Confessions of a Recovering Thickie

[siriusc1024]

Yes and the range is the lowest they can go without causing unacceptable wear. That’s it.

As Overkill notes above, it’s about tolerating lower HT/HS to achieve a rather small decrease in fuel consumption.

I understand what you're saying.

What I can't figure out is where do you define the limit of HT/HS to the point where it does harm than good? To define that limit would require knowledge of the specific engine.

What I really can't believe is that, with all the information out there and obviously intelligent people on this forum, the sum of tribology boils down to thicker is better.

Approaching both would lead to a nuanced approach and a further understanding of oil. When people think they have it figured out they stop learning.

What I see is that 0w-20 being a quick way to meet EPA specs is an assumption. Sometimes that is the case, and you see it on transition engines. Automotive engineers have all kinds of ways to adjust architecture to increase fuel efficiency. It is most certainly possible that some of these design changes require thinner oil for optimal performance and long life. That shouldn't be rejected outright. Not being willing to explore that possibility for yourself isn't going to further your knowledge. You'll be stuck and self-limited.

 

[Hohn]

HTHS and all other viscosity values basically come down to a binary outcome— you either have enough viscosity (i.e. MOFT) or you don’t. You are either in (elasto)/hydrodynamic lubrication or you are mixed or boundary lubrication. You can draw a line on the stribeck curve right where the curve starts spiking upward as you go left and divide the curve neatly in half between “enough” and “not enough” film thickness.

There are many parts of the engine that are quite far to the right on the Stribeck and therefore require very little viscosity to keep happy. Main bearings, for example, are pretty easy to keep in full hydrodynamic because there are no reversals and clearance is usually quite tight.

Top ring reversals however are almost impossible to keep in full hydrodynamic lubrication because of the reversal and the high temperatures that tend to thin the oil film on the bore surface and the top ring land area.

Viscosity is always a compromise. Driven by the pressure to eke out tenths of MPG, pumping loss minimization has been paramount and so modern engines run thinner oils that require less work to pump. They also tend to run the tightest practical clearances to reduce the leakage rate with thinner oils. The tighter clearance thing is generally good, because tighter clearances increase the load capacity of a journal bearing.

Thicker is not always better, your hunch is correct. The root of the issue is that different concepts of “better” exists and what an OEM thinks is “better” for regulatory compliance and planned obsolescence is likely to differ from what the customer thinks is “better” if he wants to keep a car forever and minimize wear and degradation.

Like most things in life, viscosity is a tradeoff. Some engines and duty cycles will show incredibly low wear on fairly low viscosity oils. Going thicker in these engines does nothing to lower wear rates.

There might be other reasons to prefer a thicker viscosity that have nothing to do with viscosity per se. Perhaps you like the 20C higher flashpoint of the 10w30 instead of the 5w20 because you believe that indicates lower volatility and less tendency to form intake deposits on your GDI engine. That seems like a valid reason to choose thicker oil even if ti has no benefit to slower wear rates. Wear is, after all, only one form of degradation. Cleanliness is another—arguably more relevant—form of degradation.

 

[siriusc1024]

HTHS and all other viscosity values basically come down to a binary outcome— you either have enough viscosity (i.e. MOFT) or you don’t. You are either in (elasto)/hydrodynamic lubrication or you are mixed or boundary lubrication. You can draw a line on the stribeck curve right where the curve starts spiking upward as you go left and divide the curve neatly in half between “enough” and “not enough” film thickness.

There are many parts of the engine that are quite far to the right on the Stribeck and therefore require very little viscosity to keep happy. Main bearings, for example, are pretty easy to keep in full hydrodynamic because there are no reversals and clearance is usually quite tight.

Top ring reversals however are almost impossible to keep in full hydrodynamic lubrication because of the reversal and the high temperatures that tend to thin the oil film on the bore surface and the top ring land area.

Viscosity is always a compromise. Driven by the pressure to eke out tenths of MPG, pumping loss minimization has been paramount and so modern engines run thinner oils that require less work to pump. They also tend to run the tightest practical clearances to reduce the leakage rate with thinner oils. The tighter clearance thing is generally good, because tighter clearances increase the load capacity of a journal bearing.

Thicker is not always better, your hunch is correct. The root of the issue is that different concepts of “better” exists and what an OEM thinks is “better” for regulatory compliance and planned obsolescence is likely to differ from what the customer thinks is “better” if he wants to keep a car forever and minimize wear and degradation.

