Are thinner oils about fuel economy or tighter engines?

[ArthurArgentum]

Always thought it was only about fuel economy but with better manufacturing techniques and wanting better performance squeezed out of engines could it involve tighter tolerances as well?

Your thoughts?

Well, thoughts of mine then

When it comes to lubricants viscosity, there are several important aspects of engines to consider. As mentioned before here, one of the main challenges lies in refining surface roughness and reducing bearings clearance.
Over time, clearances have generally decreased, with German engines holding no particular disadvantage over American or Japanese motors in this regard (Why they need more viscosity?? Please abstain from expounding upon temperature, for the question served but a rhetorical purpose.)
Now, let's explore the significance of viscosity reduction and its impact on engine oils.
By using oils with lower viscosity, we can achieve a few benefits. Firstly, the oil flows down more easily, which is a small but positive advantage. Secondly, and more importantly, lower viscosity oils have greater solvent capacity.

In modern engines, issues like oil coking and piston ring sticking have become common. These problems can be attributed to various factors, including the quality and viscosity of the oil. While the amount of polymer & additives in the oil plays a role, it's not the most critical aspect. It's possible to produce SAE40 oil with a small amount of polymer, but for certain applications like PCMO in winter, mineral 600 base oil without polymer is not suitable.

So, Law: when we decrease viscosity, we enhance the solvent capacity of the oil due to the physico-chemical properties of liquids. I am comming to realize that there is no need to embark upon a daunting search for identical oil series, meticulously comparing their D611 and D1133 characteristics, It suffices to say that reducing viscosity leads to increased dissolving capabilities. But I guided by the profound wisdom encapsulated within two fundamental equations: [Stokes - Einstein] and [Nernst - Brunner]. Should you desire, I am more than willing to share the some insights of these revered equations.

Boosters like esters can be used, but they also tend to provide better results in SAE16 oils compared to SAE40 oils. However, it's important to note that even boosters have limitations. Esters have limitations in PCMOs a lot.
In essence, within a chosen series of oils with similar compositions, lower viscosity oils always exhibit superior dissolving capabilities.
An "average" SAE16 oil can have solvent capacities up to 1.5 times better than a chemically similar "average" SAE40 oil. Moreover, the starting temperature for dissolving forces and optimal dispersibility is much lower for SAE16 oil, often at around 85°C, while SAE40 oil requires temperatures of 115°C or higher.
In conclusion, reducing viscosity can significantly improve engine cleanliness and the performance of piston rings - both crucial factors in modern internal combustion engines.
Now, we must come to terms with a singular truth: contemporary low-viscosity oils are crafted from remarkably tenacious and non-volatile synthetic bases, rendering them impervious to the volatility that plagued thin oils of yesteryears.

 

[Al]

It has been my line of study for the last 55 years or so.
The topic here was reasons for thinner oils. I just listed one item of concern.
And how thicker lube will not flow so great through a fine mesh screen.

I am truly sorry that after 55 years of "study" you came up with this conclusion.

Also-subaru's FA engine can either be NA ore Turbo. The turbo requires 30 wt the NA uses 20 wt. oil.

Doesn't that say it all?

 

[ZeeOSix]

When it comes to lubricants viscosity, there are several important aspects of engines to consider. As mentioned before here, one of the main challenges lies in refining surface roughness and reducing bearings clearance.
Over time, clearances have generally decreased, with German engines holding no particular disadvantage over American or Japanese motors in this regard (Why they need more viscosity?? Please abstain from expounding upon temperature, for the question served but a rhetorical purpose.)

As mentioned many times in these type of discussions, the clearances between moving parts in engines has been virtually the same for decades. Parts clearances can only go so low before they start over heating and destroying themselves, regardless of the oil viscosity between them. On thing that most people don't consider is the smaller the clearance, the higher the shear rate in the bearing, and therefore a larger oil temperature rise inside the bearing which in turn makes the oil even thinner inside the bearing. At some point, a smaller clearance can lead to a fast cascading failure due to over heating the bearing and MOFT going to zero. Too tight bearing clearance will smoke a bearing way faster than a too loose bearing clearance.

