Another "Taxi" Study: Relationship of Engine Bearing Wear and Oil Rheology 872128

[edhackett]

There were no details regarding the methodology of how the UOA were performed in the study.

Another sloppy SAE paper. A proper scientific paper will provide you with all of the information necessary to reproduce the experiment. In this case full details of the analytical method aren't required. The information necessary to retrieve the methodology can be conveyed in a single sentence.

"The oil samples were analyzed for wear metals on a [Make][Model] ICP following ABC method XYZ."
"The oil samples were analyzed for wear metals by ABC Laboratories [City], [State].*"
*Footnote or appendix entry giving full lab contact information or Lab's SOP referenced in the bibliography.

I see kschachn(thank you) has posted some of my past writings on why the typical UOA using ICP for wear metal analysis is not a proxy for wear. Ali, or anyone else that would like to ask further questions on the topic please do so. I'll follow this thread.

Ed

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[ZeeOSix]

Plain bearings are said to "self-pump" to some extent as long as there's an oil supply. (FB University)
Prime the system and it's good to go theory begat variable oil pumps.

They still benifit from more oil flow forced through them by the PD pump than they can naturally pump. Gives some flow headroom and helps to add bearing cooling from oil flow. Plus pump flow headroom ensures the bearings the farthest distance from the pump get adequate flow. The last thing any engine needs is an inadequately sized pump and/or oiling system to cover the entire spectrum of engine operation.

 

[OVERKILL]

Nothing was mentioned about the viscosity of the oil at drain time.
Back in the day, the evaporation rate vs shear down rate was a tool to keep the oil in grade.
Now of course with Noak limits, not so much.

edit; The loaded rod bearing at low rpm is the top or rod end, at high rpm, it's the cap bearing that's highly loaded as the piston goes over tdc.

Edit #2 as to the above post by Bill _W; Reducing geometric distortions in the engine case and crank should allow for reduced bearing clearances. Yes or no?

Yes, though I'm not sure if in practice it actually led to reduced bearing clearances in production applications, but I recall with Ford, this was one of the reasons the Modular was safe on xW-20 (from xW-30), the much more rigid lower block section and multi-bolt (including side bolt) main caps.

 

[OVERKILL]

Like "an extra layer of protection" (Havoline sales on a thicker motorcycle oil) and "headroom" drives bitoger' crazy.

Could then, is lower viscosity grades of engine oil begotten to a modern engine design that is "stiff" in your word.
A little play on words like which came first, the chicken or the egg?

Count the begats. Did engine design give birth to 0W16 or was it the other way around?

My understanding is that the pursuit of the thin oils happened first, and then engine design modifications were discovered to be necessary to make it work properly. This played out in Japan by their OEM's long before other marques were pursuing it.

 

[TiGeo]

They say that a manual transmission is an anti-theft device for millennials.

Like kiosk ordering at McDonalds or self checkout at the grocery store is Boomer Kryptonite.

My understanding is that the pursuit of the thin oils happened first, and then engine design modifications were discovered to be necessary to make it work properly. This played out in Japan by their OEM's long before other marques were pursuing it.

So in a nutshell for my caveman/geologist self.....if you run the oil that the OE recommends (w/r to "thin" oils), there is a high chance the engine was designed to handle said oil through bearing design etc. Correct?

 

[OVERKILL]

Like kiosk ordering at McDonalds or self checkout at the grocery store is Boomer Kryptonite.

So in a nutshell for my caveman/geologist self.....if you run the oil that the OE recommends (w/r to "thin" oils), there is a high chance the engine was designed to handle said oil through bearing design etc. Correct?

Yes, particularly with anything spec'ing 0W-16 and below due to it being determined that once you got much below the HTHS for an xW-20, that's where issues cropped up.

On the other hand, if you look at how many engines that clearly weren't designed around an xW-20 but were back-spec'd for it and it deemed safe, you can see that this "optimization" wasn't happening to the same degree. Bearing dimension and selection could be the same for two engines of the same family with one spec'ing 5W-20, the other 5W-50, one spec'ing 0W-20, the other 0W-40...etc, based on intended usage profile and "worst case scenario" conditions.

 

[TiGeo]

Yes, particularly with anything spec'ing 0W-16 and below due to it being determined that once you got much below the HTHS for an xW-20, that's where issues cropped up.

On the other hand, if you look at how many engines that clearly weren't designed around an xW-20 but were back-spec'd for it and it deemed safe, you can see that this "optimization" wasn't happening to the same degree. Bearing dimension and selection could be the same for two engines of the same family with one spec'ing 5W-20, the other 5W-50, one spec'ing 0W-20, the other 0W-40...etc, based on intended usage profile and "worst case scenario" conditions.

I also see that in the end, the science/math/engineering shows any way you slice it, the super thin oils like 0W16 and below have HTHS that is low enough that higher wear vs. a thicker 30/40W oil is fact, not speculation?

 

[wpod]

We leave out a few tidbits the pistons at TDC and BTC stop [dwell] rods break on the intake stroke at high RPMs and bend at high loads.
The electronic controls , Knock sensors and fuel injection greatly reduce the pounding on the crank and rod bearings from knocking type events and fuel "lean"mixure loads.
Why did Ford go back to 30 Wt + in its potential higher load engines?

