Using 0W40 = more oil flow is false

[swamp2]

Originally Posted by regular guy

Let's recap.

• SFP says the S65 is optimized FOR 10W60 in post-45.
• RG takes issue with that and asks for proof -- even theoretical proof.
• Swamp takes issue with RG for taking issue with SFP.
• Swamp says "(he doesn't) see the point of any skepticism of this claim by SFP."
• So RG asks swamp the same question RG asked SFP and asks swamp for the same type of proof.
• Swamp doesn't like the question and immediately reframes it. The question changes from S65 optimized FOR 10W60 to S65 optimized WITH 10W60.
• In doing so, swamp agrees with RG but starts an argument to show that we are in violent agreement that SFP's comments don't make sense that the S65 being optimized FOR 10W60.
• Swamp proclaims the S65 oil system is robust enough to tolerate thinner oil viscosities.
• Swamp announces he has switched to 0W40 oil.

If I got that wrong, I'm sure I'll get corrected...and that correction will look like a disagreement even if it isn't.

I think you've got this largely correct, except:

• My original interpretation of SFPs post was, what I have been arguing all along, that both components and the entire lubrication system had some engineering optimization done by BMW M (perhaps also at the time the S85 was developed - thanks BMRLVR for that astounding insight that I wasn't aware of...S65 is a derivative engine, of the S85, really...) and that one or more of the oil properties going into those analyses are based on the properties of the original single factory specified 10W-60 TWS oil. This is what I mean/meant by "WITH".
• You've obviously backed away from your claim that my claim of such sorts of activity being pretty well common place (love the apropos SFP quote "M engineers having legandary[sic] arse finding problems").
• I've been absolutely up front from the first hint of any disagreement on this topic that any reasonable lubrication system should/would be robust to such a change from 10W-60 to 0W-40. Perhaps in some small way movement from "optimal" for some conditions may be compromised with improvements possible under others conditions with such a change. There's no such thing as a free lunch... If 0W-40 is both better in every regard and less expensive, it sure would have been great to spec it originally. Oh yeah, I forgot about the BMW-Castrol conspiracy...
• Last but not least I "announced" that I switched to 0W-40 quite a long time ago. I've always maintained that this change seems to pass an engineering sanity check appeal for potential to help what may be a rare occurrence with little if any downside. It seems like cheap insurance and lowers oil bills at the same time. Why not change? It certainly doesn't mean I can't continue to disagree with extremist points of view that BMW M completely "royally" screwed all of the crank bearing clearances (and just for clarification/separation, no I am not claiming this is your claim). Let's again note that the newer 702/703 bearings are WITHIN Clevite specification for clearance...
• Now do I actually believe that by some impossible feat if the S65 was developed identically to it's state now, but BMW had mandated 0W-40 that we would "magically" be experiencing zero bearing related issues in the car. No, I positively don't believe that. Might we experience a bit fewer of them. Who knows, maybe.

[SenorFunkyPants]

Originally Posted by regular guy

What does it mean to optimize the "lubrication system" for 10W60 and what changes would be required to change to 0W40?

You rarely ask a question when you don't know the answer so wouldn't it just be easier to point out where you think I am wrong and we can go from there?
Anyway in summary:
There seems to be broad agreement in this thread that a thinner oil would give a higher flow rate (all else being equal).
You yourself have stated that a higher flow rate would give better cooling to the bearings.
So is it not fair to say that there would be an optimum oil flow rate target to aim for when designing a new lubrication system and that adjusting the output of the volume flow-controlled hinged-valve oil pump could help you achieve that target? And if you could not reach that target with a 10W60 oil would it not make sense to use a lighter weight oil?
Having decided to use the TWS, as part of the new lubrication system design process would you not optimise the design wherever possible to produce the flow/pressure/temp targets you had initially set?