Like most things in life, viscosity is a tradeoff. Some engines and duty cycles will show incredibly low wear on fairly low viscosity oils. Going thicker in these engines does nothing to lower wear rates.

There might be other reasons to prefer a thicker viscosity that have nothing to do with viscosity per se. Perhaps you like the 20C higher flashpoint of the 10w30 instead of the 5w20 because you believe that indicates lower volatility and less tendency to form intake deposits on your GDI engine. That seems like a valid reason to choose thicker oil even if ti has no benefit to slower wear rates. Wear is, after all, only one form of degradation. Cleanliness is another—arguably more relevant—form of degradation.

It can cause damage. One of the tricks I was talking about as far as architecture and fuel efficiency is ta-C coating on the rings. Thicker oil can degrade the coating and lead to accelerated wear.

"Current emphasis on automotive engine has evoked the desire to improve tribological performance by both reducing friction and making starting easier in the automotive industry. The present study was conducted to determine the effects of viscosity of fully-formulated oil on tribological properties of the typical coatings for automotive engine components, e.g. ta-C, CrN and Cr-diamond coatings, under simulated lubrication conditions. Results showed that compared to Cr-diamond and CrN coating, the ta-C coating exhibited superior tribological properties with the lowest friction coefficients and wear rates under various testing conditions. Low-viscosity oil 0W-20 could significantly improve the tribological properties of ta-C coatings at different testing temperatures. Furthermore, in cyclic start/stop tests, ta-C coatings have been proven to possess excellent low temperature cycle starting performance when lubricated by low-viscosity oil. A synergistic effect of the low-viscosity oil and a nanoscale adaptive tribofilm was speculated for ta-C coatings to be responsible for achieving lower friction and wear simultaneously. The lubrication adaptability of low-viscosity oil to ta-C coating is technologically important and provides a high potential of industrial application for lubrication and wear prevention under actual conditions."

https://www.sciencedirect.com/science/article/abs/pii/S0925963520307810

See what I mean about design changes aimed at improved efficiency can necessitate thinner oil?

The idea of taking something that makes sense, but applying it in a way that overrides what's already been experimentally verified, isn't the correct approach.

 

[ZeeOSix]

That said, my gut feeling is it'd probably be fine to step up from 0w20 to 5w30 in a high mileage car that was made after 2007. However that's just my best guess since I've never owned a car newer than 2007.

It would be totally fine to put xW-30 in any car specifying xW-20. Lot of people do it, and some even put up to xW-30 if a xW-16 is specified. Engines are not sensitive to KV100 grade, only sensitive to the wrong "W" grade.

 

[siriusc1024]

It would be totally fine to put xW-30 in any car specifying xW-20. Lot of people do it, and some even put up to xW-30 if a xW-16 is specified. Engines are not sensitive to KV100 grade, only sensitive to the wrong "W" grade.

I just showed that they can be.

 

[siriusc1024]

And another way is throwing off the calculations for oil delivery.

 

[ZeeOSix]

What I can't figure out is where do you define the limit of HT/HS to the point where it does harm than good? To define that limit would require knowledge of the specific engine.

Lots of high performance engines are recommended to use xW-50, Ford even says just use it all the time in engines like the GT500 because they know the user might beat the engine hard at times and so they also don't have to go change oil if they are going to track the car. Those engines have the same journal bearing clearances as the Coyote that can run down to 5W-20 on the streets. Bet you could put a xW-60 in those engines and it's not going to "do any harm". Some BMWs spec a xW-60 grade, and their bearings have the standard clearances. Technical info says that journal bearings obtain more MOFT with increased viscosity - there have been dozens if not 100s of threads discussing bearing MOFT vs viscosity and bearing clearances. The bad thing to do is try to run thinner oil in bearings with more clearance, but bearings with normal clearances don't mind thicker oil.

 

[siriusc1024]

And let's not forget about viscosity and turbo protection. Notice how it's in relation to temp? That's only valid for the viscosity specified.

