[Wanwansuii]

Hello all,

So for the past few days, I have been lurking on the F10 5 series forum to see what issues I may come across with the N55 motor since there are way more 535s than 640s. As we all know, the N55 is known for issues surrounding and/or increased maintenance of valve cover gaskets, spark plugs/coil packs, water pumps (a long-standing BMW problem), and the notorious OFHG.

In my research, I'm finding several motor seizes that eerily occur several miles after the replacement of the OFHG, which does put some fear in me. Supposedly, from what I'm reading, it seems like the cause is an air bubble that develops in the oil cooler during the OFHG replacement, and supposedly the oil pump should be primed three or so times before restarting the engine after the procedure to properly lubricate the internals.

This is a bit concerning since I drove my N52-powered E92 coupe up to 200,000 miles with minimal to no issues and not a check engine light in sight; and the engine sounded and performed just like new. OFHG went at 175,000 miles and only took 40 mins to replace, and drove completely fine afterwards.

While I know that the N55 is generally considered much more reliable than the N54, what are all of your thoughts/experience/knowledge on this? Is this something 640i owners should be concerned about? Have you had any issues surrounding this?

I'm thinking of using Liqui-Moly 5w-30 oil going forward.

I will post a few links that allude to all of this!