With all factors held constant, thicker oil always results in more MOFT between moving parts, even in tight bearings. Oil film thickness due to viscosity (HTHS is key) is the main factor that keeps parts from rubbing and wearing. Film strength (the AF/AW add pack) is what helps mitigate wear when the MOFT goes to zero and parts start rubbing together. As oils have become thinner, the AF/AW add packs have become more robust.

Oil temperature certainly is a key factor in all of this, because oil temperature effects the viscosity, which effects the MOFT. That is why OMs that call out a range of specified oil viscosity show what viscosity to use vs the ambient temperature use range of the vehicle. Obviously, oil coolers play a role in keeping oil temps down, which makes using thinner oil less risky. CAFE has driven the move to thinner and thinner oils, and also the need for more robust film strength add packs.

A good example that shows that engine parts made as tight as possible don't really care about the oil viscosity are motorcycle engines that rev to 11,000+ RPM using 20W-50 oils. This is also seen in OMs for the same car engines used in different countries that don't abide by CAFE and show a whole range of specified oil viscosity in the OMs. The minimum service manual specs for my XSR900 shows clearances as low as follows, yet Yamaha specs oil viscosity all the way up to 20W-50:

Rod Big End: 0.001 in
Crankshaft: 0.0006 in
Camshaft: 0.001 in
Piston to Cylinder: 0.0004 in
Piston Pin: 0.0003 in

Thicker oil gives more MOFT in looser bearings than thinner oil, but thicker oil also gives more MOFT
even in tighter bearings.

 

[ArthurArgentum]

With all factors held constant, thicker oil always results in more MOFT between moving parts, even in tight bearings. Oil film thickness due to viscosity (HTHS is key) is the main factor that keeps parts from rubbing and wearing. Film strength (the AF/AW add pack) is what helps mitigate wear when the MOFT goes to zero and parts start rubbing together. As oils have become thinner, the AF/AW add packs have become more robust.

Oil temperature certainly is a key factor in all of this, because oil temperature effects the viscosity, which effects the MOFT. That is why OMs that call out a range of specified oil viscosity show what viscosity to use vs the ambient temperature use range of the vehicle. Obviously, oil coolers play a role in keeping oil temps down, which makes using thinner oil less risky. CAFE has driven the move to thinner and thinner oils, and also the need for more robust film strength add packs.

My focus thus far has been centered solely on elucidating the benefits derived from viscosity reduction. I have succinctly outlined two key advantages in this regard.
However, when considering the pursuit of heightened viscosity for enhanced protection, a nuanced perspective emerges. In the realm of hydrodynamic lubrication theory, the emphasis lies not on excessive viscosity, but rather on attaining a viscosity that is sufficient.
It is important to note that a more viscous oil primarily leads to increased pumping losses and reducing the flow rate (flow down). Consequently, visible advantages of thickening are scarce when the oil already possesses adequate viscosity.
Yet, determining the threshold of adequacy proves to be a challenging task. Some scholars suggest an PCMO HTHS (not all 4T engines!) viscosity of 2 cP, while others propose even lower values. Ultimately, the optimal viscosity depends on the roughness of the bearings and the clearances in question. Thus, no further discernible advantages can be attributed beyond these considerations.

mentioned work -

 

[ZeeOSix]

My focus thus far has been centered solely on elucidating the benefits derived from viscosity reduction. I have succinctly outlined two key advantages in this regard.
However, when considering the pursuit of heightened viscosity for enhanced protection, a nuanced perspective emerges. In the realm of hydrodynamic lubrication theory, the emphasis lies not on excessive viscosity, but rather on attaining a viscosity that is sufficient.
It is important to note that a more viscous oil primarily leads to increased pumping losses and reducing the flow rate (flow down). Consequently, visible advantages of thickening are scarce when the oil already possesses adequate viscosity.
Yet, determining the threshold of adequacy proves to be a challenging task. Some scholars suggest an PCMO HTHS (not all 4T engines!) viscosity of 2 cP, while others propose even lower values. Ultimately, the optimal viscosity depends on the roughness of the bearings and the clearances in question. Thus, no further discernible advantages can be attributed beyond these considerations.

mentioned work -

Just as I said ... the lower the viscosity, the lower the MOFT and the decrease in engine protection. And in reality, that was a short term test, so extrapolate that out to 200K miles and an engine running that thin of oil that long isn't going to wear well if it's not specifically designed for such a thin oil, like the engines specifying 0W-8 and 0W-16 these days. You can go on YT and find videos of engines running and being beat to death with WD-40 in the sump, but they will eventually destroy themselves.

