In thick vs thin don't forget the additives

[Solarent]

All this thick vs thin debate continuing over the past several days I thought it would be good to review one of the fundamental principles of lubrication relating to selecting the right viscosity. Here is some information about the Stribeck Curve taken from the STLE website:
Originally Posted By: STLE
Stribeck Curve
The Stribeck Curve is a plot of the friction as it relates to viscosity, speed and load. On the vertical axis is the friction coefficient. The horizontal axis shows a parameter that combines the other variables: mN/P. In this formula, m is the fluid viscosity, N is the relative speed of the surfaces, and P is the load on the interface per unit bearing width. Basically, as you move to the right on the horizontal axis, the effects of increased speed, increased viscosity or reduced load are seen. The zero point on the horizontal axis corresponds to static friction.

The combination of low speed, low viscosity and high load will produce boundary lubrication. Boundary lubrication is characterized by little fluid in the interface and large surface contact. We can see on the Stribeck curve that this results in very high friction.

As the speed and viscosity increase, or the load decreases, the surfaces will begin to separate, and a fluid film begins to form. The film is still very thin, but acts to support more and more of the load. Mixed lubrication is the result, and is easily seen on the Stribeck curve as a sharp drop in friction coefficient. The drop in friction is a result of decreasing surface contact and more fluid lubrication. The surfaces will continue to separate as the speed or viscosity increase until there is a full fluid film and no surface contact. The friction coefficient will reach its minimum and there is a transition to hydrodynamic lubrication. At this point, the load on the interface is entirely supported by the fluid film. There is low friction and no wear in hydrodynamic lubrication since there is a full fluid film and no solid-solid contact.

You might notice that the Stribeck curve shows the friction increasing in the hydrodynamic region. This is due to fluid drag (friction produced by the fluid) - higher speed may result in thicker fluid film, but it also increases the fluid drag on the moving surfaces. For example, think about how much harder it is to run in a pool of water than it is to walk. Likewise, a higher viscosity will increase the fluid film thickness, but it will also increase the drag. Again, think about the difference between walking in air and walking in a pool of water.

Machinery will see boundary lubrication at start-up and shutdown (low speeds and thin film), before transition to hydrodynamic lubrication at normal operating conditions (high speeds and thick film). Inspection of the Stribeck curve will show us that a machine will see the most friction and wear during start-up and shutdown.

Note: The Stribeck curve above is plotted in log-log format, so each tick represents a 10X increase over the previous interval.


Choosing the right viscosity for your engine means choosing the one where the combination of SAE grade, engine speed and load meet at the bottom of the curve. This is going to be different for everyone as the conditions will be different. However, general recommendations are made for the average person by engine manufacturers.

In today's oils, great progress is being made on both sides of the bottom of the curve (representing the optimal viscosity) to reduce friction in these areas. On the boundary side (or left of the base of the curve) chemical additives such as friction modifiers, antiwear additives and ep components of engine oils which provide protection when viscosity alone is not enough. On the hydrodynamic side (or the right of the base of the curve) more stable viscosity properties of high index, lower viscosity base oils are reducing frictional drag. Today's oils are the sum of their parts not just one attribute or one component of the base or additive package. (Good base oils + High performing additives = Great Oil)

The principles of the stribeck curve can also be applied to fuel economy improvement as a reduction in friction also produces real fuel economy benefits for engine designs which are paired with these newer oils.

 

[SteveSRT8]

Thank you for a nicely posted series of facts.

 

[Oil Changer]

Great read. Thank you.

 

[SrDriver]

Good job!

Thanks for posting.

 

[Nate1979]

What percent of the people who post in the thick vs thin debate actually understand the math and science enough to make an educated recommendation? My background is not in this area so I know that I don't.

I'm guessing it is pretty low unless the classes offered in automotive engineering school includes the following classes:
Feelings 101 - covers how running different oils makes you feel good or bad
Engine sounds and oil 201 - covers how to tell if your engine is louder or softer on specific lubricant and how that makes your car feel
Interpretive used oil analysis 301 - covers how to use a cheap $20 used oil analysis to extrapolate internal engine wear so you never have to tear down an engine again

And lastly, Thesis topic - how to use the Euro oil manufacturers website to choose the proper oil for your engine because your future classmates (sitting next to you) won't know how to do it properly when they write those stupid owners manuals.

 

[Donald]

Thanks for posting.

But don't the car manufacturers know all of this when they come up with a recommended viscosity for a vehicle? Thus purchase quality oil that meets what is in the owners manual?

I am sure I could read up on how a Tetanus vaccine works with my body's antibodies. And it might be interesting. But can one read up on everything that might be interesting? In the case of the Tetanus vaccine, I can ask my doc a question or two, but basically trust him to provide me a proper vaccine.

 

[Solarent]

Originally Posted By: Donald
But don't the car manufacturers know all of this when they come up with a recommended viscosity for a vehicle? Thus purchase quality oil that meets what is in the owners manual?


Yes they do make their recommendations based on these principles and a host of other factors. But there is no one size fits all response when it comes to oil choice. Every application is different and will have a different "optimal". That is why oils are designed with a wide range of protections in the additive package and the viscosity performance.

