What if "low tension ring" theory is all wrong?

[Hohn]

It's been a whirlwind 24 hours. I'm coming up for air now.

This is a summation of Dr Rudnick's work in Lubricants and Lubrication (2nd ed) and also Lubricant Addtives: chemistry and applications. I was able to then ask a bunch of questions and dang if it wasn't mind-blowing in several ways. Because the conversation included so many references to specific chapters and pages of these works, I feel like a got a pretty good Cliff's Notes of these enormous volumes. I suppose perhaps the AI was gaslighting me the entire time, and I am just that gullible. But it all made sense to me as explained.


What I found most mind-blowing of all, however, was the suggestion that the modern epidemic of sticking rings might have more to do with oil oxidation and little to nothing to do with "low tension rings." After all, here on BITOG it's mostly accepted as gospel that modern engines all have "low tension rings" and these rings all suck and that's why all new engines are junk and turn into oil burners.

But what is the *mechanism* by which being lower tension would cause the rings to develop deposits? Lower tension also means narrower in thickness. The result is that the rings have lower tension because they don't need as much tension to generate the same outward sealing pressure values. "Low tension" as a standalone explanation for piston ring groove deposits and resulting oil consumption is just wholly unsatisfactory as an explanation.

So what is actually contributing to the epidemic of stuck rings?


[edit by moderator - AI image removed]



The analysis continues as follows:

**The Oxidation-Deposit Pathway Leading to Ring Glazing**

Rudnick dedicates much of Chapter 9 to oxidation and nitration tests (e.g., ASTM D943 for oxidation stability, D6594 for nitration), explaining how low HTHS exacerbates these to form deposits on piston rings. Here's the mechanism:

- **Thinner Films = Higher Temperatures**: Low HTHS allows more asperity contact, raising interfacial temperatures beyond the oil's thermal stability threshold (~150-200°C for synthetics). Rudnick notes that oils with HTHS <3.5 mPa·s oxidize 20-30% faster under shear than >4.0 mPa·s grades, as measured by pressure differential scanning calorimetry (PDSC) induction time (Ch. 9, pp. 200-205). In your engine, this manifests during cold starts (~150/year) or urban transients (25% duty), where the fixed-gear pump's initial ~15-25 psi flow can't quickly rebuild films.

- **Acid Buildup and Varnish Formation**: Oxidation produces carboxylic acids (measured by TAN, total acid number), lowering TBN reserve and catalyzing further degradation. Rudnick highlights nitration (from NOx) as a GDI-specific culprit, forming nitro-compounds that condense into lacquer-like varnish on ring faces and grooves. Low-HTHS oils exacerbate this by promoting blow-by (unburned fuel/oil mist), which dilutes the sump and thins the oil further, trapping varnish precursors against hot ring lands.

- **Ring Glazing Mechanism**: Varnish hardens into a glassy carbon layer (glazing), smoothing the ring face and reducing its scraping action on the cylinder wall. Rudnick ties this to TEOST-MHT (Thermo-Oxidation Engine Oil Simulation Test, ASTM D7097), where low-viscosity oils score <80 merit for piston deposits—indicating glaze-prone varnish buildup. In turbo-GDI engines like yours, this glazing impairs sealing, leading to blow-by escalation (lost compression, ~5-10% MPG drop) and accelerated wear (Fe/Al rise ~20% in used oil analysis). Rudnick quantifies: oils with HTHS <3.5 mPa·s show 25-40% higher deposit weights in ring-pack simulations vs. >4.0 mPa·s (Ch. 9, pp. 210-215).

So what does this suggest to me?

It suggest to me that the modern problems with ring sticking have perhaps nothing to do with "low tension" rings. But, like low tension rings, it is in fact a product of the government mandated push for CAFE and enhanced fuel economy, but ring sticking is a phenomenon of oil oxidation in the ring pack, and low HTHS oils are much worse for ring pack oxidation. If the oils below 3.5 HTHS are 25-40% worse in ring pack deposit simulations than oils that are >4.0 HTHS, then how much worse are these oils that are 2.7-2.8 HTHS in ring pack oxidation?

