than thinner oil.

The rod bearing issue I've seen on S62's (and I've probably done rod bearings on a dozen engines) point to the oil being too thick for the application. Those bearing shells typically look worn, i.e. copper showing, but are not wrecked like your picture. Also of note, all of the bearing shells exhibit similar wear in those engines, which rule out a clearance from a manufacturing standpoint. The overall clearance is too tight, but the variation from rod to rod is not high enough to cause drastic wear differences between adjacent rod ends.

I usually start with manufacturer recommendations for oil weight and then adjust. My usual strategy is to reduce the oil viscosity until hot oil pressure at idle is at the minimum acceptable pressure published in the engine specifications. Most engines will be somewhere in the 10psi range at idle. For my S62, 5W50 seems to make the engine happy. For the S63 engine, 5w30 has been pretty good and I'd be hesitant to go thicker. Thicker oil can be used as a bandaid for bearing clearance, but at the cost of total oil flow to the engine.

Of curiosity did you ever pull an oil sample on the engine with the failed bearing or notice any material in the oil filter?
Appreciate 1
TTV8M113.50