0W20 vs 5W30 in 1999 E46 323i

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Oil pressure tells you NOTHING about the minimum oil film thickness on the loaded side of the bearing. Manufacturer's don't specify minimum oil pressures for the selection of lubricants, it's to indicate when things are mechanically wrong and need attention.
 
Originally Posted By: Shannow
You don't know, I don't know, and CATERHAM doesn't know where on the curve the BMW engineers set their operational parameters...
I can make an argument that BMW doesn't know either. Only people with "oil on the brain" would think that an engine is designed to an oil. I think they design an engine to be as powerful as possible but within the constraints of being as compact as possible so it can fit in a small sports car. Two inch wide bearings do not fall in line with that philosophy. The bearings may last forever but the engine will be too long and heavy.
 
Originally Posted By: Shannow
Oil pressure tells you NOTHING about the minimum oil film thickness on the loaded side of the bearing.
Which side of the bearing is loaded? In a 60deg, 90deg or opposing design? It's dynamic. To think that you are somewhere on that curve in a steady state condition and it's by design is naïve.
 
Never said that it was static. Stribeck works in dynamic situations, but you also have additional effects like squeeze film come into play. And in all of those scenarios, with bearing parameters, BMEP, engine speed fixed, lower viscosity ALWAYS reduces MOFT.
 
Originally Posted By: Shannow
And in all of those scenarios, with bearing parameters, BMEP, engine speed fixed, lower viscosity ALWAYS reduces MOFT.
That's quite a mouthful there professor. Can you expand on that?
 
Originally Posted By: virginoil
Originally Posted By: Nickdfresh
Originally Posted By: BigmanXD
Hello everyone I'm brand new to the forum and ................ and coming to the conclusion that thinner oil is better especially after reading http://www.bobistheoilguy.com/motor-oil-105/ I'm still unsure about it. .......................... running a 0W20 in a car that the owners manual recommends a synthetic 5W30. Bigman
The misunderstandings... Again, Haas never said "thinner was (always) better". I believe he was only talking about new or newer engines, Haas actually recommended thicker viscosity in aging, higher mileage engines...
Regardless what our Doc H. or BITOG Uni 101????? recommends its the vehicle manufacturers recommendation for the thinnest grade that should be adhered to and your reference manual IMO. The Doc conducts UOAs liaises with manufacturer and in my view is a unique example perhaps not for others to follow unless you are prepared to follow the same regime ie UOA record monitor, liaise with industry etc. Departure from OEM guidelines should be on a case by case basis by the owner rather than imply the experience of some individuals practice is acceptable across the board. I think I need to take break I am getting tired of repeating myself with references back OEM ..............
I how many guys out there read the BITOG oil university and immediately run out to get 0W20.
 
Originally Posted By: turtlevette
Originally Posted By: Shannow
And in all of those scenarios, with bearing parameters, BMEP, engine speed fixed, lower viscosity ALWAYS reduces MOFT.
That's quite a mouthful there professor. Can you expand on that?
peer to peer, which bit don't you get ?
 
Originally Posted By: camrydriver111
Originally Posted By: virginoil
Originally Posted By: Nickdfresh
Originally Posted By: BigmanXD
Hello everyone I'm brand new to the forum and ................ and coming to the conclusion that thinner oil is better especially after reading http://www.bobistheoilguy.com/motor-oil-105/ I'm still unsure about it. .......................... running a 0W20 in a car that the owners manual recommends a synthetic 5W30. Bigman
The misunderstandings... Again, Haas never said "thinner was (always) better". I believe he was only talking about new or newer engines, Haas actually recommended thicker viscosity in aging, higher mileage engines...
Regardless what our Doc H. or BITOG Uni 101????? recommends its the vehicle manufacturers recommendation for the thinnest grade that should be adhered to and your reference manual IMO. The Doc conducts UOAs liaises with manufacturer and in my view is a unique example perhaps not for others to follow unless you are prepared to follow the same regime ie UOA record monitor, liaise with industry etc. Departure from OEM guidelines should be on a case by case basis by the owner rather than imply the experience of some individuals practice is acceptable across the board. I think I need to take break I am getting tired of repeating myself with references back OEM ..............
I how many guys out there read the BITOG oil university and immediately run out to get 0W20.
Exactly. They do just what the OP has done, ask questions. And in that regard Ali Haas' piece has served it's introductory purpose. From that point on, "the devil's in the details", which is what's being discussed here.
 
Originally Posted By: Shannow
peer to peer, which bit don't you get ?
Providing a peer review of your statement as requested, I have a few comments. 1. Is the viscosity vs MOFT relationship linear? I suspect not. I further suspect that there are diminishing returns as viscosity is increased and there may be a breakdown in film thickness at some point and may be based on rate of relative motion between surfaces. 2. Is the viscosity vs MOFT independent of fluid structure? I also suspect not. This makes your statement broadly overreaching. Will longer molecules or other special molecules provide a more robust film, providing in turn a better MOFT vs viscosity relationship. Putting it simpler, a 0W-20 of superior makeup provides a better MOFT than a more standard makeup 0W-30 We'll start with these two and depending upon your answers I may have more comments.
 