Yes, it's a "balance", and a matter of how much wear protection headroom someone wants for their engine. Many here like more MOFT headroom, and it's not something that is detrimental in any way to the engine operation. All it does is possibly costing a thin hair of fuel mileage - the main focus of CAFE and why oils have become thinner and thinner. There is no other reason than that, because thinner oil does not and never will provide more wear protection than a thinner oil with all other factors being constant. It's a basic law of Tribology that will never change.

 

[ArthurArgentum]

There is no other reason than that, because thinner oil does not and never will provide more wear protection than a thinner oil with all other factors being constant. It's a basic law of Tribology that will never change.

Should your beliefs lean solely towards the conspiracies of environmentalists, then indeed, no reasons beyond that realm may sway your perception.
However, I have already presented tangible justifications, shedding light on the potential benefits derived from viscosity reduction. I have referenced specific equations and highlighted the significance of factors like flow rate / improved cooling / solubility.
The threshold of PCMO viscosity sufficiency remains subjective, with debates between SAE30 or SAE30 ILSAC proponents and those who find SAE20 quite suitable. However, it is important to acknowledge the influence of extreme summer conditions, especially in Egypt, Mexico, Arizona

 

[ZeeOSix]

Should your beliefs lean solely towards the conspiracies of environmentalists, then indeed, no reasons beyond that realm may sway your perception.

The laws of Tribology and mechanical physics of machinery sway my perception more than anything. If environmentalists and CAFE never existed, the drive for ever decreasing oil viscosity adventures wouldn't be like it has/is. Obviously, some people want more fuel mileage, even if it means a bit less wear protection for the engine.

However, I have already presented tangible justifications, shedding light on the potential benefits derived from viscosity reduction. I have referenced specific equations and highlighted the significance of factors like flow rate / improved cooling / solubility.
The threshold of PCMO viscosity sufficiency remains subjective, with debates between SAE30 or SAE30 ILSAC proponents and those who find SAE20 quite suitable. However, it is important to acknowledge the influence of extreme summer conditions, especially in Egypt, Mexico, Arizona

There really are no tangible benefits from using a thinner KV100 or HTHS viscosity oil besides a potential increase in fuel economy at the risk of less engine protection headroom and possible increased wear. However, there certainly is a benefit from using the correct "W" rated oil for the minimum expected cold start-up conditions.

What "equations" have you shown to support your claims? Many studies show the relationship between HTHS viscosity and engine wear, and not one study shows that reducing the HTHS viscosity below a certain point results in less wear or no increase in wear. The lower the HTHS viscosity becomes, the less wear protection there is. Most people that understand Tribology don't like running on the ragged edge of MOFT.

BTW, the "flow rate" of the oil to the areas supplied under pressure by the PD is a non-issue if you know how a PD pump and oiling system works. There's a good reason PD oil pumps are used on engines - to ensure an adequate oil volume flow regardless of viscosity. As said earlier, bearings and other engine components are as tight as they can get, regardless of the oil viscosity used. If those tight clearances were a big factor, then you would not see any engine specify a wide range of oil viscosity like some OMs (not CAFE driven) show. And why do you think the specified oil viscosity is higher in those hotter climates like Egypt, Mexico, Australia, etc?

 

[ArthurArgentum]

What "equations" have you shown to support your claims? Many studies show the relationship between HTHS viscosity and engine wear, and not one study shows that reducing the HTHS viscosity below a certain point results in less wear or no increase in wear. The lower the HTHS viscosity becomes, the less wear protection there is. Most people that understand Tribology don't like running on the ragged edge of MOFT.

I did not intend to reference wear, nor did I mention it in my previous communication -
In modern engines, issues like oil coking and piston ring sticking have become common. These problems can be attributed to various factors, including the quality and viscosity of the oil. While the amount of polymer & additives in the oil plays a role, it's not the most critical aspect. It's possible to produce SAE40 oil with a small amount of polymer, but for certain applications like PCMO in winter, mineral 600 base oil without polymer is not suitable.

