Oil shear ?

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If an oil inside a motor shears down a grade is it still protecting at that level or is the oil and add pack compromised to a point where the oil is not lubracating properly?
 
It's still protecting to an extent, but how much is it being ran AFTER it sheared down?

One would need a UOA to know for sure. I personally like oils with higher starting TBN's for this reason.
 
When an oil shears, only the VII polymer shears. The other stuff in the oil (ZDDP, dispersants, detergents, AOs, FMs etc) absolutely doesn't shear. So other than for a drop in viscosity, the oil continues to do what it's supposed to do.
 
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A sheared oil (and by extension, a fuel-diluted oil) is still offering protection, albeit at reduced protection level as a result of reduced oil film thickness consequential upon reduced operating viscosity.
However main bearings and con-rod bearings might predominantly still stays in hydro-dynamic lubrication regimes offering complete protection from abrasion/adhesion wear mechanisms.
Having said this, in the valve train systems and cylinder liner/piston ring tribo-pairs, there is increased levels of unfavourable boundary lubrication and mixed lubrication regimes ...... which are mitigated by essentially functioning anti- wear additive package.
The same cannot be said of gear-train systems, however.
 
Originally Posted By: zeng
A sheared oil (and by extension, a fuel-diluted oil) is still offering protection, albeit at reduced protection level as a result of reduced oil film thickness consequential upon reduced operating viscosity.
However main bearings and con-rod bearings might predominantly still stays in hydro-dynamic lubrication regimes offering complete protection from abrasion/adhesion wear mechanisms.
Having said this, in the valve train systems and cylinder liner/piston ring tribo-pairs, there is increased levels of unfavourable boundary lubrication and mixed lubrication regimes ...... which are mitigated by essentially functioning anti- wear additive package.
The same cannot be said of gear-train systems, however.


So I understand better.

If I am using a 5w40 and it shears to a 30w, then isn't it still offering the same level of protection as a 30w?

If my vehicle manufacturer suggests I should use a Xw40, then aren't they factoring in that Xw40 oils are going to shear?
 
An engineer with a half brain would spec a weight that is acceptable including shear for the duration. Then again a lot of hokey decisions get made by marketing too!

Oil film strength is a function of pressure and viscosity. If you can provide either in sufficient quantities you're doing good. My personal opinion is people who go up a weight to "stay in spec" are over thinking things. Modern engines have tighter tolerances and better oil pumps compared to yore.

I have yet to see an engine wiped out by 20weight oil. You'd think every 2017 model would be stranded on the side of the road.
 
Originally Posted By: DdDd

Oil film strength is a function of pressure and viscosity. If you can provide either in sufficient quantities you're doing good. My personal opinion is people who go up a weight to "stay in spec" are over thinking things. Modern engines have tighter tolerances and better oil pumps compared to yore.



Or more like a "resistance to pressure", right?
 
Originally Posted By: FordCapriDriver
Shearing is the destruction of the viscosity index improvers in an oil, it will cause the oil to get thinner, and it can increase the solid deposits in an engine.


Isn't solid deposits caused more from oil thickening(oxidizing) than shearing?
 
Last edited:
Originally Posted By: tig1
Originally Posted By: FordCapriDriver
Shearing is the destruction of the viscosity index improvers in an oil, it will cause the oil to get thinner, and it can increase the solid deposits in an engine.


Isn't solid deposits caused more from oil thickening(oxidizing) than shearing?

I'm also a bit confused at how shearing increases deposits....I'll await the explanation before further comment.
 
Originally Posted By: DdDd
I have yet to see an engine wiped out by 20weight oil. You'd think every 2017 model would be stranded on the side of the road.


Wiped out vs. just simply excessive wear?

Real world experience seems to back up the advice of these experts too. Some of the best data from the modular community has come from Nick McKinney:

Quote:
"I have said it a few times now, heavier oil has better protection especially in the cam bores. ---I get 2-3 sets of modular heads a week through here, and any lay person just from looking would pick the 500,000 mile cores run on 15W-40 diesel spec all their lives over the typical Mustang head run 50,000 miles on the light stuff"


Fleets typically run their vehicles 250,000 to 500,000 miles! I've heard Nicks experience echoed several times by fleet managers. They wouldn’t run a 5w-20 oil for one minute.
 