Why did the M Division stick with the TWS 10W60 weight oil?
Cost:
Its one of the most expensive oils that Castrol produce so its definitely not about the free maintenance costs.
Poor reliability equals high warranty costs, so you wouldn't choose an oil that gave poor reliability.
OCI:
Most any fully synthetic oil can be formulated for long oil change intervals...the Mobil1 EP range is guaranteed for 15K miles so its not about long OCIs.
Marketing:
There is almost no marketing value to Castrol in having "Exclusive approval for use in M Engines" on the TWS packaging when so few retailers stock it. Castrol's marketing department will be much happier with the the M Divisions move to Castrol Edge Professional 5W30, a far more mainstream and marketable oil.
Efficiency:
Heavier weight oils "consume" more power than lighter weight oils and penalises mpg. So BMW gave away BHP and fuel consumption when deciding on the TWS.
Yet despite all these negatives BMW stuck with the TWS.

As Swamp has noted, there are compromises to make when designing an engine and choosing an oil to use with it, but when prioritizing those compromises, high reliability with lost cost are going to be at/near the top of the list.
Maybe with this particular high rev'ing, high specific output engine design the (quite decent) reliability is as good as it gets and no amount of tinkering with oil weight and bearing clearance is going to make it any better.

[kawasaki00]

Originally Posted by swamp2

It's clearly only a real troll who falsely thows that accusation at other respectable forum members who are discussing/debating politely and in good faith. Shame on you, regardless of if you were pointing your finger at me or at SFP.

I was actually against the entire thread because the entire thing was botched from the get go.
If I wanted to direct it toward you I would have quoted you. But hey whatever.

[kawasaki00]

Originally Posted by swamp2

Let's again note that the newer 702/703 bearings are WITHIN Clevite specification for clearance...[*]Now do I actually believe that by some impossible feat if the S65 was developed identically to it's state now, but BMW had mandated 0W-40 that we would "magically" be experiencing zero bearing related issues in the car. No, I positively don't believe that. Might we experience a bit fewer of them. Who knows, maybe.[/LIST]

Although this is true that is only half the equation. When they are that tight even within spec they need to be pared with a thinner oil to maintain lubrication.

[regular guy]

Originally Posted by swamp2

I think you've got this largely correct, except:

• My original interpretation of SFPs post was, what I have been arguing all along, that both components and the entire lubrication system had some engineering optimization done by BMW M (perhaps also at the time the S85 was developed - thanks BMRLVR for that astounding insight that I wasn't aware of...S65 is a derivative engine, of the S85, really...) and that one or more of the oil properties going into those analyses are based on the properties of the original single factory specified 10W-60 TWS oil. This is what I mean/meant by "WITH".
• You've obviously backed away from your claim that my claim of such sorts of activity being pretty well common place (love the apropos SFP quote "M engineers having legandary[sic] arse finding problems").
• I've been absolutely up front from the first hint of any disagreement on this topic that any reasonable lubrication system should/would be robust to such a change from 10W-60 to 0W-40. Perhaps in some small way movement from "optimal" for some conditions may be compromised with improvements possible under others conditions with such a change. There's no such thing as a free lunch... If 0W-40 is both better in every regard and less expensive, it sure would have been great to spec it originally. Oh yeah, I forgot about the BMW-Castrol conspiracy...
• Last but not least I "announced" that I switched to 0W-40 quite a long time ago. I've always maintained that this change seems to pass an engineering sanity check appeal for potential to help what may be a rare occurrence with little if any downside. It seems like cheap insurance and lowers oil bills at the same time. Why not change? It certainly doesn't mean I can't continue to disagree with extremist points of view that BMW M completely "royally" screwed all of the crank bearing clearances (and just for clarification/separation, no I am not claiming this is your claim). Let's again note that the newer 702/703 bearings are WITHIN Clevite specification for clearance...
• Now do I actually believe that by some impossible feat if the S65 was developed identically to it's state now, but BMW had mandated 0W-40 that we would "magically" be experiencing zero bearing related issues in the car. No, I positively don't believe that. Might we experience a bit fewer of them. Who knows, maybe.