So, Law: when we decrease viscosity, we enhance the solvent capacity of the oil due to the physico-chemical properties of liquids. I am comming to realize that there is no need to embark upon a daunting search for identical oil series, meticulously comparing their D611 and D1133 characteristics, It suffices to say that reducing viscosity leads to increased dissolving capabilities. But I guided by the profound wisdom encapsulated within two fundamental equations: [Stokes - Einstein] and [Nernst - Brunner]. Should you desire, I am more than willing to share the some insights of these revered equations.

BTW, the "flow rate" of the oil to the areas supplied under pressure by the PD is a non-issue if you know how a PD pump and oiling system works. There's a good reason PD oil pumps are used on engines - to ensure an adequate oil volume flow regardless of viscosity.

Y'see, deep inside that engine, there's a whole lot of oil. Once it's done runnin' through them channels and gaps, it starts to drain down 'cause of gravity. And let me tell ya, that thin oil picks up better speed as it goes. Does that make things clearer for ya?

 

[kschachn]

I did not intend to reference wear, nor did I mention it in my previous communication -
In modern engines, issues like oil coking and piston ring sticking have become common. These problems can be attributed to various factors, including the quality and viscosity of the oil. While the amount of polymer & additives in the oil plays a role, it's not the most critical aspect. It's possible to produce SAE40 oil with a small amount of polymer, but for certain applications like PCMO in winter, mineral 600 base oil without polymer is not suitable.

So, Law: when we decrease viscosity, we enhance the solvent capacity of the oil due to the physico-chemical properties of liquids. I am comming to realize that there is no need to embark upon a daunting search for identical oil series, meticulously comparing their D611 and D1133 characteristics, It suffices to say that reducing viscosity leads to increased dissolving capabilities. But I guided by the profound wisdom encapsulated within two fundamental equations: [Stokes - Einstein] and [Nernst - Brunner]. Should you desire, I am more than willing to share the some insights of these revered equations.



Y'see, deep inside that engine, there's a whole lot of oil. Once it's done runnin' through them channels and gaps, it starts to drain down 'cause of gravity. And let me tell ya, that thin oil picks up better speed as it goes. Does that make things clearer for ya?

I think that’s a bunch of bull.

But maybe that’s just me.

 

[eroberts82]

Tighter tolerances in manufacturing, but not tighter clearances with regard to engine specs.

.0005 is .0005 in the past, and it will be in the future............

 

[ZeeOSix]

I did not intend to reference wear, nor did I mention it in my previous communication -

Keeping wear down is a key purpose of any lubricant. Most big name oils on the self today do a real good job of keeping rings free and engines clean as long as the OCI is kept to a reasonable length. That's the last thing I'm concerned about, and more focused on keeping the wear down, which keeps the engine healthy and as close to new as possible.

Y'see, deep inside that engine, there's a whole lot of oil. Once it's done runnin' through them channels and gaps, it starts to drain down 'cause of gravity. And let me tell ya, that thin oil picks up better speed as it goes. Does that make things clearer for ya?

LoL ... do you really think the difference of how hot xW-8 vs xW-60 drains back to the sump really matters? It doesn't. And if the correct "W" rating is used, then the drain down to the sump in a cold start-up/warm-up will basically be the same and not matter in the real world. You think the sump is going to go "dry" in any of those circumstances? Maybe if someone made a bonehead move and revved the engine to redline when the oil is below zero ... then the sump might go "dry" and starve the pump inlet and blow-up the engine, but whoever does a move like that deserves a blown-up engine.

 

[MolaKule]

I did not intend to reference wear, nor did I mention it in my previous communication -
In modern engines, issues like oil coking and piston ring sticking have become common. These problems can be attributed to various factors, including the quality and viscosity of the oil. While the amount of polymer & additives in the oil plays a role, it's not the most critical aspect. It's possible to produce SAE40 oil with a small amount of polymer, but for certain applications like PCMO in winter, mineral 600 base oil without polymer is not suitable.

