Toyota's reasoning for 0w20 viscosity engine oil

[Gokhan]

Originally Posted By: fpracha
Originally Posted By: Gokhan
Regarding fuel economy, 0W-20 and 5W-20 have identical fuel-economy criteria under GF-5. So, you aren't guaranteed at all to see any fuel-economy improvement whatsoever over 5W-20. A tiny (around 0.1 MPG) improvement may result under certain conditions, assuming the 0W-20 and 5W-20 oils have very similar additive packages. A 5W-20 oil with a better friction-modifier package can easily beat a 0W-20 oil in fuel economy.

There is really no cold-start benefit either unless you live in extremely cold climates (Canada, Alaska, etc.), as the cold viscosity is not that different from 5W-20.

So is it also possible and true then that a super-high-quality 15w40 oil with "more effective friction modifiers" can have a very similar (or just slightly lower) fuel economy as the 5w20 or 0w20 ?

Absolutely no. Fuel economy (engine friction) is mainly determined by the HTHS viscosity. Friction modifiers are secondary.

The current SAE limit on HTHS viscosity is 2.6 cP to prevent possible engine damage due to oil-film breakdown. Auto manufacturers have been trying hard to have the limit lowered further to satisfy future government fuel-economy standards. Note that diesel engines require much larger HTHS viscosity because they generate a lot of torque at low RPM, where the oil film is thin. CJ-4 minimum is 3.5 cP.

0W-20 and 5W-20 both have 2.6 cP HTHS viscosity. On top of that, GF-5 spec on fuel economy is the same for both. The actual efficiency will be determined by the amount and quality of friction modifiers. Also, used synthetic oil may have more fuel efficiency than used dino oil, as the synthetic oil deteriorates more slowly.

If the same additive packages and friction modifiers are used, expect to see only about 0.1 MPG improvement for using 0W-20 instead of 5W-20, due to slightly lower cold viscosity.

 

[CATERHAM]

Originally Posted By: Gokhan
Originally Posted By: fpracha

0W-20 and 5W-20 both have 2.6 cP HTHS viscosity. If the same additive packages and friction modifiers are used, expect to see only about 0.1 MPG improvement for using 0W-20 instead of 5W-20, due to slightly lower cold viscosity.

You do love to generalize without giving specifics.
There are plenty of 0W-20 and 5W-20 oils with HTHS viscosities higher than 2.6cP such as all M1 oils, Amsoil, RL, RLI and PU to name just a handful.
Also you're claim of only 0.1 mpg for a 0W-20 over a 5W-20 couldn't be more misleading. The Toyota 0W-20 due in large part to it's ultra high 216 VI is a good 35% lighter even at room temperature than a typical 5W-20 and more than 50% at 32F. That alone will result is a good 4% fuel savings for a typical user and even more for short trippers that don't get the oil up to normal operating temp's a lot of the time.

 

[Gokhan]

Originally Posted By: CATERHAM
That alone will result is a good 4% fuel savings for a typical user and even more for short trippers that don't get the oil up to normal operating temp's a lot of the time.

Oh, come on now, CATERHAM. 4% fuel savings within same the SAE viscosity grade? EPA would have mandated everyone to use Toyota oil if that was the case.

Not to mention that all other car manufacturers would switch to Toyota oil by themselves to boost their fuel-economy claims.

 

[CATERHAM]

That percentage is from Toyota Canada specifically referring to operation in a Prius and having used the oil I believe it.

Mobil claims 2% for their AFE 0W-20 and 0W-30 oils and that's with no appreciable viscosity or VI difference to other oils of the same grade..

 

[Gokhan]

Originally Posted By: CATERHAM
That percentage is from Toyota Canada specifically referring to operation in a Prius and having used the oil I believe it.

Mobil claims 2% for their AFE 0W-20 and 0W-30 oils and that's with no appreciable viscosity or VI difference to other oils of the same grade..

One thing that is very important to realize is that the fuel economy (engine friction) of an oil is determined mostly by its HTHS viscosity, not by its SAE (kinematic) viscosity. SAE (kinematic) viscosity plays only a very small role in fuel economy.

For example a 5W-30 oil with an HTHS viscosity of 3.0 cP will have significantly (several percent) more fuel economy than the German Castrol 0W-30 with an HTHS viscosity of 3.5 cP.