I'm not sure I backed away from anything because I don't recall claiming anything except that SFP's comments don't make sense. But I can see from your last few points that you're changing the subject once again. Sorry swamp, I'm not interested in following. I'll stay on topic and answer SFP instead.

[regular guy]

Originally Posted by SenorFunkyPants

You rarely ask a question when you don't know the answer so wouldn't it just be easier to point out where you think I am wrong and we can go from there?

Before I answer, I'm not sure I've said some of the things you attribute to me (below). I tend to only say things that I can prove or have evidence of. I'm not an oil guy, so some of the comments below don't sound like they came from me.

Now, to address the topic above. Once again, I'm not an oil guy. But here's what goes through my mind when I see somebody say that the S65 "LUBRICATION SYSTEM" is optimized FOR 10W60.

• I'll start with the oil pump, and ask what that means. The oil pump is a variable rate positive displacement pump. As such, it isn't going to behave any differently between 10W60 and 0W40. So that can't be this "optimization" you're talking about.
• Next I thought of the oil galleys, and how they're machined. Maybe 0W40 does have higher flow at the same pressure. Not being an oil guy or fluid dynamics guy, I don't really know. But let's say that it does. So I ask myself, what adjustments would need to be made to keep the oil flow the same through the galleys with 0W40 vs. 10W60. Knowing that the oil galley bore would only differ by a few 0.0001's to make this change, I don't think boring bits come in those increments, so I don't think the oil galleys were optimized for 10W60.
• Next I turned my attention to the oil squirters. OK, so maybe the oil will squirt a little more freely through the oil squirters. In this case, that's a good thing because it means the pistons will get more cooling. So oil squirters are now off the list of components optimized for 10W60.
• Next I thought of the camshaft lubrication. No bearings on the cams, it's direct metal-to-metal contact. More oil flow helps, not hurts here too. So take that off the list of components optimized for 10W60.
• Next let's turn our attention to the VANOS. VANOS is pressure controlled. Thicker oil may result in slower response time, thinner oil may result in faster response time. If the response time changes at all, it would probably only change by a few milliseconds (just a guess). To me, faster response time sounds like a good thing, not a bad thing. So I took VANOS off the list of components optimized for 10W60.
• Next let's look at the various check valves. If I remember correctly, there's six check valves in the engine. The check valves only play a role when the engine is off, not on. They are intended to hold oil in places like cylinder heads and VANOS while the engine is off. I think we can all agree that check valves don't play a role during normal operation and can be taken off of the list of components optimized for 10W60.
• I'm almost out of components and I haven't found anything that could possibly be optimized for 10W60 yet. There's only a few items left -- like the oil filter and bearings. Let's talk about the oil filter first. Could that be this magical component that can truly be optimized for 10W60? Maybe it could...I don't know. Certainly not a smoking gun if it is.
• So that leaves us with bearings. If BMW really optimized the bearing design and clearances for 10W60, then judging by all the photos of failing bearings, they obviously did a bang up job. Maybe this is the one and only component you are talking about. But this is the one area that if left alone could probably BENEFIT from switching to 0W40.

OK, so there's my list and telling you why your comment doesn't even make sense to me. I'm not an oil guy, but I do think about how things work enough to think your comments don't make any sense. So when I'm asking you to explain, it's not because I have the answers...it's because I've gone through all of those items in my mind and can't figure out what, if any of them, could be optimized for 10W60 nor even figure out what that means. So when I'm asking you to explain it, I really want an answer. I guess what I'm really asking of you is to think about it as thoroughly as I have. If I missed something or analyzed it wrong, then let's have a discussion about it. So far, you haven't explained any of it and it still doesn't make sense to me.