So, Law: when we decrease viscosity, we enhance the solvent capacity of the oil due to the physico-chemical properties of liquids. I am comming to realize that there is no need to embark upon a daunting search for identical oil series, meticulously comparing their D611 and D1133 characteristics, It suffices to say that reducing viscosity leads to increased dissolving capabilities. But I guided by the profound wisdom encapsulated within two fundamental equations: [Stokes - Einstein] and [Nernst - Brunner]. Should you desire, I am more than willing to share the some insights of these revered equations.
Does that make things clearer for ya?

So you're telling me that my 3.4 cSt Chevron PAO's have more solvency than my 8 cSt Hatcol PO esters?

Did you by chance major in Thesaurus Studies?

 

[ArthurArgentum]

So you're telling me that my 3.4 cSt Chevron PAO's have more solvency than my 8 cSt Hatcol PO esters?

Did you by chance major in Thesaurus Studies?

Regrettably, I am unable to make such a statement. Furthermore, upon revisiting my previous message, it becomes apparent that I good highlighted the role of esters as solubility boosters.
However, it is important to be aware that an excessive quantity of such boosters, such as a ratio of 40% esters to 60% other SHC, may potentially lead to complications.
As also I mentioned earlier, lower viscosity esters tend to exhibit improved solubility characteristics regardless. Therefore, the act of employing solvency boosters in SAE16 oils yields superior results compared to the process of boostering SAE40 oils, regardless of the circumstances.

 

[ArthurArgentum]

LoL ... do you really think the difference of how hot xW-8 vs xW-60 drains back to the sump really matters? It doesn't. And if the correct "W" rating is used, then the drain down to the sump in a cold start-up/warm-up will basically be the same and not matter in the real world. You think the sump is going to go "dry" in any of those circumstances?

I must clarify that none of the points you mentioned in your response align with my intended message. My original statement emphasized the minor advantage associated with low viscosity, specifically its capacity for enhanced fluid movement and the resulting benefits. I stressed this particular aspect, highlighting the advantages derived from its faster drainage capabilities.
I did not imply any concerns about the sump becoming dry or the sluggish drainage of viscous oil. Instead, I specifically discussed the swifter movement of low-viscosity oil, which undoubtedly enhances fluid flow at certain points.
I kindly request that you exercise greater care in comprehending the precise contents of my written communication.

 

[ZeeOSix]

I must clarify that none of the points you mentioned in your response align with my intended message. My original statement emphasized the minor advantage associated with low viscosity, specifically its capacity for enhanced fluid movement and the resulting benefits. I stressed this particular aspect, highlighting the advantages derived from its faster drainage capabilities.
I did not imply any concerns about the sump becoming dry or the sluggish drainage of viscous oil. Instead, I specifically discussed the swifter movement of low-viscosity oil, which undoubtedly enhances fluid flow at certain points.

Explain just how the oil draining down to the sump a hair faster is beneficial in any way when the sump level will never get even close to below the oil pump pick-up, especially when the oil is hot. What do you think the difference in drain down time is between a 0W-8 and a 20W-50 is when the oil is at 200F - ?. It's not even a concern when the oil is super cold and 1000 times thicker in a very cold start-up as long as the correct "W" rating is used. If it was a concern, there would be blown-up engines all over the country during the cold winter months because the thick oil didn't drain back to the sump fast enough, and the oil pump started sucking air and starved the engine of proper oil flow. When is the last time you saw that happen unless someone redlined the engine right after a very cold start-up Doing something stupid like that might cause the pump to suck air and cause engine damage.

What about cold start-ups ... the oil is 100s of times more viscous, yet engines survive just fine as long as the correct "W" rating is used. If they are not damaged in that case, then they certainly are not damaged from oil flow down driven by gravity when the oil is 200F. I think you're looking for some kind of red herring with this oil drain back by gravity focus.

I kindly request that you exercise greater care in comprehending the precise contents of my written communication.

I highly request that you exercise greater care in explaining your claims, which seem to be all over the place.

 

[ArthurArgentum]

Keeping wear down is a key purpose of any lubricant. Most big name oils on the self today do a real good job of keeping rings free and engines clean as long as the OCI is kept to a reasonable length. That's the last thing I'm concerned about, and more focused on keeping the wear down, which keeps the engine healthy and as close to new as possible.