Yes, you will see a small difference in fuel economy between 0W-20 and 5W-20 if their HTHS viscosities are the same and they use the same friction modifiers. But it will only be a small fraction of a percent -- almost impossible to measure for the driver.

Of course, you and I and everyone else on this board know not to take any marketing claim by any company seriously.

 

[45ACP]

Originally Posted By: CATERHAM
Originally Posted By: Gokhan
Originally Posted By: fpracha

0W-20 and 5W-20 both have 2.6 cP HTHS viscosity. If the same additive packages and friction modifiers are used, expect to see only about 0.1 MPG improvement for using 0W-20 instead of 5W-20, due to slightly lower cold viscosity.

You do love to generalize without giving specifics.
There are plenty of 0W-20 and 5W-20 oils with HTHS viscosities higher than 2.6cP such as all M1 oils, Amsoil, RL, RLI and PU to name just a handful.
Also you're claim of only 0.1 mpg for a 0W-20 over a 5W-20 couldn't be more misleading. The Toyota 0W-20 due in large part to it's ultra high 216 VI is a good 35% lighter even at room temperature than a typical 5W-20 and more than 50% at 32F. That alone will result is a good 4% fuel savings for a typical user and even more for short trippers that don't get the oil up to normal operating temp's a lot of the time.



Honda (Idemitsu) 0W-20is better with an even higher VI right?

You just made me want the highest VI oil, ever.

Fuel tackes a backseat to vroom vroom due to less engine resistance.

 

[Gokhan]

Originally Posted By: 45ACP
Honda (Idemitsu) 0W-20is better with an even higher VI right?

You just made me want the highest VI oil, ever.

Fuel tackes a backseat to vroom vroom due to less engine resistance.

Guys, please, you should learn this by now:

Engine friction is not determined by the kinematic viscosity or the kinematic-viscosity index. It's determined by the HTHS viscosity.

They should put this on the home page of Bob is the Oil Guy so that people stop making false statements about engine friction vs. kinematic viscosity.

 

[JOD]

Originally Posted By: Gokhan

Guys, please, you should learn this by now:

Engine friction is not determined by the kinematic viscosity or the kinematic-viscosity index. It's determined by the HTHS viscosity.

They should put this on the home page of Bob is the Oil Guy so that people stop making false statements about engine friction vs. kinematic viscosity.


Like most of your other generalizations, this isn't really true. hths is the primary driver once the oil is up to full operating temperature. Have you actually looked at the average trip length people take in their cars? There's a reason the EPA FE tests are conducted with a significant component of cold starts/incomplete warm-ups. For MOST of the driving people actually DO, kinematic viscosity IS a significant component when you're talking about fuel economy.

 

[Gokhan]

Originally Posted By: JOD
Originally Posted By: Gokhan

Guys, please, you should learn this by now:

Engine friction is not determined by the kinematic viscosity or the kinematic-viscosity index. It's determined by the HTHS viscosity.

They should put this on the home page of Bob is the Oil Guy so that people stop making false statements about engine friction vs. kinematic viscosity.


Like most of your other generalizations, this isn't really true. hths is the primary driver once the oil is up to full operating temperature. Have you actually looked at the average trip length people take in their cars? There's a reason the EPA FE tests are conducted with a significant component of cold starts/incomplete warm-ups. For MOST of the driving people actually DO, kinematic viscosity IS a significant component when you're talking about fuel economy.

You should really educate yourself on this. You don't know the difference between kinematic viscosity and high-shear viscosity and the different roles they play. Kinematic viscosity vs. high-shear viscosity has nothing to do with temperature.

For beginners:

* Kinematic viscosity determines only slow oil flow up and down trough the engine and and oil pumpability, not engine friction. Slow motion is the key here.
* High-shear viscosity is a dynamic viscosity that determines the friction forces between the fast moving (shearing) engine parts (as well as oil-film thickness between the fast moving parts). Fast motion is the key here.

What you're missing is that HTHS not only refers to high temperature but also "high shear." High shear is the key in understanding engine friction. Unlike the kinematic viscosity, HTHS viscosity is a dynamic viscosity.