 

[siriusc1024]

Lots of high performance engines are recommended to use xW-50, Ford even says just use it all the time in engines like the GT500 because they know the user might beat the engine hard at times and so they also don't have to go change oil if they are going to track the car. Those engines have the same journal bearing clearances as the Coyote that can run down to 5W-20 on the streets. Bet you could put a xW-60 in those engines and it's not going to "do any harm". Some BMWs spec a xW-60 grade, and their bearings have the standard clearances. Technical info says that journal bearings obtain more MOFT with increased viscosity - there have been dozens if not 100s of threads discussing bearing MOFT vs viscosity and bearing clearances. The bad thing to do is try to run thinner oil in bearings with more clearance, but bearings with normal clearances don't mind thicker oil.

If that's Ford's recommendation then they've done the work to make it valid haven't they? It's not some forum user making a claim that thicker is better. What's best is what's specified. Ford doesn't say xw-50 for all their engines.

MOFT also has to do with surface finish, journal size, and oil pressure. If MOFT is sufficient then why go up a grade or two? What's the tradeoff elsewhere?

 

[ZeeOSix]

HTHS and all other viscosity values basically come down to a binary outcome— you either have enough viscosity (i.e. MOFT) or you don’t.

And nobody has a real time MOFT monitor on every moving part inside the engine. Having a bit more MOFT by going up a grade from a xW-20 or less gives more film thickness, and therefore more parts separation and added wear protection. Nothing wrong with adding more wear protection from thicker oil.

There are many parts of the engine that are quite far to the right on the Stribeck and therefore require very little viscosity to keep happy. Main bearings, for example, are pretty easy to keep in full hydrodynamic because there are no reversals and clearance is usually quite tight.

Top ring reversals however are almost impossible to keep in full hydrodynamic lubrication because of the reversal and the high temperatures that tend to thin the oil film on the bore surface and the top ring land area.

The life of recipricating rods and hot ring packs are two main reasons to have some more wear protection headroom. When engines are pushed hard, both of these components go into an even higher severe environment. Rods under heavy WOT combustion loads will cause the MOFT to go even lower, espicially on turboed engines with boost happening at low RPM conditions. Driving around at low throttle (low laod) gives the rods a break. High loads and high RPM also gets the ring pack even hotter. Obviously these are some of the reasons that more viscosity is needed on engines in track use.

Like most things in life, viscosity is a tradeoff. Some engines and duty cycles will show incredibly low wear on fairly low viscosity oils. Going thicker in these engines does nothing to lower wear rates.

Going a grade up for anything specifying a xW-20 or less can certainly give lower wear rates in some use conditions. Wear protection headroom is a good thing ... why wouldn't it be?

 

[ZeeOSix]

I just showed that they can be.

Cherry picked.

 

[ZeeOSix]

If that's Ford's recommendation then they've done the work to make it valid haven't they? It's not some forum user making a claim that thicker is better. What's best is what's specified. Ford doesn't say xw-50 for all their engines.

The point is Ford can recommend 5W-50 in the same engine if it's used on the track vs 5W-20 if used on the streets. If there as a problem with that, they wouldn't make that recommendation. And they went up from 5W-20 to 5W-30 for the Coyote in 2021 ... and no, the parts clearances didn't change. Tight as they've always been in the Coyote engines.

MOFT also has to do with surface finish, journal size, and oil pressure.

OIl pressure has absolutely nothing to do with MOFT. Not even inside journal bearings. You should probably study up more on how journal bearings actually work. The most MOFT you can get in a journal bearing is if the oil wedge centered the bearing, which doesn't quite happen, especially in rod bearings because of the varying loads and the reciprocation of the rods. The MOFT varies with the loads. The main thing that determines MOFT between any parts is oil the viscosity and the speed of the moving parts. That's one of the major physical aspects of Tribology.

If MOFT is sufficient then why go up a grade or two? What's the tradeoff elsewhere?

As said earlier, for more film thickness to give some wear protection headroom for any anticipated driving conditions. The trade-off is maybe a slight decrease in fuel economy. In real life driving, nobody can see a fuel efficiency hit by going from xW-20 to xW-30. Nobody has a real time MOFT sensor on every moving part inside their engine, so going up a grade ensures some added protection. If someone doesn't believe in that, great ... it's not my machine, lol.

 

[siriusc1024]

Cherry picked.

See don't do that. Just because it doesn't fit with what you think doesn't mean reject it. That's what I was saying about being self-limiting and not growing.

Ever notice how an oil standard is set then there is all this talk about what the standards mean? People here aren't setting the specs. They are learning about them. There's always going to be a lag of knowledge. So when you take information and reject it you're missing out on a growth opportunity.

