[gorthol]

Originally Posted by edycol

First, you are confusing what is thick and what is thin. That doesn’t have anything with CCP, or 0W or 5W. Thicker or thinner means KV100, or second number.

No I don't. Viscosity of an oil isn't a single number, it's the first before the 0W, which is hugely important for engine tear when cold and also second number which is a different viscosity and then you have the VI which is somewhat of a relation between both.

HTST is only indirectly related to viscosity, it's tearing at temperature and high stresses. It's a good indicator of how the oil bears shearing at extreme conditions but it's not as hugely important as some people think because our engines will very rarely see 150C at that load; the boiling point of the HC-12/LC-18 coolant at a 50% mix is around 130C so if your engine sees 150C the oil shearing is the minor of your problems.

LL01 is LL01! It is based on minimum HTHS and fuel efficiency test which usually limits HTHS at 4cP. It can be ANY grade as long as HTHS falls into those values.

Yes, LL01, the specification, includes many grades. However you said some markets use LL01 with the G20 B48 but in this case not only the specification is required but ALSO a subset of grades. So if the car required LL01 doesn't mean that ALL grades that support the specification will be supported by an specific engine, in this case the G20 B48. You have to match both requirements (grade and spec) not one or the other.

And yes, 10W60 would be fine in your engine. Yes, turbo would spool bit slower, and mpg would take a bit if a hit, but it would be fine.

Oh, sorry, I didn't knew you were a B48 BMW engineer and you had in mind all the tight tolerances of the rod and main bearings and the (some of them very small) oil passages and the required thermo and hydrodynamic rate for these parts and the full graph of the required oil flow at load.

Oil is also acts as a coolant and reducing the flow rate as you can guess is not good for it. For example, it's the main cooling component of the piston heads. And this is done by very precisely "snipping" a spray of oil pointing at the piston head passages when is at bottom dead. Guess what happens to that spray if the oil is too thick.

It's also not good for the oil pump if it was not designed for thicker grades (which it wasn't).

Thicker oil will also stress piston O-rings more leading over time to worse sealing, decreased compression and higher oil consumption.

By the way, people run Redline 15W50 in those engines on track.

If you mean professional teams, they don't have to worry about longevity. However, I think 5W40 is common on at least some teams with the B48. If you mean normal people with their everyday cars, well... people do many things on track differently from the street because it'll be only a few miles but I personally would not run W50 on these engines, even on track. Expensive racing engine oil anyway is usually very different for street one. For one, it usually has a super high ZDDP content that will quickly fuck your cat and OPF filter if used daily (that’s one of the reasons these oils have big “FOR TRACK USE ONLY” warnings on the bottle). It's also tends to have a very high esther and/or AN concentrations in the base which makes it very expensive but also flow and protect the engine better because of the molecular polarity of these bases which tend to "stick" to metals. This means that you could do with a grade higher than spec because even if the hydrodynamic flow is outside the spec, the parts will remain lubricated. This doesn’t happen, or not so much, with group III and even group IV based oils.