In other words, we seem to be mistaking correlation for causation-- that because "low tension rings" coexist with low viscosity oils and sticking rings, that the the ring sticking is *caused* by the lower tension. However, the low tension may just be coexisting with the lighter oils, which may be the real contributor to stuck rings. Especially so in dilution-prone GDI or TGDI engines where the ring pack films are even more heavily compromised by dilution that can be double what the sump dilution is.


I never considered viscosity and cleanliness to be related in this way. But I'm seeing in the "Rudnick commentaries" many smaller ways in which thicker oils lead to cleaner, happier engines-- less tendency to generate crankcase aerosols (huge for GDI), thicker films which are actually very useful at light loads, etc.

This is just one of the many aspect of this deep dive with "Dr Rudnick" that sort of blew my mind, but it was by far the most consequential, in my opinion. If anyone wants me to share other insights from this deep dive with "Dr Rudnick", just say the word and I'll put those in another thread.

 

[Bailes1992]

Isn't that pretty much already agreed here? That's why such a huge love is apparent for the likes of HPL or Valvoline Restore and Protect.

 

[I<3oil]

You use a lot of quotation marks on things that don't need them.

 

[GW.]

Great info. Love the Dr.

The deposits have always existed. Low tension rings are more sensitive to them in some designs IMO. But yes, certain oils can be used to reduce or eliminate these deposits.

 

[SC Maintenance]

Theory meets reality. Pretty sure Honda / Subaru already proved this the hard way.

Started my career in R&D then went to the field. If I had a nickel for every time a R&D guy told me what I was seeing was not possible I would have a coffee can of nickels.

Likely a knife edge of tension doesn’t work as intended. It’s overall force.

 

[travis8352]

It's been a whirlwind 24 hours. I'm coming up for air now.

This is a summation of Dr Rudnick's work in Lubricants and Lubrication (2nd ed) and also Lubricant Addtives: chemistry and applications. I was able to then ask a bunch of questions and dang if it wasn't mind-blowing in several ways. Because the conversation included so many references to specific chapters and pages of these works, I feel like a got a pretty good Cliff's Notes of these enormous volumes. I suppose perhaps the AI was gaslighting me the entire time, and I am just that gullible. But it all made sense to me as explained.


What I found most mind-blowing of all, however, was the suggestion that the modern epidemic of sticking rings might have more to do with oil oxidation and little to nothing to do with "low tension rings." After all, here on BITOG it's mostly accepted as gospel that modern engines all have "low tension rings" and these rings all suck and that's why all new engines are junk and turn into oil burners.

But what is the *mechanism* by which being lower tension would cause the rings to develop deposits? Lower tension also means narrower in thickness. The result is that the rings have lower tension because they don't need as much tension to generate the same outward sealing pressure values. "Low tension" as a standalone explanation for piston ring groove deposits and resulting oil consumption is just wholly unsatisfactory as an explanation.

So what is actually contributing to the epidemic of stuck rings?


View attachment 305152



The analysis continues as follows:




So what does this suggest to me?

It suggest to me that the modern problems with ring sticking have perhaps nothing to do with "low tension" rings. But, like low tension rings, it is in fact a product of the government mandated push for CAFE and enhanced fuel economy, but ring sticking is a phenomenon of oil oxidation in the ring pack, and low HTHS oils are much worse for ring pack oxidation. If the oils below 3.5 HTHS are 25-40% worse in ring pack deposit simulations than oils that are >4.0 HTHS, then how much worse are these oils that are 2.7-2.8 HTHS in ring pack oxidation?

In other words, we seem to be mistaking correlation for causation-- that because "low tension rings" coexist with low viscosity oils and sticking rings, that the the ring sticking is *caused* by the lower tension. However, the low tension may just be coexisting with the lighter oils, which may be the real contributor to stuck rings. Especially so in dilution-prone GDI or TGDI engines where the ring pack films are even more heavily compromised by dilution that can be double what the sump dilution is.


I never considered viscosity and cleanliness to be related in this way. But I'm seeing in the "Rudnick commentaries" many smaller ways in which thicker oils lead to cleaner, happier engines-- less tendency to generate crankcase aerosols (huge for GDI), thicker films which are actually very useful at light loads, etc.

