[fatty335]

I have been studying failed rod bearings in the early n55s for quite some time now. After reading as much as I can on the subject, and based in no small measure on BMW's oil priming TSB, I'm more inclined to believe bearing failure is being caused by oil starvation due to air introduced into the oil circuit that the variable displacement oil pump cannot clear than by any other event or circumstance (contamination during OFHG repair, extended oil drain intervals, insufficient bearing clearance, cumulative damage, etc.) short of high-G cornering during racing.

As such, I noticed BMW eliminated the wheel well-mounted external cooler and lines in many of the later model n55s:



and went with an oil-to-coolant heat exchanger instead:



Theoretically, eliminating the external oil cooler and lines would greatly reduce the chance of air being trapped and circulated through the oiling system during a repair and causing a spun rod bearing. I’m hypothesizing this was at least part of the reason BMW switched to this setup. Would be interested to hear from any techs or engineers…

[flapeo]

What about n55s that didnt have the external oil cooler? did they still experience spun bearings after OFHG?

[neilvan]

The air to oil cooler is much more efficient and an upgrade to the coolant to oil.

The Air bubble contamination is during the feed which is after where the oil cooler will feed/return. Also due to the nature of it closing and opening it is put in a place where air cannot be and it won't be starving the engine.

The N55s(later ones like the X3/X5 etc) had the coolant/oil version and as stated some had no cooler; All of these engines also experience oil starvation after OFHG changes

[anjuna]

ayyyyy lmk if it's a bolt on and I'll try it out.

[lforter]

yeah, I have been noticing people wrecking their engines more often. Mine is a suspect as well but I havent taken the oil pan out and checked. Will do it at the end of the month and report it. Personally, I believe the problem is not the bearing itself, but rather something in the oil system as you said. it is hard to say what part specifically without any logs or deep study.

I don't think its the oil pan, I mean for track problems sure. But for people on regular use getting spun bearings because of an inadequate track oil pan sounds odd. Something around the oil pump system is not adequate.

[neilvan]

Originally Posted by lforter

Personally, I believe the problem is not the bearing itself, but rather something in the oil system as you said. it is hard to say what part specifically without any logs or deep study.

I think this is pretty accurate. The rod bearings are the same part # for N54/N55/S55 and the main bearings are the same for N52/N54/N55.

As well the oil pump is the same part for N54/N55.

And the oil filter housings (all versions from non oil cooler to air/oil and water/oil) are all the same for the N52/N54/N55.

So why is the N55 so much different than the rest? Is it just the casting past that much different and more susceptible to that initial air bubble when swapping the ofhg? why knows

[anjuna]

I'm not sure why people don't
-drain coolant
-drain oil
-run water pump to get rid of the rest of the coolant
-pull the oil filter
-let everything drain out
-pressure wash the SHIT out of the area surrounding the OFH
-swap over new OFHG or OFH
-refill all fluids
-hand crank (literally, hand on ratchet on crank a few times over)
-crank with plugs pulled
-reinstall anything else i left off
-go about their merry way

[fastboatster]

Originally Posted by neilvan

I think this is pretty accurate. The rod bearings are the same part # for N54/N55/S55 and the main bearings are the same for N52/N54/N55.

As well the oil pump is the same part for N54/N55.

And the oil filter housings (all versions from non oil cooler to air/oil and water/oil) are all the same for the N52/N54/N55.

So why is the N55 so much different than the rest? Is it just the casting past that much different and more susceptible to that initial air bubble when swapping the ofhg? why knows

oil pump p/ns are definitely different for the n54 (11417560250) and n55 (11417573747), even for the e chassis cars.