Oil shear ?

[Shannow]

Originally Posted By: bigj_16
Pressure absolutely does raise it. Velocity.


What pressure are you talking about???

MOFT (note, thickness, NOT strength) goes
up with a decrease in applied pressure (load/bearing area)
up with increased viscosity
up with increased surface speed (RPM)
up with reduced bearing clerance for a given shaft diameter.

So which pressure are you two referring to ?

 

[userfriendly]

Peer pressure.

 

[zeng]

MOFT goes up too , with pressure-viscosity coefficient.....
which is a property of (base) oils that co-relates with heavily loaded contact pressure zones but independent of circulating oil pressure, IMHO.

 

[userfriendly]

In one of those 1,000 page essays of cherry picked other people's work, "Mr SAE Paper" had us all read at 4am a couple of years ago, it was mentioned that high oil pressure also raises the boiling point, preventing gas bubbles from reducing the viscosity of the lubricant.

 

[dlundblad]

Originally Posted By: 4WD
Saw a new Ford VelociRaptor today in Houston - I want to be young again


I am sure that thing chews 5w30's down to 5w20's. Then again, I believe the VelicRaptor is super charged. I wonder what oil that thing would require?

The first ecoboosts in the F150 originally required a 5w20. They were then back spec'd to 5w30 for this very reason.

 

[SilverFusion2010]

Originally Posted By: dlundblad
Originally Posted By: 4WD
Saw a new Ford VelociRaptor today in Houston - I want to be young again


I am sure that thing chews 5w30's down to 5w20's. Then again, I believe the VelicRaptor is super charged. I wonder what oil that thing would require?

The first ecoboosts in the F150 originally required a 5w20. They were then back spec'd to 5w30 for this very reason.

I think it's a bigger turbo and ecu programming. The block is very strong, and modders have found that fueling is the limiting factor, not durability

 

[zeng]

Originally Posted By: ArcticDriver
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?

Generally yes.
Having said this, under identical operating parameters, a 5W40 of KV@100*C at say, 11 cSt (post VII shearing and fuel dilution) would offer a lower level of protection in terms of MOFT, comparing against a xW30 (possibly of similar base stocks) of KV@100*C at 11.5 cSt , post shearing and dilution.

Quote:
If my vehicle manufacturer suggests I should use a Xw40, then aren't they factoring in that Xw40 oils are going to shear?

Engineering departments of veh manufacturers , not sure about marketing departments though ( of whom I never trust), would've considered the normal phenomena of viscosity shearing, fuel dilution, high-temperature and high-load environments etc. Though administrative CAFE requirements could have swayed their evaluations, as dictated by finance departments.

 

[Shannow]

HTHS loss is about half the percentage KV loss...

 

[edhackett]

Originally Posted By: SonofJoe

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.


What happens in the mechanical process of turning large chunks of plastic into small bits of plastic that will more readily dissolve in oil is far different than what happens under heat and pressure in the chemical soup of motor oil in a operating engine.

I will happily read any references that you can point me to that show viscosity improvers don't oxidize and are not part of sludge formation.

Ed

 

[4WD]

And would they degrade the same way ? Like say would a styrene type break down into smaller particles - or would the co-polymer type be susceptible to molecular rupture?

 

[SonofJoe]

Originally Posted By: edhackett
Originally Posted By: SonofJoe

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.


What happens in the mechanical process of turning large chunks of plastic into small bits of plastic that will more readily dissolve in oil is far different than what happens under heat and pressure in the chemical soup of motor oil in a operating engine.

I will happily read any references that you can point me to that show viscosity improvers don't oxidize and are not part of sludge formation.

Ed



Actually the process of solublising solid VII rubber or, shearing it down from say 50 SSI to 20 SSI is, if anything, a lot more severe than what you see in an engine. I can't remember the specific process conditions but you grind up rubber at relatively high applied pressures (solid OCP rubber is tough stuff so you have to apply a lot of oomph to chop it up) and you circulate it with base oil which starts off at 130°C but rises in temperature across the grinder because of all that mechanical energy you're putting in. The main difference between the grinder and oil/VII in an engine is of course time and the presence of oxygen (everything is nitrogen blanketed) but still, I don't think I ever saw any evidence of degradation.

I can't point you towards papers that say sheared VII doesn't contribute to oxidation and sludge. TBH, in all the time I was formulating, I don't think I ever read a single paper (a) because there was never enough time and (b) because the answers you're looking for as a formulator, are so specific, you have to figure out stuff for yourself. However if you look at industry standard tests like the Sequence IIIF, IIIG & VG, and you compare the performance of a marginal DI system with Group I to the equivalent Group II system (which to all intents and purposes contain the same amount of VII and will be subjected to the same levels of shear), then the results will be night an day; the Group I system will degrade while the Group II one won't. If sheared VII was playing such an active role, you might except this to show up in the Group II system but you don't. Such stuff is proprietary information and I no longer have access to it (so no sharing!) but I can assure I did do the work and that's what I saw.