Anyway in summary:
There seems to be broad agreement in this thread that a thinner oil would give a higher flow rate (all else being equal).
You yourself have stated that a higher flow rate would give better cooling to the bearings.
So is it not fair to say that there would be an optimum oil flow rate target to aim for when designing a new lubrication system and that adjusting the output of the volume flow-controlled hinged-valve oil pump could help you achieve that target? And if you could not reach that target with a 10W60 oil would it not make sense to use a lighter weight oil?
Having decided to use the TWS, as part of the new lubrication system design process would you not optimise the design wherever possible to produce the flow/pressure/temp targets you had initially set?

Why did the M Division stick with the TWS 10W60 weight oil?
Cost:
Its one of the most expensive oils that Castrol produce so its definitely not about the free maintenance costs.
Poor reliability equals high warranty costs, so you wouldn't choose an oil that gave poor reliability.
OCI:
Most any fully synthetic oil can be formulated for long oil change intervals...the Mobil1 EP range is guaranteed for 15K miles so its not about long OCIs.
Marketing:
There is almost no marketing value to Castrol in having "Exclusive approval for use in M Engines" on the TWS packaging when so few retailers stock it. Castrol's marketing department will be much happier with the the M Divisions move to Castrol Edge Professional 5W30, a far more mainstream and marketable oil.
Efficiency:
Heavier weight oils "consume" more power than lighter weight oils and penalises mpg. So BMW gave away BHP and fuel consumption when deciding on the TWS.
Yet despite all these negatives BMW stuck with the TWS.

As Swamp has noted, there are compromises to make when designing an engine and choosing an oil to use with it, but when prioritizing those compromises, high reliability with lost cost are going to be at/near the top of the list.
Maybe with this particular high rev'ing, high specific output engine design the (quite decent) reliability is as good as it gets and no amount of tinkering with oil weight and bearing clearance is going to make it any better.

[swamp2]

Originally Posted by regular guy

I'm not sure I backed away from anything because I don't recall claiming anything except that SFP's comments don't make sense. But I can see from your last few points that you're changing the subject once again. Sorry swamp, I'm not interested in following. I'll stay on topic and answer SFP instead.

This is a forum to promote discussion. I really fail to see how the subtopic of what techniques are used by OEMs to design and optimize both lubrication components and systems is so off topic. You claimed BMW likely didn't do some type of design/analysis/optimization and I claim they did. It appears you've likely adjusted your opinion on that now, despite a lack of absolutely firm/concrete evidence.

Anyway, a key point in this oil discussion in my mind is the question of the tradeoffs when changing oil. I'm certainly not an oil expert either, however, I think it's a very reasonable conclusion that any (reasonable) oil change (brand/grade/viscosity/etc.) is a natural give and take. Some aspects of engine lubrication performance will be improved but others will suffer. For this particular change say from Castrol TWS 10W-60 to Mobil 0W-40 (LL-01) the overall change in properties is small and I'd expect similar (very) small benefits and detriments.

[regular guy]

Originally Posted by swamp2

This is a forum to promote discussion. I really fail to see how the subtopic of what techniques are used by OEMs to design and optimize both lubrication components and systems is so off topic. You claimed BMW likely didn't do some type of design/analysis/optimization and I claim they did. It appears you've likely adjusted your opinion on that now, despite a lack of absolutely firm/concrete evidence.

Anyway, a key point in this oil discussion in my mind is the question of the tradeoffs when changing oil. I'm certainly not an oil expert either, however, I think it's a very reasonable conclusion that any (reasonable) oil change (brand/grade/viscosity/etc.) is a natural give and take. Some aspects of engine lubrication performance will be improved but others will suffer. For this particular change say from Castrol TWS 10W-60 to Mobil 0W-40 (LL-01) the overall change in properties is small and I'd expect similar (very) small benefits and detriments.