Most people think that engine friction is caused by the oil being pumped through the engine. This would be given by the kinematic viscosity. This is not the case! Oil pumping is only a tiny fraction of the energy loss in an engine. Engine friction is mostly caused by the fast sliding parts temporarily shearing the oil. This is a different, dynamic viscosity then the kinematic viscosity, which is not a dynamic viscosity, and it even has different units (cP vs. cSt). It's called the high-shear viscosity. It could be measured at low temperatures -- low-temperature, high-shear viscosity (LTHS) -- or at high temperatures -- high-temperature, high-shear viscosity (HTHS). But in any case, it's the high-shear viscosity that determines the friction, not the kinematic viscosity. Kinematic viscosity mainly determines oil pumpability and flow. It's true that the high-shear viscosity is usually only specified for high temperature (150 C) but this is for practical reasons, as people are usually concerned with the engines operating at normal temperatures and don't want to complicate things.

Don't take my word on this alone, as there are so many references and research papers on this. Here are some:

A Chevron presentation (See especially the figure on Page 16)

The classic read on HTHS viscosity

In fact, CATERHAM himself as a nice write-up on this board.

Repeat:

Kinematic viscosity = oil pumbability and flow (more the KV viscosity, more the pressure but less the pumpability and flow)
High-shear viscosity = engine friction and fuel economy (more the HS viscosity, more the minimum oil-film thickness and more wear protection but also more the friction and less the fuel economy)

Moral of the story: KINEMATIC VISCOSITY AND HIGH-SHEAR VISCOSITY ARE DIFFERENT THINGS. DON'T CONFUSE OIL PUMPABILITY WITH ENGINE FRICTION. THERE IS USUALLY A CORRELATION BUT THERE IS NO DIRECT QUANTITATIVE CORRESPONDENCE. ENGINE FRICTION IS ULTIMATELY DETERMINED BY A DYNAMIC VISCOSITY CALLED THE HIGH-SHEAR VISCOSITY, NOT DIRECTLY BY THE KINEMATIC VISCOSITY.

 

[Garak]

Originally Posted By: CATERHAM
Additionally their are no "super-high quality 15W-40 oils". It's a dino grade and as others have mentioned the synthetic 5W-40 grade has replaced it.


Well, RP does market a synthetic 15w-40 HDEO. I can't name any others, though.

 

[Gokhan]

By the way, if you really wanted to determine the friction an oil causes in a cold engine, you would have to measure the LTHS (low-temperature, high-shear) viscosity for that oil. Engine oil is not a Newtonian fluid. There are a lot of polymers in it, which behave differently under high-shear conditions, in other words between fast-sliding parts. Think of honey for example. Its viscosity will be much different if you try to stir it fast. High-shear viscosity is measured at a rate of 1/1,000,000 seconds. Therefore, it's useful in determining friction caused by an oil between fast-sliding parts. On the other hand, kinematic viscosity is measured under very slow conditions. Therefore, it's useful mainly for quantifying oil pumping.

There is usually a correlation between kinematic viscosity and high-shear viscosity, but not a one-to-one correspondence. For example, Mobil 1 0W-30 and German Castrol 0W-30 have almost identical kinematic viscosities and viscosity indices. But the German Castrol 0W-30 has much larger HTHS viscosity (3.5 vs 3.0 cP) and therefore 3 - 4% less fuel economy and more engine friction. For the same reason, you can't directly judge an oil's cold-engine fuel economy from its cold kinematic viscosity or viscosity index alone. You would need the low-temperature, high-shear viscosity to actually figure out the cold-engine friction caused by an oil.

Your best bet for determining an oil's overall fuel economy is to know its HTHS viscosity. If, on top of that, there is a great friction-modifier package, you will have even more fuel economy. Kinematic viscosity and viscosity index alone will only give you a rough idea and you shouldn't try to quantify the kinematic viscosity and viscosity index into fuel economy.

 

[JOD]

Originally Posted By: Gokhan

You should really educate yourself on this. You don't know the difference between kinematic viscosity and high-shear viscosity and the different roles they play. Kinematic viscosity vs. high-shear viscosity has nothing to do with temperature.


I'd suggest re-reading what you wrote above, then re-consider who should be "educating himself"....

When you find an 0W20 oil with an hths of 3.5, let me know.

KV and hths are, indeed, related, and hths and KV are both directly related to temperature. "temperature" does happen to be the "t" in temperature...