This is just one of the many aspect of this deep dive with "Dr Rudnick" that sort of blew my mind, but it was by far the most consequential, in my opinion. If anyone wants me to share other insights from this deep dive with "Dr Rudnick", just say the word and I'll put those in another thread.

I would love to see everything you have! Ive been wanting to purchase his books for a while, especially now that he has passed

 

[Jetronic]

It's been a whirlwind 24 hours. I'm coming up for air now.

This is a summation of Dr Rudnick's work in Lubricants and Lubrication (2nd ed) and also Lubricant Addtives: chemistry and applications. I was able to then ask a bunch of questions and dang if it wasn't mind-blowing in several ways. Because the conversation included so many references to specific chapters and pages of these works, I feel like a got a pretty good Cliff's Notes of these enormous volumes. I suppose perhaps the AI was gaslighting me the entire time, and I am just that gullible. But it all made sense to me as explained.


What I found most mind-blowing of all, however, was the suggestion that the modern epidemic of sticking rings might have more to do with oil oxidation and little to nothing to do with "low tension rings." After all, here on BITOG it's mostly accepted as gospel that modern engines all have "low tension rings" and these rings all suck and that's why all new engines are junk and turn into oil burners.

But what is the *mechanism* by which being lower tension would cause the rings to develop deposits? Lower tension also means narrower in thickness. The result is that the rings have lower tension because they don't need as much tension to generate the same outward sealing pressure values. "Low tension" as a standalone explanation for piston ring groove deposits and resulting oil consumption is just wholly unsatisfactory as an explanation.

So what is actually contributing to the epidemic of stuck rings?


View attachment 305152



The analysis continues as follows:




So what does this suggest to me?

It suggest to me that the modern problems with ring sticking have perhaps nothing to do with "low tension" rings. But, like low tension rings, it is in fact a product of the government mandated push for CAFE and enhanced fuel economy, but ring sticking is a phenomenon of oil oxidation in the ring pack, and low HTHS oils are much worse for ring pack oxidation. If the oils below 3.5 HTHS are 25-40% worse in ring pack deposit simulations than oils that are >4.0 HTHS, then how much worse are these oils that are 2.7-2.8 HTHS in ring pack oxidation?

In other words, we seem to be mistaking correlation for causation-- that because "low tension rings" coexist with low viscosity oils and sticking rings, that the the ring sticking is *caused* by the lower tension. However, the low tension may just be coexisting with the lighter oils, which may be the real contributor to stuck rings. Especially so in dilution-prone GDI or TGDI engines where the ring pack films are even more heavily compromised by dilution that can be double what the sump dilution is.


I never considered viscosity and cleanliness to be related in this way. But I'm seeing in the "Rudnick commentaries" many smaller ways in which thicker oils lead to cleaner, happier engines-- less tendency to generate crankcase aerosols (huge for GDI), thicker films which are actually very useful at light loads, etc.

This is just one of the many aspect of this deep dive with "Dr Rudnick" that sort of blew my mind, but it was by far the most consequential, in my opinion. If anyone wants me to share other insights from this deep dive with "Dr Rudnick", just say the word and I'll put those in another thread.

Honestly, I thought that was understood by all who are interested in oils. It's the oxidation byproducts that cause the issues; low tension rings are just more susceptible and the placement of the top ring closer to the crown with the corrsponding higher temperatures and faster oxidation isn't helping. Wear hasn't been a pressing issue for a long time.

Next you should look into the influence of friction modifiers on needle bearings..... I'm ever getting closer to convinced that the issues with cam followers are in part due to friction modifiers causing them to slide rather than roll.

Hence I've been focusing on base oil compositions that are inherently more stable and tolerant of high temperatures. I'm happy with the no shear PAO/ester oil I got now.

 

[Sacredheals]

Yep. Which is why I only use quality oils at low intervals... I am someone to keep my car for YEARS.. I'm sure with certain oils using a lot of used oil analysis you can push it to 7500 ish miles maybe even a bit farther... But I'll take the savings I get from not using oil analysis and put it into better oils and lower intervals...

I feel bad for the people that 100% invest in used oil analysis and act as if they can dictate exactly what is going on in an engine.. They're a tool and a good one for sure but you can't act like it's gods word..

