oil shearing - dino vs. synthetic

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blackhondaccord

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just to clearify the shearing discussions,
in many forum discussions it is commonly stated that 5w30 dino oils shear down to 5w20 or close to it ,
is this also true for full 5w30 synthetics ?
do they shear down also ?
or are synthetics more robust ,and do not shear down ?
and why is it that 5w20 dinos are considered more robust ?
can anyone shed some light on this without getting to tachnical regards
 
syns have less VII whiich is what shears down.
BUT there are good VII and bad ones the good ones shear less.
bruce
 
quote:
in many forum discussions it is commonly stated that 5w30 dino oils shear down to 5w20 or close to it
Click to expand...
The older 5W30 dino oils. Not so much with the newer ones.

quote:
is this also true for full 5w30 synthetics ?
Click to expand...
As stated by Bruce. Grp VII oil is added to increase the range of multiweight oils. However, a plain synthetic oil will not require as much grp VII oil to meet the multiweight specs. It takes more GRP VII to make a 5W30 than a 10W30. Some Syn 10W30 oils do not require any GRP VII so, yes they shear less.

quote:
or are synthetics more robust ,and do not shear down ?
Click to expand...
They generally shear less than the same weight of a dino.

quote:
and why is it that 5w20 dinos are considered more robust ?
Click to expand...
I believe all 5W20 oils are syn blends in order to meet the API SM specs. They generally have more additives than a 5W30 oil to meet the API specs. So, some say they are more robust.

Take this FWIW, I am just regurgitating what I have learned here.
 
A couple of clarifications -

VII stands for "Viscosity Index Improver"...basically polymers that keep the oil from thinning so much as it heats up. Enables multiviscosity performance. And yes, the lower the capability of the base stock and the higher the spread, the more VII polymers would need to be added...more to shear. A synthetic basestock would need fewer VIIs added because it naturally resists thinning when heated to a greater degree (a higher natural viscosity index).

5w-20 oils are considered more 'robust' in part because they are required to pass a double-length test (I forget which sequence) to meet the Ford requirements. As far as having more additives, I'm not sure...but they definitely have high quality basestocks to pass the tests.
 
The newer 5W-30 oils that we have seen on here shear down to 8.5 to9.0 cSt. in a couple thousand miles. (Thats a high 20 to low 30 wt) 5W-30 Mobil 1 doesn't shear. In general 5W-20's (syn and dino/GroupIII) don't shear.
 
Oil does have to shear a little, even a very good oil, to do it's job. Does a 5w-20 shear less than a 5w-30 because there is less viscosity to shear?
 
I thought there was all this talk of these modern SM oils were much better that the old oils, but if 5w30 still sheers then we should stick with 10w30.

Group VII means it is all viscosity index improver, like filling your crankcase with STP Oil Treatment.
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