To which specific type of mechanical wear are you referring? Are you addressing the wear experienced by the bearing pads? In most cases, such wear cannot be attributed to viscosity alone but rather indicates a potential malfunction in the pump or insufficient oil supply. Is there a particular engine component that is particularly susceptible to wear caused by viscosity? Could it be the camshaft, perchance? It is important to note that viscosity alone cannot effectively address or mitigate any form of wear. In reality, instances of wear resulting directly from viscosity are quite rare. However, approximately 50% occurrences of oil burning due to sticking piston rings have been observed. This is where the true challenges lie. Placing excessive emphasis on viscosity appears to only exacerbate the existing problem
.

 

[ZeeOSix]

To which specific type of mechanical wear are you referring? Are you addressing the wear experienced by the bearing pads? In most cases, such wear cannot be attributed to viscosity alone but rather indicates a potential malfunction in the pump or insufficient oil supply. Is there a particular engine component that is particularly susceptible to wear caused by viscosity? Could it be the camshaft, perchance? It is important to note that viscosity alone cannot effectively address or mitigate any form of wear. In reality, instances of wear resulting directly from viscosity are quite rare. However, approximately 50 occurrences of oil burning due to sticking piston rings have been observed. This is where the true challenges lie. Placing excessive emphasis on viscosity appears to only exacerbate the existing problem

Seems you should do some self-research on engine wear in both terms of viscosity, and the oil cleanliness factor too while you're at it. Lots of things beside inadequate lubrication (ie, a lack of) can cause increased engine wear. Stuck rings, carbon and sludge build-up are not caused because of the oil viscosity used.

 

[ArthurArgentum]

Explain just how the oil draining down to the sump a hair faster

First and foremost, it is essential to recognize that the flow rate of oil layers directly impacts heat transfer. In confined spaces, this enhanced flow significantly improves heat transfer by promoting greater mobility of the oil layers. The significance of oil layer mobility in overcoming limitations in heat transfer has been extensively discussed in numerous scholarly papers dedicated to this subject. Dismissing this as a trivial matter would be unwise. Fully comprehending it requires a firm grasp of heat balance calculations, a thorough understanding of the "heat equation," and proficiency in solving Cauchy's conditions associated with it.

 

[ZeeOSix]

First and foremost, it is essential to recognize that the flow rate of oil layers directly impacts heat transfer. In confined spaces, this enhanced flow significantly improves heat transfer by promoting greater mobility of the oil layers. The significance of oil layer mobility in overcoming limitations in heat transfer has been extensively discussed in numerous scholarly papers dedicated to this subject. Dismissing this as a trivial matter would be unwise. Fully comprehending it requires a firm grasp of heat balance calculations, a thorough understanding of the "heat equation," and proficiency in solving Cauchy's conditions associated with it.

If that was such a big concern then why do all high performance car makers specify thicker oil for race track use of the car? The temperature rise inside the journal bearing with thicker oil is small and not one bit of a concern. The advantage of the thicker oil to provide more MOFT and more engine protection significantly outwighs the delta in oil temperature rise. If thinner oil was better at protecting engines, then they would specify thinner oil for race track use ... but they instead specify thicker oil.

Show me some of those equations and corresponding test data showing what the temperature rise difference is with all factors held constant except for the oil viscosity.

 

[ArthurArgentum]

Stuck rings, carbon and sludge build-up are not caused because of the oil viscosity used.

I shall refrain from repeating, once again, that concepts such as dispersions, dissolution work, or detergents exhibit improvements with a decrease in viscosity (considering the same chemical components in comparative formulations). Moreover, in practical terms, the production of oils predominantly relies on base oils with KV100 viscosities of 4 and 6, often referred to as "average synthetics". Whether we examine SAE40 or SAE20 oils, the majority are formulated using base oils with average kinematic viscosities at 100°C of 4 and 6. However, it is noteworthy that SAE20 oil requires thickening to attain a viscosity of 8, whereas SAE40 necessitates thickening to achieve a viscosity of 14. This thickening process can be accomplished (average blending maker or formulation) by incorporating polymer thickeners (it further reduces solvent capacity). Additionally, it is essential to acknowledge the supplementary "synthetic" requirement of utilizing purer (group III, IV) oils with reduced dissolving power to safeguard the stability of the CCS.