So I learned something, and you chose not to. What's the saying about the difference between ignorance and stupidity? Knowing and choosing not to know? You're better than that.

You can't even tell me which engines use that coating. Further, I highly doubt anyone here knew about that. I'll admit I looked it up. The reason I looked it up is because I'm not closed to the notion that 0w-20 where specified is required beyond simple parasitic losses and EPA targets. You don't have to be, either. Nobody is keeping score of who's right, and if they are then whatever.

 

[siriusc1024]

The point is Ford can recommend 5W-50 in the same engine if it's used on the track vs 5W-20 if used on the streets. If there as a problem with that, they wouldn't make that recommendation. And they went up from 5W-20 to 5W-30 for the Coyote in 2021 ... and no, the parts clearances didn't change. Tight as they've always been in the Coyote engines.


OIl pressure has absolutely nothing to do with MOFT. Not even inside journal bearings. You should probably study up more on how journal bearings actually work. The most MOFT you can get in a journal bearing is if the oil wedge centered the bearing, which doesn't quite happen, especially in rod bearings because of the varying loads and the reciprocation of the rods. The MOFT varies with the loads. The main thing that determines MOFT between any parts is oil the viscosity and the speed of the moving parts. That's one of the major physical aspects of Tribology.


As said earlier, for more film thickness to give some wear protection headroom for any anticipated driving conditions. The trade-off is maybe a slight decrease in fuel economy. In real life driving, nobody can see a fuel efficiency hit by going from xW-20 to xW-30. Nobody has a real time MOFT sensor on every moving part inside their engine, so going up a grade ensures some added protection. If someone doesn't believe in that, great ... it's not my machine, lol.

The oil leaking out of the bearing has to be resupplied. You know what happens to bearings when oil pressure drops. As long as pressure is maintained then oil pressure doesn't matter. That's supportive of using lighter weight oils. If pressure is sufficient, and it will be for 0w-20 where 0w-20 is specified, then heavier oil won't help. What thicker oils will do is heat up more at the boundary conditions, and will heat up even further as clearances decrease. That's why oil flashpoint and thermal breakdown limits are so high above typical operating temps. There's a temp gradient on the parts, especially the journals.

 

[userfriendly]

Exactly. Thin around and find out. Just not in my engines.

 

[ZeeOSix]

See don't do that. Just because it doesn't fit with what you think doesn't mean reject it. That's what I was saying about being self-limiting and not growing.

Didn't say it was wrong ... said it was cherry picked. Can you say how many and exactly what engines are using coatings that are "oil viscosity sensitive"? You found some research study program (the link goes there), and the paper says so - a study using "simulated lubrication conditions" ... not even any testing in a real fired engine. So I bet it's not even employed in any engine right now. If so, show me which engine use that technology, and where in the OM for those engines that they absolutely "require" a certain oil viscosity.

Ever notice how an oil standard is set then there is all this talk about what the standards mean? People here aren't setting the specs. They are learning about them. There's always going to be a lag of knowledge. So when you take information and reject it you're missing out on a growth opportunity.

What "oil standard" are you talking about?

You can't even tell me which engines use that coating. Further, I highly doubt anyone here knew about that. I'll admit I looked it up. The reason I looked it up is because I'm not closed to the notion that 0w-20 where specified is required beyond simple parasitic losses and EPA targets. You don't have to be, either. Nobody is keeping score of who's right, and if they are then whatever. It's ok to not know. Really.

I'd say no engines used today employ any type of coatings that are "viscosity sensitive" ... if they were that sensitive we'd know about it by now, and the engine maker would have some pretty special notes or warnings in the OM about what "required" oil viscosity to use. You ever see any OM that says a specific viscosity is absolutely "required"? They don't, they use the word "recommended". The info you found was a research program, not even doing research using a real fired engine, but simply using "simulated lubrication". There can be a far cry from that kind of research to a real engine use scenario.

 

[Hohn]

I just showed that they can be.

Not really. Read the paper more carefully. It’s saying that some DLC coatings can give slightly lower friction with lighter oil, but it’s very temperature dependent. And this is in a simulated engine environment, not an actual test.

I don’t know if anyone using DLC near top ring lands. Probably because it’s brittle and with temperature cycles on piston rings and lands would almost certainly fail.

DLC is fantastic on shafts that bear load. We use it on fuel pump cam roller follower pins.

