Straight Grades more Shear Stable than Multi's?

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1,151
Location
Clovis, CA
Seems like I read on here somewhere that straight grades were less prone to shear out of grade than multi-viscosity oils. I also recall reading on here that straight grades have a really high pour point when cold and that you don't want to use them during winter. Is any of this true?
 
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8,937
Location
SC
All things being equal, a straight grade oil will be more shear stable than a multi-grade. As for pour point, it depends on the grade and the quality of the base oil. Amsoil's straight 30 wt made from PAO has a very low pour point. A typical mineral based 30 wt may have what appears to be a low pour point, but its cold cranking viscosity will be very, very high. Back when auto makers would list straight grades in the owners manual as well as multi-grades, 32F was usually listed as the lowest temp in which 30 wt should be used. Colder than that, and you'd go to 20w or 10w or 5w straight grades, depending how cold you expected it to be before the next oil change.
 

JHZR2

Staff member
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46,257
Location
New Jersey
Yes, all of that has been well established long ago. IMO, other than air cooled lawn equipment, it doesnt hold much necessity any longer. So many things have been run so long on 15w-40 and 10w-30 oils especially, for super long lives, that I would use with confidence. Consider Amsoil ACD if you want the best of all worlds. JMH
 
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3,491
Location
Millbrae, CA
'I think one problem with straight weights is that a SAE 30 will get thinner above 100C than will a sheer stable 10w30. So if you overheat a multigrade may be better?" Paul generally not true the if the straight wt and multi have the same vis at 100C the straight should have a higher HTHS than the same vis multi. BUT there could be are some straight wt's that that are say 10.0 at 100C and some multi's that are 12.1 and then yes the multi will have a higher HTHS vis even with some shearing. bruce
 
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13,132
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By Detroit
One of the most sheer stable PCMO oils available is Redline. I understand that all but the 5w40 Redline is without VIIs and so, in effect, is straight weight, albeit meeting the multiviscosity grades. I think one problem with straight weights is that a SAE 30 will get thinner above 100C than will a sheer stable 10w30. So if you overheat a multigrade may be better?
 
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