 

[Gokhan]

One last thing to add to my discussion of the kinematic vs. high-shear viscosity:

Even when the temperature of the oil sump is very low, a lot of friction is generated between the sliding engine parts, which raises the temperature of the oil film between these parts, probably at least to around 100 C. Therefore, the best indicator of the friction between sliding parts is the high-temperature, high-shear viscosity (HTHS) viscosity -- even when the oil-sump temperature is below freezing. (Ignore my comments about the low-temperature, low-shear viscosity in my previous post, as a low-temperature, low-shear viscosity is not very useful for the reason I just mentioned here.)

Once again:

* Use the kinematic viscosity (cold or hot) mostly to determine cold cranking, oil pressure, and oil flow. It's not a good indicator of fuel economy.

* Use the HTHS viscosity to determine the fuel economy (engine friction) and the protection against engine wear (minimum oil-film thickness [MOFT]) Note that fuel economy and MOFT go against each other.

I hope all this has helped in clarifying some of the somewhat complicated concepts behind kinematic and apparent (dynamic) viscosity (HTHS viscosity) and how they relate to engine performance. For straight-grade oil, you don't have to worry about HTHS viscosity. But for multigrade oil, the polymer molecules (viscosity-index improvers) temporarily shear (loose viscosity) under high shear (fast sliding motion). This is the reason why you need the HTHS viscosity instead of kinematic viscosity to quantify fuel economy. It also needs to be of high temperature because the oil film between the fast sliding parts always has a high temperature.

HTHS viscosity is your best friend in determining fuel economy and protection against oil-film breakdown.

 

[JOD]

Originally Posted By: Gokhan


* Use the HTHS viscosity to determine the fuel economy (engine friction) and the protection against engine wear (minimum oil-film thickness [MOFT]) Note that fuel economy and MOFT go against each other.[/b]



Overwhelmingly, most people are picking oils with relatively fixed hths. For instance, if you're selecting a 0W20 or 5W20 oil because that's what your car requires, the majority of non-boutique oils with be between 2.6-2.7. If you're choosing between oils of similar/identical hths, the one which has lighter KV at start-up is going to increase FE--all else being equal. You seem instant on ignoring this part of the equation.

 

[Gokhan]

Originally Posted By: JOD
KV and hths are, indeed, related, and hths and KV are both directly related to temperature. "temperature" does happen to be the "t" in temperature...

See what I just posted. Friction is determined by the oil film between fast-sliding parts, and the temperature of this oil film will be high even when the oil sump is at a very low temperature. Since the sliding parts slide very fast (high shear) and the temperature is high due to the friction generated (high temperature), you need the high-temperature, high-shear (HTHS) viscosity to help quantify an oil's friction in an engine, not the kinematic viscosity.

In my posts above, the difference between the HTHS and kinematic viscosities are explained in detail. It's explained where and how they should be used and where not to be used. If low-temperature kinematic viscosity determined the engine friction, there would be so much friction in an engine in frigid temperatures that you wouldn't even be able to shift to the second gear.

 

[Gokhan]

Originally Posted By: JOD
Overwhelmingly, most people are picking oils with relatively fixed hths. For instance, if you're selecting a 0W20 or 5W20 oil because that's what your car requires, the majority of non-boutique oils with be between 2.6-2.7. If you're choosing between oils of similar/identical hths, the one which has lighter KV at start-up is going to increase FE--all else being equal. You seem instant on ignoring this part of the equation.

Again, please read my posts above. I'm hearing what you're saying and explaining it. If the HTHS viscosities are given the same, the difference between 0W- and 5W- is mainly cold-cranking ability and cold-oil pumpability and flow. It won't affect your fuel economy much. The fuel economy will still be determined mostly by the HTHS viscosity as I just explained in my last two posts above. It's mostly a marketing move, as well as a logistics simplification, by Toyota, Honda, etc. to claim that 0W-20 has noticeably better fuel economy than 5W-20. It has not.

 

[CATERHAM]

It's true that fuel economy correlates with HTHSV, all other factors being equal. That includes the CoF of the base oils, add' pac's and the oil's VI.

The Toyota 0W-20 has a 216 VI. A typical dino 5W-20 has a 150 VI. So even if the two oils have the same 2.6cP HTHSV their actual operational viscosities will be markedly different.
Even at 100C the Toyota oil will be almost 10% lighter and as I mentioned earlier more than 35% at room temperature and almost 60% lighter at 0C.
Considering the normal operating temperature for most engines is about 90C and that it can take up to 30 minutes to reach (if at all in the winter months), average oil operating temperature can be quite low. And this is where the advantage of the ultra high VI Toyota 0W-20 oil shines. It may technically be a 20wt oil but due to it's ultra high VI is effectively much lighter with the correspondingly higher fuel economy to show for it.