Originally Posted By: MotoTribologist
Originally Posted By: tig1
Originally Posted By: FordCapriDriver
Shearing is the destruction of the viscosity index improvers in an oil, it will cause the oil to get thinner, and it can increase the solid deposits in an engine.


Isn't solid deposits caused more from oil thickening(oxidizing) than shearing?

I'm also a bit confused at how shearing increases deposits....I'll await the explanation before further comment.

Well, nowadays it isn't such a problem as modern oils contain less VIIs, and higher quality, more resistant VIIs, but back in the 70s when VII technology was still rudimentary and a lot of multigrade oils were absolutely packed full of them suchas some 10W-40 and 10W-50 mineral oils, when they were destroyed they did form sticky deposits inside engines and caused rings to stick etc etc etc..... or that is atleast what i've read!
 
Originally Posted By: 69GTX
Originally Posted By: DdDd
I have yet to see an engine wiped out by 20weight oil. You'd think every 2017 model would be stranded on the side of the road.


Wiped out vs. just simply excessive wear?

Real world experience seems to back up the advice of these experts too. Some of the best data from the modular community has come from Nick McKinney:

Quote:
"I have said it a few times now, heavier oil has better protection especially in the cam bores. ---I get 2-3 sets of modular heads a week through here, and any lay person just from looking would pick the 500,000 mile cores run on 15W-40 diesel spec all their lives over the typical Mustang head run 50,000 miles on the light stuff"


Fleets typically run their vehicles 250,000 to 500,000 miles! I've heard Nicks experience echoed several times by fleet managers. They wouldn’t run a 5w-20 oil for one minute.



Third party hear-say doesn't count.
smile.gif
 
Last edited:
Originally Posted By: MotoTribologist
Originally Posted By: tig1
Originally Posted By: FordCapriDriver
Shearing is the destruction of the viscosity index improvers in an oil, it will cause the oil to get thinner, and it can increase the solid deposits in an engine.


Isn't solid deposits caused more from oil thickening(oxidizing) than shearing?

I'm also a bit confused at how shearing increases deposits....I'll await the explanation before further comment.


The sheared molecules are left with a less stable bond structure at the shear point. They are susceptible to oxidation at that point. The sheared VII molecules readily oxidize to "sludge".

Ed
 
Originally Posted By: edhackett
Originally Posted By: MotoTribologist
Originally Posted By: tig1
Originally Posted By: FordCapriDriver
Shearing is the destruction of the viscosity index improvers in an oil, it will cause the oil to get thinner, and it can increase the solid deposits in an engine.


Isn't solid deposits caused more from oil thickening(oxidizing) than shearing?

I'm also a bit confused at how shearing increases deposits....I'll await the explanation before further comment.


The sheared molecules are left with a less stable bond structure at the shear point. They are susceptible to oxidation at that point. The sheared VII molecules readily oxidize to "sludge".

Ed



It's a nice theory but sadly not true. VII polymers are routinely and deliberately sheared down in a mechanical grinder either to convert them from a solid bale to a liquid solution or to convert them from a high to a lower SSI rating. The resultant sheared down polymers are just as resistant to oxidation as the starting material.

Most oil oxidation results from the interaction between oxygen and base oil; specifically where oxygen unzips benzylic C-H bonds.
 
Originally Posted By: DdDd
Oil film strength is a function of pressure and viscosity. If you can provide either in sufficient quantities you're doing good.


Which pressure are you stating improves "film strength"...and what are you defining AS "film strength".

Viscosity raises Minimum oil film thickness...pressure doesn't...
 
Originally Posted By: Shannow
Originally Posted By: DdDd
Oil film strength is a function of pressure and viscosity. If you can provide either in sufficient quantities you're doing good.


Which pressure are you stating improves "film strength"...and what are you defining AS "film strength".

Viscosity raises Minimum oil film thickness...pressure doesn't...
Pressure absolutely does raise it. Velocity.
 
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