You take too many liberties with the things I say -- or more importantly too many liberties with the things I DON'T say. I'm not interested in proving I did or didn't say something that you claim. End of discussion for me because it's no longer technical. If you want to keep it technical, answer the questions I posed to SFP.

[swamp2]

Originally Posted by regular guy

You take too many liberties with the things I say -- or more importantly too many liberties with the things I DON'T say. I'm not interested in proving I did or didn't say something that you claim. End of discussion for me because it's no longer technical. If you want to keep it technical, answer the questions I posed to SFP.

Yes, sir, right away sir. You take yourself way too seriously sometimes...

Although I don't generally like to answer for others, the borderline ridiculousness of many items in you big bullet point list just above basically scream out for comments and corrections.

Originally Posted by regular guy

But here's what goes through my mind when I see somebody say that the S65 "LUBRICATION SYSTEM" is optimized FOR 10W60.

I don't believe that, never did, but the list below is where more misinformation begins.

In general your naivete here is quite amazing. You and many other folks here have such a fundamental lack of knowledge about the depth and breadth of the art, practice, academics and actual industry practices of automotive engineering it's just astounding. You really don't even know what you don't know and that is a problem in these discussions. Let's get to these FACTS or "keep it technical" as you mention since that is so critical for you to even be involved in the discussion...

Originally Posted by regular guy

• I'll start with the oil pump, and ask what that means. The oil pump is a variable rate positive displacement pump. As such, it isn't going to behave any differently between 10W60 and 0W40. So that can't be this "optimization" you're talking about.

Do you think various forms of optimization for oil pumps doesn't occur? Again, this is something software from my company is routinely used for. Again, is the pump robust across viscosity changes, sure, but at the same time NOMINAL viscosity values are used in the simulations so there is a tacit assumption that the pump is optimized "with" or pehaps even stronger "for" a given oil. Hint: Look look for "μ" perhaps as opposed to the word "viscosity" in many papers as this is the standard variable in physics/engineering for such.

Head to SAE or google and try some searches with various combinations of

"oil", "pump", "optimization", "cfd", "viscosity"

Here is just one good (and free) paper to start, link.

Again, don't be fooled by a particular type of pump. The same engineering attention is given to pumps regardless of major type (gear, gerotor, vane, scroll, etc.) or application (automotive, heavy transport, marine, industrial, etc.). Pumps are a really large and specialized area of industrial engineering and companies are willing to spend a heck of a lot of time and money to squeak out very small marginal improvements in designs because those in turn lead to big consequences for those who buy and use the pumps.

Originally Posted by regular guy

• Next I thought of the oil galleys, and how they're machined. Maybe 0W40 does have higher flow at the same pressure. Not being an oil guy or fluid dynamics guy, I don't really know. But let's say that it does. So I ask myself, what adjustments would need to be made to keep the oil flow the same through the galleys with 0W40 vs. 10W60. Knowing that the oil galley bore would only differ by a few 0.0001's to make this change, I don't think boring bits come in those increments, so I don't think the oil galleys were optimized for 10W60.

First (laminar) flow rate absolutely is dictated by viscosity at a given pressure drop. Basically pressure drop is proportional to viscosity x flow rate. Secondly, you surely don't think the existence of tooling available from someone like McMaster Carr dictates what diameters an OEM will bore into engine components? Please tell me you didn't just write that. When I worked for a small bicycle design/engineering/manufacturing company we routinely (and inexpensively) ordered custom drilling/reaming tooling to the 0.0001"-0.0005" size for a variety of suspension, shock and brake work, both manufacturing and repair/rework. OEMs build to the specification and tolerances determined by the engineer, not to what drill sizes come in a Home Depot inch sized drill bit set...

Originally Posted by regular guy

• Next I turned my attention to the oil squirters. OK, so maybe the oil will squirt a little more freely through the oil squirters. In this case, that's a good thing because it means the pistons will get more cooling. So oil squirters are now off the list of components optimized for 10W60.

