[m6pwr]

I'm coming in to this thread a bit late, but I do have an interest (I've got an N54 in an '09 Z4). And I have a couple of thoughts that might be of interest re oil and the N54.

The problems associated with direct injection engines (not just the N54 but apparently all di engines) are fairly well known by now. There have been SAE papers on the subject and research is underway by at least one piston ring manufacturer to try to address these problems. And on the BITOG (Bob Is The Oil Guy) forum, a lubricants engineer who regularly attends the 24 Hrs of the Nurburgring race, and meets with race and lubricants engineers there, recently posted rather cryptically that the topic of the hour at the last race was the problems associated with direct injection (which is becoming pretty much the standard in engine design). When I sent him a pm to ask for more information all he would say is that the problems would have to be solved by the engine mfrs, not the lube mfrs. Nice.

The problem is fuel dilution. DI engines operate on much, much higher injection pressures than the "old" port injection engines. In the N54, fuel is injected at 1200-1700 psi, compared to about 45-75 psi in a port injected engine! Pretty amazing. That means higher blow by of fuel past the rings and more "wash down" of the oil film on cylinder walls. The fuel dilution in turn causes two major problems with the oil: viscosity loss (shear back) and significant lowering of the flash point of the oil (more oil vapors form to be sucked up by the CCV system and possibly form deposits in the intake track and valves). The extra heat generated by turbo charging can exacerbate these problems. There is one study I have read about that indicates if the fuel dilution gets bad enough, it can dissolve the tribological film laid down by the anti wear additive ZDDP. Sounds like Doomsday. You have to wonder why aren't BMWs with the N54 disintegrating all over the place. Must be good metallurgy in those motors.

As owners we can't do much about the design of the N54 but we can focus on the oil. I'm not going to recommend any specific oil, but I can say if your concerned like me you probably ought to change the engine oil frequently and do used oil analysis (UOA) at a good lab (flash point measured under ASTM 93/closed cup, and % fuel dilution measured by gas chromatograph) to figure out the oil change interval (OCI). There are no absolute standards or pass/fail marks for these indicators. Each lab seems to have their own standards and I sometimes wonder if some labs have any pass/fail limits at all. I have seen N54 UOAs posted on BITOG where the oil (the BMW 5w30 factory fill) has sheared back to a 20 wt (in as little as 1500 miles OCI) and no warning or negative comment given by the lab at all. In my opinion an oil should never shear back out of grade; and I'd start to be concerned if % fuel dilution exceeds 2%, and flash point goes much below 375 degrees F. I am frankly wary of BMW's 5w30 oil, and the factory OCI of approx 15000 miles is absurd in a motor like the N54. I would use the best grade synthetic (PAO or ester base stock) I could find and afford, preferably one that meets BMW's LL-01 standard and is in the viscosity range recommended for the N54: 5w30, 5w40, 0w30, or 0w40. And I would do regular UOAs until I could figure out how the oil is performing in my particular style of driving. If your N54 is out of warranty, or you don't care about warranty questions, you can go farther afield. Some folks in the lubricants industry think that part of the answer to di is vegetable-based motor oils, or bio-syns, which appear to stand up to fuel dilution better than conventional synthetics. Others mock these lubes as Mazzola/Canola oils. I do know that Fuchs (a leader in synthetic oils since the 1930s) has recently come out with a bio-syn series of synthetics. Unfortunately, I can't remember the name (Fuchs motor oils aren't available in the U.S.).

Tony, when you get your new rat motor finished you might want to try to communicate with John Rowland, the head chemist with Fuchs, through your Fuchs distributor. He is an avid racer and can be quite forthcoming with advice for individuals using his oils. He may be able to give you some ideas on the best oil for your application.

Sorry for taking so much band width. Hope I didn't go over stuff you already know. By the way, I think the N54 is a dynamite motor and I knew all about the di problems (and the HPFP) before I bought the Z4.