Quote:
Originally Posted by F87source
Like I said, doing something is better than nothing, and for a cheap part why not. In terms of breaking, that is the reason why one should opt for a quality drain plug instead of going for the cheapest one there is.
That's the problem with the new B58's, to meet fuel efficency standards they are now forcing the B58 to use FE low viscosity oils. Now this is not to be misinterpreted to higher weight being better, but it is to do with shear strength - HTHS, and FE oils typically do not fare well when it comes to shear strength and thus protection is compromised. There are hypothesis out there saying this is what has lead to n55's having bearing failures vs. the n54 which shares a very similar bearing compound, because ll01FE was introduced right at the same time as the n55's release. So honestly the FE specified oils, are a huge negative and if I were a B58 owner I would instantly dump the FE certified oil right after warranty ends for more robust certifications like porsche A40, MB229.5 and BMW LL01. There has also been discussions on BITOG by experts with oil, and with UOA's to back this up, FE oils are inferior to non FE oils.
Also if you use a good base stock oil, a 40 weight oil will have the same viscosity as a thick 30 weight oil, but also have a higher shear strength. That's the benefit of a quality base stock, better shear strength without the viscosity penalty to get it.
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The B58 engine was designed around a 0w20 oil with 0w30 permitted, a Xw40 oil may well present problems in engine longevity due to higher oil temperatures and lower flow rates when expected under stress due to higher pumping pressures than expected. I'm sure BMW didn't do any testing with Xw40 oils, so it is user testing only for any long term effects. The bearing clearances, area and oil passage sizes are going to be designed around using a 0w20 oil for a long period (up to 2 years between oil changes in BMWs in Europe)
I have direct experience of what happens with using an oil grade with a higher viscocity than is optimum.
My car that is generally used on the track is a Caterham R400. It has a Ford 2.0 Duratec that is derived from the standard engines that generally produce form 125-150bhp, rev to 6,500-6,800RPM or so and use 5w30 oil as standard. Caterham keeps the basic engine layout and upgrades parts as necessary (such as forged pistons), but the oiling and cooling design within the block and head and the bearing clearances remain the same. The version I have produces 210bhp naturally aspirated and revs to 7,800rpm and the highest output version produces 256bhp and revs to 8,500RPM.
The recommended oil for the 256bhp engine version to cope with a 8,500RPM redline is 5w50 to purely deal with very high big-end bearing loads at the redline (this is an over-square engine with F1-like pistons speeds). If I run 5w50 oil instead of 0w40, I end up with 10C higher oil temps measured before the oil cooler on track due to lower oil flow (with it being dry sumped, the oil tank temp is much lower and returned to a stable value by the oil cooler) and consistently 1 bar (15 PSI) higher oil pressure including 3.5 bar (51PSI) at idle, leading to the oil pressure relief valve activating at 6 bar (88PSI) at around 4,500RPM instead of around 6,000RPM on the 0w40 oil. The higher output engine is advised to have a 50,000km / 30,000 mile rebuild in normal use due to general wear, my 210bhp has no advised rebuild interval.
The bottom line is use the thickest oil necessary to provide big-end protection at the hottest oil temp allowed at redline. The B58 going by worldwide reputation as a solid and reliable engine, is fine with a 0w20 oil with stock redline and max oil temp, but using 0w30 if run flat out is also supported. Anything thicker is into user test territory, with potentially negative effects from reduced oil flow and higher oil temperatures at the bearings, with no appreciable benefit.