My advice has always been use the manufacturer recommendation as a basis for a starting point and if you operate outside the box they recommend then adjust accordingly. Tools used for condition monitoring can provide insights to your specific application if you choose to make it important to you. If it's not that important, and you don't want to think about it, follow the OEM recommendation and change your oil regularly. Ultimately the decision is yours.

 

[friendly_jacek]

I don't think we are forgetting the additives while talking modern oils. If no additives were used, we would all have to use 20W50 oils to stay away from boundary friction wiping out valve train while increasing the friction in pistons/liners due to high viscosity (right part of the curve).

The additives allow using thinner modern oils to manage boundary friction protecting the valve train while decreasing the friction in pistons due to low viscosity (keeping them at the bottom part of the curve).

So, what we need to remember, different parts of internal combustion engine work under different friction regimes.

 

[Pop_Rivit]

Originally Posted By: Nate1979
I'm guessing it is pretty low unless the classes offered in automotive engineering school includes the following classes:
Feelings 101 - covers how running different oils makes you feel good or bad
Engine sounds and oil 201 - covers how to tell if your engine is louder or softer on specific lubricant and how that makes your car feel
Interpretive used oil analysis 301 - covers how to use a cheap $20 used oil analysis to extrapolate internal engine wear so you never have to tear down an engine again



You failed to mention this one:

Fuel Mileage 101 - Increasing your fuel mileage 24% with this one weird oil change trick. And the instructor for this class? Gas stations HATE him!

 

[Solarent]

Originally Posted By: friendly_jacek
The additives allow using thinner modern oils to manage boundary friction protecting the valve train while decreasing the friction in pistons due to low viscosity (keeping them at the bottom part of the curve).

So, what we need to remember, different parts of internal combustion engine work under different friction regimes.


Agreed 100%.

 

[jrustles]

Originally Posted By: Solarent

But there is no one size fits all response when it comes to oil choice. Every application is different and will have a different "optimal".


Key point here. And as mentioned in the past few days, bearing design is changing to accommodate hydrodynamic lubrication using the thinner oils, but not drastically.

The example stribeck plot should also be clarified. To the left, we have the friction occurring via boundary lubrication-- where the part is literally down to the molecular layer of metallic protective additives. To the far right, the subject part is well separated; the friction cost being simply between the oil molecules itself, grabbing onto each other and friction surfaces, resisting being torn apart.

I still assert that the move to thinner oils is mostly driven by fuel economy mandates. It's very difficult to make a case that it's driven by improving wear protection. CAFE isn't from a fairy tale, it's very real mandate and currently is not the only one automakers are facing internationally.

OTOH
From a metal-to-metal wear protection perspective, it's far more prudent IMO, to err to the right of the curve. A 150ish VI 'ancient' 10w30 is still not a fantastic, outrageous, way-out-of-spec jump from a 150ish VI 5w20- just with a more reliable hthSv.


Also notable in the furnished stribeck example, is that the lube regime quickly enters full hydrodynamic from mixed in short order (~5x increase in potential film thickness), whereas 'excessive' friction from the higher-than-required bearing viscosity@given bearing speed doesn't even come close to the pre-hydrodynamic point, even at over '100 times increase' in potential fluid film thickness, or bearign speed or whatever the x axis represents

.

The 0W20/30/40 are different animals, and usually require more robust bases/PI packs to begin with, so generalizations about these grades are difficult to make, as their composition can vary WILDLY from blender to blender, spec-to-spec.

Originally Posted By: friendly_jacek


The additives allow using thinner modern oils to manage boundary friction protecting the valve train while decreasing the friction in pistons due to low viscosity (keeping them at the bottom part of the curve).

So, what we need to remember, different parts of internal combustion engine work under different friction regimes.

 

[turtlevette]

Originally Posted By: jrustles
Originally Posted By: Solarent

But there is no one size fits all response when it comes to oil choice. Every application is different and will have a different "optimal".


Key point here. And as mentioned in the past few days, bearing design is changing to accommodate hydrodynamic lubrication using the thinner oils, but not drastically.

The example stribeck plot should also be clarified. To the left, we have the friction occurring via boundary lubrication-- where the part is literally down to the molecular layer of metallic protective additives. To the far right, the subject part is well separated; the friction cost being simply between the oil molecules itself, grabbing onto each other and friction surfaces, resisting being torn apart.

I still assert that the move to thinner oils is mostly driven by fuel economy mandates. It's very difficult to make a case that it's driven by improving wear protection. CAFE isn't from a fairy tale, it's very real mandate and currently is not the only one automakers are facing internationally.

OTOH
From a metal-to-metal wear protection perspective, it's far more prudent IMO, to err to the right of the curve. A 150ish VI 'ancient' 10w30 is still not a fantastic, outrageous, way-out-of-spec jump from a 150ish VI 5w20- just with a more reliable hthSv.


Also notable in the furnished stribeck example, is that the lube regime quickly enters full hydrodynamic from mixed in short order (~5x increase in potential film thickness), whereas 'excessive' friction from the higher-than-required bearing viscosity@given bearing speed doesn't even come close to the pre-hydrodynamic point, even at over '100 times increase' in potential fluid film thickness, or bearign speed or whatever the x axis represents

.