 

[Gokhan]

Originally Posted By: CATERHAM
It's true that fuel economy correlates with HTHSV, all other factors being equal. That includes the CoF of the base oils, add' pac's and the oil's VI.

The Toyota 0W-20 has a 216 VI. A typical dino 5W-20 has a 150 VI. So even if the two oils have the same 2.6cP HTHSV their actual operational viscosities will be markedly different.
Even at 100C the Toyota oil will be almost 10% lighter and as I mentioned earlier more than 35% at room temperature and almost 60% lighter at 0C.
Considering the normal operating temperature for most engines is about 90C and that it can take up to 30 minutes to reach (if at all in the winter months), average oil operating temperature can be quite low. And this is where the advantage of the ultra high VI Toyota 0W-20 oil shines. It may technically be a 20wt oil but due to it's ultra high VI is effectively much lighter with the correspondingly higher fuel economy to show for it.

But the point is that the temperature at the bearings and cylinder rings is always high, even when the oil sump is at a low temperature. That's because friction generates a lot of heat at these fast-sliding surfaces. The loss in horsepower and fuel economy is in terms of the heat generated by the friction at the bearings and cylinder rings, and this heat instantly raises the temperature there even when the oil sump is at a below-freezing temperature. Conversely, if no large quantities of heat were generated at the bearings and rings to instantly raise the temperature there, this would mean that there is no fuel-economy and horsepower loss, which doesn't make sense.

This is the reason why, when they talk about the high-shear viscosity -- the viscosity that applies to the oil friction in fast-sliding (fast-shearing) parts, they only talk about high-temperature, high-shear (HTHS) viscosity and never about low-temperature, high-shear viscosity because the temperature at the bearings and rings is always high, much higher than the oil-sump temperature, easily exceeding 150 C (standard temperature for measuring HTHS viscosity) even when the oil-sump temperature is 40 C or below.

 

[JOD]

Originally Posted By: Gokhan

But the point is that the temperature at the bearings and cylinder rings is always high, even when the oil sump is at a low temperature. That's because friction generates a lot of heat at these fast-sliding surfaces. The loss in horsepower and fuel economy is in terms of the heat generated by the friction at the bearings and cylinder rings, and this heat instantly raises the temperature there even when the oil sump is at a below-freezing temperature. Conversely, if no large quantities of heat were generated at the bearings and rings to instantly raise the temperature there, this would mean that there is no fuel-economy and horsepower loss, which doesn't make sense.

This is the reason why, when they talk about the high-shear viscosity -- the viscosity that applies to the oil friction in fast-sliding (fast-shearing) parts, they only talk about high-temperature, high-shear (HTHS) viscosity and never about low-temperature, high-shear viscosity because the temperature at the bearings and rings is always high, much higher than the oil-sump temperature, easily exceeding 150 C (standard temperature for measuring HTHS viscosity) even when the oil-sump temperature is 40 C or below.



To borrow a quote from you, "you should really educate yourself about this"...

Give this a start: PDF LINK

The paper points out pretty clearly some basic things which you insist on ignoring:

-the relationship between dynamic viscosity and KV (which you continue to claim doesn't exist)

-the actual source of losses in an ICE. Hint: it's not just the bearings.

Of particular note, observe how oils of IDENTICAL hths behave during the different stages of the Sequence VI-A tests. The results are pretty much unequivocal: oils with lighter KV and similar hths increase efficiency significantly until the oil is up to operating temperatures. As I said earlier, given the actual driving that most people do, KV at start-up temperature is a significant component of a lubricants impact on fuel economy.

 

[CATERHAM]

You are really obfuscating the issue.
No matter how you measure viscosity (HTHSV and kinematic viscosity are inextricably linked) it varies dramatically with temperature.

HTHSV is sometimes called "bearing viscosity" because it correlates so closely with oil pressure in an operating engine (unlike KV100). You're going to have very much lower OP (a less viscous oil) with the Toyota 0W-20 on start-up all the way to operating temperature. The lighter the oil, the less oil drag and the better the fuel economy. What could be simpler than that.