Viscosity is of fundamental important to nozzle design and obtaining both desired flow and cooling rates are two of the key aspects of their design, placement and oil use. Have a look at this (SAE technical paper search):

https://www.sae.org/search/?qt=oil+j...cosity&x=0&y=0 ,

or this paper,

"Numerical investigations of piston cooling using oil jet in heavy duty diesel engines", link.

And please don't say the heavy duty diesel thing makes a lick of difference...

Although I didn't bother to do much additional investigation, I suspect there are just as many details you've glossed over for both camshaft lubrication and the way viscosity interacts with the VANOS system.

Originally Posted by regular guy

• So that leaves us with bearings. If BMW really optimized the bearing design and clearances for 10W60, then judging by all the photos of failing bearings, they obviously did a bang up job. Maybe this is the one and only component you are talking about. But this is the one area that if left alone could probably BENEFIT from switching to 0W40.

Yes, pressure, flow rate and viscosity are all key ingredients of bearing tribology as well.

Your conclusion here about the effectiveness of BMWs engineering directly contradicts your prior statements that you agree that observed bearing wear is not a common nor universal problem and also assumes that something as minor as a change to 0W-40 could be a sort of magical fix for this potential problem. Both points are presently completely unknown.

It's worth repeating again and again... Are these components optimized specifically for 10W-60, generally no. Does the viscosity and other properties of the chosen engine oil go directly into the calculations, equations, simulations, optimizations, testing, etc. for all of these lubrication components and systems - RESOUNDINGLY, YES. Are these systems likely quite robust to relatively small changes in viscosity, yes again. Are some results/metrics moved slightly away from optimal or nominal design values and more toward a less desirable state by changing oil viscosity, yes. Are other metrics improved, almost for sure, yes. There certainly is not one oil to rule them all - i.e. there is no globally optimal oil choice. I guess that's probably obvious to most but oftentimes your statements make it sound like it's all or nothing and that is an over simplification.

Thus one word such as "FOR" or "WITH" can not capture the essence nor subtlety of the question.

But either way you slice it you are clearly not totally informed about the depth and breadth to which something like oil viscosity and one particular value of it is "engineered into" a given design.

[regular guy]

That's correct swamp, I'm not an academic and I don't pretend to be; so I'm obviously naive and uninformed when it comes to academic issues and discussions. I spend as much time telling people that I'm not an expert and asking legitimate questions as time you spend telling people about your five master's degrees and pretending to be an expert on everything. So there's quite a bit of irony here in being accused of thinking more highly about myself than is warranted.

But I see from above that you still can't answer without changing and reframing the question from something it's not into something you want it to be for your own agenda. Once again you missed the forest through the trees. And I see you can't even do that without fabricating a false story line and false premise to go along with it. If you're trying to be a teacher, it's not working.

None of my questions were answered. Big surprise.

[BMRLVR]

Originally Posted by swamp2

Yes, sir, right away sir. You take yourself way too seriously sometimes...

Although I don't generally like to answer for others, the borderline ridiculousness of many items in you big bullet point list just above basically scream out for comments and corrections.

I don't believe that, never did, but the list below is where more misinformation begins.

In general your naivete here is quite amazing. You and many other folks here have such a fundamental lack of knowledge about the depth and breadth of the art, practice, academics and actual industry practices of automotive engineering it's just astounding. You really don't even know what you don't know and that is a problem in these discussions. Let's get to these FACTS or "keep it technical" as you mention since that is so critical for you to even be involved in the discussion...

Do you think various forms of optimization for oil pumps doesn't occur? Again, this is something software from my company is routinely used for. Again, is the pump robust across viscosity changes, sure, but at the same time NOMINAL viscosity values are used in the simulations so there is a tacit assumption that the pump is optimized "with" or pehaps even stronger "for" a given oil. Hint: Look look for "μ" perhaps as opposed to the word "viscosity" in many papers as this is the standard variable in physics/engineering for such.

