Confessions of a Recovering Thickie

[siriusc1024]

Take a peek at the accompanying graphs from the paper you cite:
View attachment 280621

The steady-state advantage of the 0w20 at 25°C is on the order of 0.01 in friction coefficient.

At 100C, the steady state advantage is markedly less, perhaps 0.005.

Now consider the cyclic start-stop curves. The first start advantage of the 0w40 is about 0.01. In subsequent starts, their data suggests an advantage for the thinner oil of up to a whopping 0.0025.


This is the context for my commentary as follows:

• To the extent it's real (again, not actual engine testing), the advantage of the thinner oil is:
  • tiny at best
  • not present at initial start when it matters most
  • present *only* when combined with this DLC-like coating
  • Noteworthy ONLY because of the known fact of the converse. In other words, this is the exception that proves the rule. And what rule is that? The thicker oil provides better wear protection in most cases. If it wasn't for that "rule" nobody would care about this novel coating test data as an exception to it.

Why would you present your argument that way? No need to distort the data. In terms of percent, friction is reduced 8%-25%. Just because it's a decimal number doesn't mean tiny.

The only compelling argument here is that the data is valid only for the coating. Yes. I said that. I also said this is one of the things to be aware of when considering going against factory recommendations.

 

[siriusc1024]

I would love an explanation of why nobody runs 20w-50 continuously for the utmost best protection. Try to rationalize the thicker is better argument if you can.

 

[ZeeOSix]

Take a peek at the accompanying graphs from the paper you cite:

The steady-state advantage of the 0w20 at 25°C is on the order of 0.01 in friction coefficient.

At 100C, the steady state advantage is markedly less, perhaps 0.005.

I wonder how much of that difference is friction is due to the oil film shearing factor vs the actual surface asperities rubbing factor. They don't show the wear data, but obviously with special coatings on parts the wear should be lower because those coatings are designed to help mitigate wear when the film thickness gets super thin or goes to zero - ie, those coatings are more robust than the AF/AW tribofilm you get from just the oil. I'd read the whole study paper, but would have to pay for it to get the full download.

 

[ripcord]

I would love an explanation of why nobody runs 20w-50 continuously for the utmost best protection. Try to rationalize the thicker is better argument if you can.

Because thick enough is thick enough. The argument is over how much safety margin is enough for certain conditions.

 

[ZeeOSix]

I would love an explanation of why nobody runs 20w-50 continuously for the utmost best protection. Try to rationalize the thicker is better argument if you can.

First off, 20W shouldn't be used unless the ambient start-up temps allow that "W" grade to be used. As mentioned a few times in this thread, the Ford GT500, Boss 302 and Mustang Coyote with the Track Pack all specify 5W-50 for all use conditions. Any variant of that engine (even the ones that specify 5W-20) could also run 5W-50 all day long if someone wanted to use it for whatever reason ... like going to the track every weekend and not wanting to change oil back and forth every week. Some Mustang guys do run 5W-50 all the time, even though it was speced for 5W-20. And all the variants of that engine have the same journal bearing clearance specs. Engines are not "sensitive" to thicker KV100 oil grades, or "require" thinner oils, as seen in OMs for the same engines used in different countries without EPA/CAFE regulations. Engines however can be sensitive to the "W" rating for obvious reasons.

 

[tolian21]

If its API approved engine oil, you can run it, even if it ends with 50.

 

[Strumpan_]

C20, C30, A40...those euro specs you love. They have explicitly defined viscosity ranges.

What if it is Dexos oil? Will it be better than anything ever?

 

[ZeeOSix]

Why would you present your argument that way? No need to distort the data. In terms of percent, friction is reduced 8%-25%. Just because it's a decimal number doesn't mean tiny.

The only compelling argument here is that the data is valid only for the coating. Yes. I said that. I also said this is one of the things to be aware of when considering going against factory recommendations.

Contact friction is obviously going to be lower in boundary and mixed lubrication when there's a special coating involved - piston skirts have been coated for a long time. Special coatings mitigate wear better than just the AF/AW tribofilm layer from the oil (ie, the film strength of the oil) when the film thickness gets too low or goes to zero. That is one of the tricks used in engines able to run 0W-8 and 0W-16. Those two viscosities are only specified for engines with special design features - including wider journal bearings. That's why they have their own spec designation and unique API logo on the bottle. They don't want people using those viscosities in engines not designed for them. But that doesn't mean you could go up a grade or two ... and some people have done that. MIght even be an OM or two in another country posted somewhere for those engnes with a range of viscosity. Those special coatings will still work as intended even with a thicker oil, regardless of that that study is thought to say.

 

[siriusc1024]

Because thick enough is thick enough. The argument is over how much safety margin is enough for certain conditions.

That's right. I don't disagree that thicker oil provides better protection, but I also understand that too thick is going to cause problems. In fact, when I select oil I look up the PDS and factor in the viscosity at 100C. I also prefer the thicker oil. However, I do this within the confines of the spec.