The 0W20/30/40 are different animals, and usually require more robust bases/PI packs to begin with, so generalizations about these grades are difficult to make, as their composition can vary WILDLY from blender to blender, spec-to-spec.

Originally Posted By: friendly_jacek


The additives allow using thinner modern oils to manage boundary friction protecting the valve train while decreasing the friction in pistons due to low viscosity (keeping them at the bottom part of the curve).

So, what we need to remember, different parts of internal combustion engine work under different friction regimes.

The stuff Solara quoted is how lubrication works in a bearing. The cam and rings have different considerations and modes of lubrication.

Your long winded "discussions" would have more credibility if you recognized that as oil gets too thick there are lubrication issues. Not just CAFE considerations.

You're putting yourself in the grumpy old man category. The government is ruining your life and your engine. Your kind didn't want air bags in cars because it was going to make them too expensive. You didn't want to take lead out of gas. You don't want ethanol because it's going to destroy everything. You don't want the thin oil because it's going to ruin your engine. Ford and other manufs tell you 0W-20 works best. The other thread had quite an extensive Q&A from Ford. But no one can tell you any different.

The irony is most of the cars thick oils are going into barely get the oil hot enough to flash off the water.

Why choose an oil that will be at optimal viscosity at 280 deg which is really almost never going to happen? As much as people think they are speed racers, they really aren't. You have to drive a while at flat out to get to these temps. You just can't do it here. I would make an argument you can't do it on the autobahn anymore either. Its getting too congested.

 

[demarpaint]

Originally Posted By: Solarent
But there is no one size fits all response when it comes to oil choice.

I see I'm in good company.

 

[turtlevette]

Originally Posted By: jrustles
Key point here. And as mentioned in the past few days, bearing design is changing to accommodate hydrodynamic lubrication using the thinner oils, but not drastically.



From what I'm reading it is pretty drastic. Going from a trimetal design with lead, zinc and copper to a silicon impregnated aluminum.

Now I wonder if we will have updated replacements for old stuff like my frist gen small block chevy.

 

[jrustles]

Originally Posted By: turtlevette
The stuff Solara quoted is how lubrication works in a bearing. The cam and rings have different considerations and modes of lubrication.

Your long winded "discussions" would have more credibility if you recognized that as oil gets too thick there are lubrication issues. Not just CAFE considerations.





Such as pumpability issues raised in my last thread?
You're more than welcome to elaborate on your vacuous abstractions of course, as bolded above.


Also, do you work on a farm? Because you seem to have an endless supply of hay to build all these strawmen, when clearly listed, explicit points of concern would be more useful.

 

[jrustles]

Originally Posted By: turtlevette
Originally Posted By: jrustles
Key point here. And as mentioned in the past few days, bearing design is changing to accommodate hydrodynamic lubrication using the thinner oils, but not drastically.



From what I'm reading it is pretty drastic. Going from a trimetal design with lead, zinc and copper to a silicon impregnated aluminum.

Now I wonder if we will have updated replacements for old stuff like my frist gen small block chevy.


How familiar are you with automotive engines? Well enough to know that tri-metal bearings are decades old? Well, if not, now you know. Next?

 

[Clevy]

Ole turt and his not even close wisdom again.
My hemi will run oil temps of 210 or so once it stabilizes on the highway. If I out my foot into it and hold the gears til 5500 rpm I can get the oil temp up to 280 in a couple if minutes. So so much for that winning theory.
And as far the the grumpy old man goes turt you take the cake. Your wrong 95% of the time and are so focused on proving your incorrectness is correct you completely miss and ignore the obvious.
I thank god that my mind is open enough to learn and admit when I'm wrong. You aren't there yet,and likely never will be,which is why not a single person here gives anything you write a second thought,unless they feel like embarrassing you.
I kinda feel sorry for you,but you do it to yourself.

 

[jrustles]

'As the saying goes, it takes all kinds to make the world go around, though perhaps some shouldn't go quite so far around it as others.'

 

[A_Harman]

Originally Posted By: jrustles
Originally Posted By: turtlevette
Originally Posted By: jrustles
Key point here. And as mentioned in the past few days, bearing design is changing to accommodate hydrodynamic lubrication using the thinner oils, but not drastically.



From what I'm reading it is pretty drastic. Going from a trimetal design with lead, zinc and copper to a silicon impregnated aluminum.

Now I wonder if we will have updated replacements for old stuff like my frist gen small block chevy.


How familiar are you with automotive engines? Well enough to know that tri-metal bearings are decades old? Well, if not, now you know. Next?


He's not even right about the "alternative" bearing material. Bimetal aluminum bearings have also been around for decades, only they're aluminum-tin alloys, not aluminum-silicon.

 

[A_Harman]

Originally Posted By: turtlevette
The stuff Solara quoted is how lubrication works in a bearing. The cam and rings have different considerations and modes of lubrication.



You're dead wrong at the outset, turtlevette. The Stribeck curve is a general description of lubrication between sliding surfaces, whether they are planar or curved.