 

[OVERKILL]

I also see that in the end, the science/math/engineering shows any way you slice it, the super thin oils like 0W16 and below have HTHS that is low enough that higher wear vs. a thicker 30/40W oil is fact, not speculation?

Yes, and this is the science of "mitigation" per the Honda study. Wider bearings, surface coatings...etc, all these things were utilized in their testing to reduce wear to "acceptable" levels. You are obviously aware of the Stribeck curve:

The shift to these thinner oils means more regions shift from hydrodynamic into mixed (and boundary), because, as @Shannow posted here:

Shifting Stribeck Curve to the Left: What to Use?

I've been trying to figure out what is out there that can boost the ability of an oil to form a tougher elastic oil film, i.e, super-lubricity (SL) to shift the Stribeck Curve to the left. Requirements: Any additive doing this must be synergistic, NOT surface-competitive, with ZDDP at the...

bobistheoilguy.com

An oil with lots of FM can ultimately get the best fuel economy in this region.

 

[OVERKILL]

We leave out a few tidbits the pistons at TDC and BTC stop [dwell] rods break on the intake stroke at high RPMs and bend at high loads.
The electronic controls , Knock sensors and fuel injection greatly reduce the pounding on the crank and rod bearings from knocking type events and fuel "lean"mixure loads.
Why did Ford go back to 30 Wt + in its potential higher load engines?

I assume a combination of the effects of fuel dilution and operating conditions resulting in unacceptable wear on the thinner oil.

 

[demarpaint]

Simple solution to this debate is for the "thin" lube proponents to run 0W5 or 0W8 in a vehicle which calls for 5W20 or 5W30, etc for 50K miles at 5K OCIs, and tear the engine down, if it lasts that long. That will put this debate to rest for good. Any takers?

 

[userfriendly]

We leave out a few tidbits the pistons at TDC and BTC stop [dwell] rods break on the intake stroke at high RPMs and bend at high loads.
The electronic controls , Knock sensors and fuel injection greatly reduce the pounding on the crank and rod bearings from knocking type events and fuel "lean"mixure loads.
Why did Ford go back to 30 Wt + in its potential higher load engines?

You sound like a lover of engine geometry. Why would a connecting rod break on the intake stroke? Would it be above the wrist pin? I can see the rod's cap end bearing being loaded as the piston is being pulled down against the partial vacuum in the cylinder. Higher compression ratios, heavier pistons, shorter connecting rods and a later intake valve opening point would all increase the downward load on the rod at all rpm's. Yes, no, or maybe?

 

[DGXR]

^ The greatest forces on the connecting rod are during piston acceleration which are not equal during all 4 strokes, due to the angles of the connecting rod between TDC vs BDC and vice-versa. The cylinder pressures during the compression and power strokes do affect the rod (piston acceleration forces) more than exhaust and intake strokes, but not much. More importantly, the designs of the big and small rod ends consider all these dynamic forces. In other words, the rod does not require the exact same amount of force to fail during compression vs during stretching forces.
Regarding the OP, engine oils and oiling systems have come a long way since the 1987 GM 4.3 V6. I would hope that more recent studies have been conducted.

 

[ZeeOSix]

I also see that in the end, the science/math/engineering shows any way you slice it, the super thin oils like 0W16 and below have HTHS that is low enough that higher wear vs. a thicker 30/40W oil is fact, not speculation?

Last time I checked ... Tribology science, engineering and testing to validate wasn't considered "speculation".

 

[Bill_W]

Last time I checked ... Tribology science, engineering and testing to validate wasn't considered "speculation".

However the advancement of car engineering go hand in hand with the advancement of lubricant engineering. Science is not stagment but always progressing. Do not stick around “old” science too long cause the “new” science is here and changing now.

 

[ZeeOSix]

Yes, though I'm not sure if in practice it actually led to reduced bearing clearances in production applications, but I recall with Ford, this was one of the reasons the Modular was safe on xW-20 (from xW-30), the much more rigid lower block section and multi-bolt (including side bolt) main caps.

Here's a shot of the Ford 5.0L Coyote main bearing caps. 4 bolts with 2 cross bolts. Factory service manual says the main bearing clearance is 0.0010 - 0.0018" and the rod bearing clearance is 0.0011 - .00027". The stock bottom end and rods can take ~800 HP reliably.

As you and others have pointed out many times, this engine is specified to run anything from 5W-20 to 5W-50 depending on use conditions.

 

[ZeeOSix]

However the advancement of car engineering go hand in hand with the advancement of lubricant engineering. Science is not stagment but always progressing.

Of course, never said is wasn't. Stop "bickering" ...

 

[kschachn]

However the advancement of car engineering go hand in hand with the advancement of lubricant engineering. Science is not stagment but always progressing. Do not stick around “old” science too long cause the “new” science is here and changing now.

The laws of physics haven’t changed no matter how badly someone might wish they have.

 

[Bill_W]

Of course, never said is wasn't. Stop "bickering" ...

The laws of physics haven’t changed no matter how badly someone might wish they have.

Engineering better engines and lubrication will always get more efficient. I am curious about the future advancements coming around the corner.

 

[ZeeOSix]

Engineering better engines and lubrication will always get more efficient. I am curious about the future advancements coming around the corner.

You're seeing it ... engines designed to run on 0W-16 and 0W-8. What's next? ... designed to run on 0W-0, lol.