 

[siriusc1024]

Not really. Read the paper more carefully. It’s saying that some DLC coatings can give slightly lower friction with lighter oil, but it’s very temperature dependent. And this is in a simulated engine environment, not an actual test.

I don’t know if anyone using DLC near top ring lands. Probably because it’s brittle and with temperature cycles on piston rings and lands would almost certainly fail.

DLC is fantastic on shafts that bear load. We use it on fuel pump cam roller follower pins.

It said better performance at the tested temps. It didn't say temp-dependent.

It said lower friction and less wear.

All that was in bold...

Rings:
https://www.nti-nanofilm.com/ultra-...us-carbon-tac-for-diesel-engine-piston-rings/

More rings:
"3-part composition of TOP, 2ND and OIL rings, the OIL ring is a 3-piece type"
https://www.tpr.co.jp/tp_e/products/powertrain/pistonring/

Btw, TPR is a supplier to Toyota.

They tested other coatings, as well.

 

[ZeeOSix]

The oil leaking out of the bearing has to be resupplied. You know what happens to bearings when oil pressure drops. As long as pressure is maintained then oil pressure doesn't matter.

Yes, the oil pressure just supplies the bearing, but the oil pressure does not create or even help increase the MOFT inside the bearing - that happens naturally from the bearing's rotation, and what the oil viscosity is will determine the MOFT. The HTHS viscosity is what matters between moving parts because the oil in being sheared. But the oil pressure on the bearing also does help increase the flow through the bearing above what the natural side leakage would be from it's rotational speed. So more oil pressure can help flow more oil through the bearing and help keep it cooler than if that extra flow wasn't there. This has been discussed in may threads over the years.

That's supportive of using lighter weight oils. If pressure is sufficient, and it will be for 0w-20 where 0w-20 is specified, then heavier oil won't help.

But you don't seem to understand that the MOFT inside the bearing is very dependant on the viscosity. If all other factors are constant, then higher viscosity will always create more MOFT, even in bearings with tight clearance. Again, oil supply pressure has no association with the MOFT wedge created inside the bearing. That wedge is at 1000s of PSI, and adding the supply oil pressure on top of that doesn't add anything to the MOFT.

What thicker oils will do is heat up more at the boundary conditions, and will heat up even further as clearances decrease. That's why oil flashpoint and thermal breakdown limits are so high above typical operating temps. There's a temp gradient on the parts, especially the journals.

True, tighter clearances will heat the oil up more because the shear rate on the oil increases. But with a constant clearance, the difference in the oil temperature increase between oil viscoity is minor and doesn't matter in the grand scheme. If that was such a great factor and concern, high performance engines woldn't be running thicker oil for track use. Been over all that before. Stil recall the guy who thought he's just run the 5W-20 on the oil filler cap for track use, then wondered why his rod bearings didn't last very long, lol.

 

[siriusc1024]

Yes, the oil pressure just supplies the bearing, but the oil pressure does not create or even help increase the MOFT inside the bearing - that happens naturally from the bearing's rotation, and what the oil viscosity is will determine the MOFT. The HTHS viscosity is what matters between moving parts because the oil in being sheared. But the oil pressure on the bearing also does help increase the flow through the bearing above what the natural side leakage would be from it's rotational speed. So more oil pressure can help flow more oil through the bearing and help keep it cooler than if that extra flow wasn't there. This has been discussed in may threads over the years.


But you don't seem to understand that the MOFT inside the bearing is very dependant on the viscosity. If all other factors are constant, then higher viscosity will always create more MOFT, even in bearings with tight clearance. Again, oil supply pressure has no association with the MOFT wedge created inside the bearing. That wedge is at 1000s of PSI, and adding the supply oil pressure on top of that doesn't add anything to the MOFT.


True, tighter clearances will heat the oil up more because the shear rate on the oil increases. But with a constant clearance, the difference in the oil temperature increase between oil viscoity is minor and doesn't matter in the grand scheme. If that was such a great factor and concern, high performance engines woldn't be running thicker oil for track use. Been over all that before. Stil recall the guy who thought he's just run the 5W-20 on the oil filler cap for track use, then wondered why his rod bearings didn't last very long, lol.

I do understand MOFT. So do the people designing the engines. If MOFT is sufficient then it's sufficient. There are tradeoffs. That's design optimization.

How long does stuff last on the track in general?