Originally Posted By: alarmguy
Originally Posted By: DoubleWasp
Originally Posted By: alarmguy
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Shearing is when a 40 weight oil "shears" down to a 30 weight oil ect.
However its meaningless to judge an oil on shearing only, more so in a forum without any proof, a UOA and the engine make and model.
Just hearsay but no factual helpful information as far as your particular vehicle, your vehicle engine design and type of use is responsible how much your oil shears but some will look towards an oil to help make up for engine design and some oils will be better to handle it, in theory ...
So I question any post that states any particular oil shears easy, even more so when an oil states it is designed to be more shear stable..
Shear to 20wt:
http://forum.chaparralboats.com/index.php?/topic/17412-mercruiser-25w40-used-oil-analysis/
Quote:
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Here is the quick summary of results:
All wear metals are approximately the same regardless of the oil in use, within test variances.
All final TBN values are strong, ranging from 4 to about 5.5, so plenty of additive left after a season.
All oils sheered to some extent, but the Mercruiser branded oil sheered from a 40 to a 20, and all others sheered from a 40 to a 30.
This is VERY typical on the small blocks which typically have little or no oil cooler.
Whats shearing is the oil itself. VI is not necessary for this to happen.
Marketing is a lot different than what goes on in the field.
1. Nothing in this post (and UOA) indicates shearing, one would need to see the actual UOA since this one is missing information, such as fuel and why, seeing actual test results are far better.
2. Can not rely on 1 hand typed UOA from one owner as fact.
Just not enough VOAs and UOAs on this oil, even the boron and mag doesnt seem to add up and without current info not possible to know.
3. I do know one thing, MANY years ago my brother put Castrol 20w50 in his 30 foot Searay with Twin V-6 engines instead of his usual 25/40 merc oil, figures it would be just as good and much cheaper.
Well, after a run out into the ocean, once back at his home, the engines sounded like a bucket of bolts with the valves clapping and he changed it out back to Merc. My brother, not really into this stuff like I am, was bewildered at the difference running the Castrol and how noisy the engine was.
4. Due to lack of UOAs on this oil, not possible to be sure but the UOA you posted, the make up of the oil doenst seem right either.
But here is a UOA from almost 14 years ago with MASSIVE fuel dulation and still higher viscosity then the one posted above where the person left out that informatio.
Without knowing fuel dilution its not possible to take the viscosity of any UOA serious and I am wondering why the person left it out ... here is one with it in.
Click 25w40 Merc oil
5. Another with less fuel but still alot ...
Click, still in grade
1. I'm not seeing any evidence that what the oil was 14 years ago is what it is now.
2. I never said anything about Castrol 20w50.
3. I have more, complete UOA's of this oil shearing without significant fuel dilution that I will be posting.
4. 21 whole hours and still in grade? Wow! what an amazing feat!