Originally Posted By: Shannow
Problem is that you can't absolutely predict what's going to happen through the OCI...it may one day be called upon to drive across the continent to attend a funeral, when the orignal "duty" was 2 mile commutes in the cold.
That's certainly true, unless one were my mother, whose Galaxie only went 10-12 blocks at a time in the winter, with other vehicles relegated to winter highway duty. In the summer, of course, that was a different story. In your scenario, an appropriate, approved viscosity would be more sensible.
 
Originally Posted By: turtlevette
Originally Posted By: Shannow
peer to peer, which bit don't you get ?
Providing a peer review of your statement as requested, I have a few comments. 1. Is the viscosity vs MOFT relationship linear? I suspect not. I further suspect that there are diminishing returns as viscosity is increased and there may be a breakdown in film thickness at some point and may be based on rate of relative motion between surfaces. 2. Is the viscosity vs MOFT independent of fluid structure? I also suspect not. This makes your statement broadly overreaching. Will longer molecules or other special molecules provide a more robust film, providing in turn a better MOFT vs viscosity relationship. Putting it simpler, a 0W-20 of superior makeup provides a better MOFT than a more standard makeup 0W-30 We'll start with these two and depending upon your answers I may have more comments.
Turtlevette, you need to dig out your texts and re-read them...would help you on the path of not having to "suspect" that things are true, by understanding them. The oil film thickness is massive compared to the length of the lubricant molecules. http://papers.sae.org/831689/
Quote:
The minimum oil-film thickness in the front main bearing of a 3.8 L, V-6 engine was measured at 3 000 r/min, and 140 N·m using an electrical resistance technique. For a series of seven Newtonian, single-grade oils, film thickness correlated with oil viscosity measured either in a kinematic or in a high-shear-rate viscometer. For a series of fifteen polymer-containing, non-Newtonian, multigrade oils, however, no single measure of viscosity adequately correlated with film thickness for all of the oils. By eliminating four multigrade oils from the combined single and multigrade data sets, it was possible to correlate film thickness to the viscosity (of the remaining multigrade and Newtonian oils) measured at 150°C and 5 × 10 5 s −1 , conditions which are believed to be representative of temperatures and shear rates in bearing oil films. Possible explanations for the lack of correlation with the entire set of twenty-two oils are discussed.
 
Originally Posted By: Shannow
Oil pressure tells you NOTHING about the minimum oil film thickness on the loaded side of the bearing. Manufacturer's don't specify minimum oil pressures for the selection of lubricants, it's to indicate when things are mechanically wrong and need attention.
Your lack of practical experience is showing here as you really are over thinking this. We need not be concerned at all about MOFT. All one need know is what's the minimum safe operational viscosity (a proxy for which is minimum oil pressure) under extreme WOT conditions and the engine manufacturer/tuner will have that info acquired through experience. Getting this info is not always easy so the fall back info is the manufacturer's test oil pressure spec's. You're correct regarding the main purpose of these test spec's but they are still very useful. These measurements are taken at low normal oil temp's. BMW doesn't reference an oil temp' at which the test is to be taken but for example Porsche does and it's 80C. One can use these minimum OP values as a proxy for a conservative minimum operating viscosity. It's conservative because with the spec' oil it is usually easy to have lower OP than the test spec' at high but still acceptable oil temp's.
 
Originally Posted By: Shannow
however, no single measure of viscosity adequately correlated with film thickness for all of the oils. By eliminating four multigrade oils from the combined single and multigrade data sets, it was possible to correlate film thickness to the viscosity (of the remaining multigrade and Newtonian oils)
So they played with the study until they got results they wanted? This proves my point. Thank you. How are reading my old EE textbooks going to help me with oil discussions?
 
You have moved from having a discussion to being ridiculous.
Originally Posted By: turtlevette
So they played with the study until they got results they wanted? This proves my point. Thank you.
 
Originally Posted By: Shannow
The oil film thickness is massive compared to the length of the lubricant molecules.
That does not mean that a special molecule could not provide the same film thickness at a lower viscosity. You disagree with that? The study you posted seems to elude to that. But they eliminated the tests because it did not fit their frame of reference.
 
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For the record...again...as I've stated every time you wheel this out. * It's not my car, it's another member's car...posting a UOA is neither recommendation, nor endorsement...feel free to point out how harmful the use of that oil was if you like. * I neither run, nor recommend 50s to anyone in the V-6s (in spite of it being Holden's recommendation); * in fact I don't run 50s, full stop (unless you want to pick on the 40 blend in my sig as having 50 in it) Now are you saying that thicker oils DON'T provide thicker MOFT ?
 
Originally Posted By: Shannow
Originally Posted By: CATERHAM
Originally Posted By: Garak
Well, if I was driving it from a cold start for about a mile, and then shutting it down for hours, and repeating, I'm sure a 20 grade would be harmless. Outside of that, stick with something of specified viscosity.
Better than "harmless", it would provide superior lubrication.
OK, define "superior" References ? Any evidence of this in industry standard wear tests like the sequence IVA ?
While you are going back through the posts, you keep missing this one.
 
A special molecule could cure world hunger too, or did you just pull that idea out of your... hat?
Originally Posted By: turtlevette
That does not mean that a special molecule could not provide the same film thickness at a lower viscosity. You disagree with that? The study you posted seems to elude to that. But they eliminated the tests because it did not fit their frame of reference.
 
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