Oil Shearing

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Okay a topic for discussion. The UOA's on several oils show them shearing down in grade, depending on use and application. The general consenses seems to be that shearing is bad. My specific question is do we have any evidence that shearing = sludge, deposits or other problems? Also as as note, I was checking Redline 5w-40 UOAs and found that the thicknesses were 13.8, 14.6, 15.3 used compared to 15.6, any idea why the variance. Thanks Cary
 

MolaKule

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Variances? Different labs, different driving conditions, different engine types, weather, etc. With conventional oils, most of the shearing is due to the VII's (large molecules of polymers), and they do contribute to sludge, where secondary shearing is done on the oil. As Patman said, they eventually become "'useless' molecules." (At least he didn't say, "Useless MolaKules [Big Grin] ). Some of the more upper tier synthetics use little if any VII's, and their shear resistance is very good, mostly due to the shear stability of the base oil. Any polymer or additive molecule that decomposes wants to "polymerize" with the rest of the sludge particles and agglomerate. This is where the DD package comes into play; break them up and hold them in suspension until drained.
 

Cary

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quote:
Originally posted by MolaKule: Some of the more upper tier synthetics use little if any VII's, and their shear resistance is very good, mostly due to the shear stability of the base oil.
Thanks for the Answer. How do we explain the shearing in the M1 0w-40 then? Should we be conserned about deposits?
 

Patman

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quote:
Originally posted by Cary:
quote:
Originally posted by MolaKule: Some of the more upper tier synthetics use little if any VII's, and their shear resistance is very good, mostly due to the shear stability of the base oil.
Thanks for the Answer. How do we explain the shearing in the M1 0w-40 then?

Because it's not an upper tier synthetic! Seriously, any oil that is 14.4 cst at 100c but only turns in a 3.6 HTHS, isn't all that fabulous. Pennzoil 10w40, at 1/4 the cost, has a better HTHS than M1 0w40 does. (I know HTHS isn't the be all end all of a motor oil, but to have such a poor rating for an oil that claims that "nothing outperforms Mobil 1", is pretty sad, IMHO) My guess is that M1 0w40 is just loaded with VII, which is why it thins out so easily. I don't think their base oil is anything special, otherwise they would've been able to create this oil with less VII in it. They probably just took the same base oil they use for their 0w30, and loaded it up with polymers. That also might explain why it's 40C viscosity is rather thick for a 0w oil (at over 80cst) [ August 11, 2003, 02:55 PM: Message edited by: Patman ]
 

MolaKule

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Some of the more shear-stable VII's will "bounce-back' and actually show some viscosity increases later on during the interval, assuming the thickening is NOT due to oxidation. Concerned? Not really, and not as long as the oil is changed before the decomposition products finally overcome the DD adds.
 

Jay

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Patman, Mobil 1 0w-40 is an upper-tier synthetic. It has a HTHS of 3.6 by design. Mobil 1's oil formulation philosophy since their first synthetic oil has been to favor gas mileage. Mobil 1 wants their customers to see better gas mileage with their oils than competing brands. Their HTHS viscosities are a feature not a flaw. [ August 11, 2003, 04:13 PM: Message edited by: Jay ]
 

Patman

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If M1 0w40 is so good, why does it thin out so easily? I can't see any oil maker purposely designing an oil so that it thins out of grade in such a short period of time. If I purchase a 0w40 oil, I want it to remain a 40wt oil, but yet we've seen this oil thin out of grade in relatively short intervals. I'm sorry, but from an oil company as large as them, they could produce something much better than this. They've got the resources, they just choose not to fully utilize them. Mobil 1 must know that the people who use their 0w40 don't care about gas mileage, otherwise they'd use a 5w30. [ August 11, 2003, 04:39 PM: Message edited by: Patman ]
 
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I think any large-spectrum oil will thin out (eg. 0-40, 5-50, etc.)...and that the lower the molecular weight base oil, the more it will thin...ie. a 0-40 will thin more than a 10-50 even though they both have a spread of 40. Furthermore, such oils will tend to have a lower HT/HS than comparable higher molecular weight oils of similar viscosity...ie. a 0-40 will tend to have a lower HT/HS than a 5-40 or 10-40. Does it matter? It would only matter to me if the HT/HS fell below 3.5. Doesn't the A3 rating account for this in their qualification tests? Does shearing make oils less stable/oxidize quicker? When sheared, does this make them more vulnerable to cooking/coking and leading to varnish and sludge formation? I think that's an engine specific answer. Certainly, oil breaking down is not a good thing. I think that synthetics have a better time getting out the tailpipe (consumption) than cooking in your engine and this may contribute to the diminished sludge seen with synthetics.
 
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quote:
Is there any particular reason why an HT/HS of 3.5 is used as the threshold/benchmark of a good oil. Does it depend on the engine the oil is used in or is it an generally acceptable standard.
It just plain depends on the engine design. My engine happens to require an oil with an HTHS of 3.5 or better.
 
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