Head to SAE or google and try some searches with various combinations of

"oil", "pump", "optimization", "cfd", "viscosity"

Here is just one good (and free) paper to start, link.

Again, don't be fooled by a particular type of pump. The same engineering attention is given to pumps regardless of major type (gear, gerotor, vane, scroll, etc.) or application (automotive, heavy transport, marine, industrial, etc.). Pumps are a really large and specialized area of industrial engineering and companies are willing to spend a heck of a lot of time and money to squeak out very small marginal improvements in designs because those in turn lead to big consequences for those who buy and use the pumps.

First (laminar) flow rate absolutely is dictated by viscosity at a given pressure drop. Basically pressure drop is proportional to viscosity x flow rate. Secondly, you surely don't think the existence of tooling available from someone like McMaster Carr dictates what diameters an OEM will bore into engine components? Please tell me you didn't just write that. When I worked for a small bicycle design/engineering/manufacturing company we routinely (and inexpensively) ordered custom drilling/reaming tooling to the 0.0001"-0.0005" size for a variety of suspension, shock and brake work, both manufacturing and repair/rework. OEMs build to the specification and tolerances determined by the engineer, not to what drill sizes come in a Home Depot inch sized drill bit set...

Viscosity is of fundamental important to nozzle design and obtaining both desired flow and cooling rates are two of the key aspects of their design, placement and oil use. Have a look at this (SAE technical paper search):

https://www.sae.org/search/?qt=oil+j...cosity&x=0&y=0" rel="" target="_blank">http://<a href="https://www.sae.org/...ty&x=0&y=0</a> ,

or this paper,

"Numerical investigations of piston cooling using oil jet in heavy duty diesel engines", link.

And please don't say the heavy duty diesel thing makes a lick of difference...

Although I didn't bother to do much additional investigation, I suspect there are just as many details you've glossed over for both camshaft lubrication and the way viscosity interacts with the VANOS system.

Yes, pressure, flow rate and viscosity are all key ingredients of bearing tribology as well.

Your conclusion here about the effectiveness of BMWs engineering directly contradicts your prior statements that you agree that observed bearing wear is not a common nor universal problem and also assumes that something as minor as a change to 0W-40 could be a sort of magical fix for this potential problem. Both points are presently completely unknown.

It's worth repeating again and again... Are these components optimized specifically for 10W-60, generally no. Does the viscosity and other properties of the chosen engine oil go directly into the calculations, equations, simulations, optimizations, testing, etc. for all of these lubrication components and systems - RESOUNDINGLY, YES. Are these systems likely quite robust to relatively small changes in viscosity, yes again. Are some results/metrics moved slightly away from optimal or nominal design values and more toward a less desirable state by changing oil viscosity, yes. Are other metrics improved, almost for sure, yes. There certainly is not one oil to rule them all - i.e. there is no globally optimal oil choice. I guess that's probably obvious to most but oftentimes your statements make it sound like it's all or nothing and that is an over simplification.

Thus one word such as "FOR" or "WITH" can not capture the essence nor subtlety of the question.

But either way you slice it you are clearly not totally informed about the depth and breadth to which something like oil viscosity and one particular value of it is "engineered into" a given design.

Holy cow!!!

Let's see where swamp has gone with the oil/rod bearing discussion

First: 10W60 is the only oil one should use in the S65. There is no bearing issue, BMW engineered it this way for a reason.

Second: 0W40 would be ok but I would not use it. Engine was designed around 10W60.

Third: I have switched to 0W40 and feel it may help with the issue (first there was no issue?)

Fourth: The lubrication system is good to handle other viscosities....... But there are both pluses and minuses from using the 0W40.

Are you dizzy? I know my head is spinning!!!

It is quite obvious that you have no idea what to think about the oil and bearing discussions with the S65...... If you did you wouldn't change your mind like I change my socks!