Oil grades are not a spec, they are a recommendation. Plus the fact that in recent times they aren't based on anything but what the manufacturer is required to do based on EPA testing. In other words, politics. What is recommended in the manual is the lowest HT/HS that can be used to prevent excessive wear and nothing else. It is not necessarily optimal for longevity. It is acceptable under most circumstances to prevent excessive wear. That's it.

This right here exemplifies one of the problems I see a lot. Many times someone asks for an oil recommendation, and the recommendations are something way out of spec. Pretty much all the specifications define a viscosity range. Some have a minimum viscosity. All the specs factor in viscosity. Go ahead and look it up.

Thicker is better is sloppy. You'll see things like people recommending 502 where 508 is called for, arguments for 5w-30 in a car specd 0w-16, and let's not forget about the guys who swear by Rotella T4 15w-40 in their 5w-30 cars.

Thicker is better is correct in terms of protection, but it stops being correct when deviating from spec. When something like 0w-20 is required as opposed to recommended there's a difference. I gave one reason why this is. I can give more, but I don't think it'll be received well by people who have their minds made up.

It's not accurate to globally say thicker is better. It's important to consider the spec and application.

 

[siriusc1024]

What if it is Dexos oil? Will it be better than anything ever?

Dexos1 gen 3 is 0w-20 or 5w-30.
https://www.gmdexos.com/brands/dexos1_3/index.html

 

[ripcord]

That's right. I don't disagree that thicker oil provides better protection. In fact, when I select oil I look up the PDS and factor in the viscosity at 100C. I also prefer the thicker oil. However, I do this within the confines of the spec.


This right here exemplifies one of the problems I see a lot. Many times someone asks for an oil recommendation, and the recommendations are something way out of spec. Pretty much all the specifications define a viscosity range. Some have a minimum viscosity. All the specs factor in viscosity. Go ahead and look it up.

Thicker is better is sloppy. You'll see things like people recommending 502 where 508 is called for, arguments for 5w-30 in a car specd 0w-16, and let's not forget about the guys who swear by Rotella T4 15w-40 in their 5w-30 cars.

Thicker is better is correct in terms of protection, but it stops being correct when deviating from spec. When something like 0w-20 is required as opposed to recommended there's a difference. I gave one reason why this is. I can give more, but I don't think it'll be received well by people who have their minds made up.

It's not accurate to globally say thicker is better. It's important to consider the spec and application.

The thing is, "the spec" is not created in a vacuum. Things other than pure engineering considerations DO come into play. The spec is a series of tradeoffs and various considerations which inescapably includes CAFE.

 

[siriusc1024]

The thing is, "the spec" is not created in a vacuum. Things other than pure engineering considerations DO come into play. The spec is a series of tradeoffs and various considerations which inescapably includes CAFE.

There are tradeoffs and various considerations from an engineering standpoint as well. Too high viscosity makes bearings run hotter. It can also fail to ingress in sufficient quantity to non-pressurized locations. Don't neglect the importance of oil volume and cooling.

 

[tcp71]

The next thing they will ask why not put 75w-90 transfer oil

If it has the right chemisty, it matches right up to a 15w50 engine oil.

 

[ripcord]

There are tradeoffs and various considerations from an engineering standpoint as well. Too high viscosity make bearings run hotter. It can also fail to ingress in sufficient quantity to non-pressurized locations. Don't neglect the importance of oil volume and cooling.

There's a hundred plus years of experience to show that the historically used thicker weights of oil do not cause too high of bearing temps. Thicker may even be better in that regard because oil comes up to operating temps more quickly. Cold oil is way worse in terms of wear prevention, and as we know most engine wear happens during warm up.

 

[ZeeOSix]

Dexos1 gen 3 is 0w-20 or 5w-30.
https://www.gmdexos.com/brands/dexos1_3/index.html

Need to step up to dexos R to get the xW-40 and xW-50 grades.

 

[siriusc1024]

Need to step up to dexos R to get the xW-40 and xW-50 grades.

Yep. Viscosity is in the spec.

 

[ZeeOSix]

Yep. Viscosity is in the spec.

More like each dexos spec covers a range of viscosities.

 

[siriusc1024]

More like each dexos spec covers a range of viscosities.

Yes. So stay within the range.

There's also the disclaimer.

"GM dexos R engine oils meet or exceed the performance of GM dexos 2 and GM dexos 1 Gen 2 and Gen 3 oils and are backward compatible, therefore vehicles equipped with gasoline engines that used GM dexos 2, or GM dexos 1 Gen 2 or Gen 3 may use a GM dexos R licensed engine oil of the appropriate viscosity grade at their next oil change.
https://www.gmdexos.com/brands/dexosr/index.html

 

[Glenda W.]

Need to step up to dexos R to get the xW-40 and xW-50 grades.

AKA euro oil. Right back where we started.

 

[ZeeOSix]

If it has the right chemisty, it matches right up to a 15w50 engine oil.

Yep, most people don't know that 75W-90 gear oil isn't any higher in KV100 viscosity than 15W-50.