 

[Hohn]

I would love to see everything you have! Ive been wanting to purchase his books for a while, especially now that he has passed

Printed out it would likely exceed 50 pages.

Imagine you died and went to heaven and got to ask God every question about everything you never understood. It was like that, only entirely focused on oil.

Damage modeling based on cold starts, hot restarts, proportions of each, fuel consumption, dilution levels, clearances, fuel contributions, etc etc.

A couple other things I took away from it:
-- the importance of cold flow in wear mitigation is mostly a lot less than you think. As long as you are <6000cP at startup (i.e. the temperature at which your "w" value is rated, not coincidentally), the cold wear is within 5% or so. So at my functional cold max of ~ 0F, a 20w-50 and a 0w-40 have very little difference in wear during a cold start.
-- Esters really help with cold wear by preventing "dry" starts and retaining residual film better.
-- My definition of "thin" was way too thin. My conversation suggested it's not so much that >3.5 HTHS is a good thing as that <3.5 HTHS as a bad thing. Hence this as a MIN spec for euro oils until they got their own CAFE-like pressure.
-- Thicker oils like 20w-50s lower wear rate as much if not more at low load than they do at high load. This is because of the effect of shear rates on film thickness. If the water skier slows down too much, he falls in. So it's easier to ski on top of a lake of honey than on a lake of water.
-- thicker oils excel in wear prevention in many-hot-restart types of duty cycles, like running errands. This is because of the much slower drainback and thicker retained residue which leads to rapid film re-establishment at startup.
-- The fuel economy difference between a really thick 20w-50 and a thin 0w-20 is still about only 2%. So all this mayhem of thin oil is for basically a rounding error in fuel economy which if of course erased by the fact that people idle their engines all the time, wasting fuel.
-- Speaking of idling, it causes much less wear than restarts do over time. It's all about keeping those films intact and not having to re-establish them. I might be changing my practice of being so reluctant to allow idling.

 

[nascarnation]

The oils today are better than 95% of the oils from the "high tension" ring days. So I don't understand why ring belt oxidization wouldn't have been a big issue back then.

 

[Hohn]

You use a lot of quotation marks on things that don't need them.

Asterisks are not quotation marks, but I take your intended point.

 

[Hohn]

The oils today are better than 95% of the oils from the "high tension" ring days. So I don't understand why ring belt oxidization wouldn't have been a big issue back then.

Power density and top ring land temperatures.

Emissions and fuel economy (power, too, in some testing) improve as you move the top ring up closer to the top of the piston. Which means modern top rings are moved to much hotter locations.

And that's putting aside the fact that modern engines are making twice as much power per liter as older engines. Back when a 318 was 180hp, it's pretty easy to manage top piston ring temperatures spreading that across 8 pistons.

But now we have 4 even smaller pistons making 300+hp in some cases with the rings moved up higher on the piston. It's far, far more severe than it used to be.

Modern oils only got so good because they had to be. An older oil in a modern engine would be a disaster.

 

[Hohn]

Isn't that pretty much already agreed here? That's why such a huge love is apparent for the likes of HPL or Valvoline Restore and Protect.

I think you're the point here that thicker oils run cleaner in the ring packs. It's not about HPL and Restore and Protect cleaning pistons, although they can do that.

It's about why those pistons got so gunked to begin with....was it from thin oils that oxidize like crazy? Could be.

 

[GI_GRIFF]

It's been a whirlwind 24 hours. I'm coming up for air now.

This is a summation of Dr Rudnick's work in Lubricants and Lubrication (2nd ed) and also Lubricant Addtives: chemistry and applications. I was able to then ask a bunch of questions and dang if it wasn't mind-blowing in several ways. Because the conversation included so many references to specific chapters and pages of these works, I feel like a got a pretty good Cliff's Notes of these enormous volumes. I suppose perhaps the AI was gaslighting me the entire time, and I am just that gullible. But it all made sense to me as explained.


What I found most mind-blowing of all, however, was the suggestion that the modern epidemic of sticking rings might have more to do with oil oxidation and little to nothing to do with "low tension rings." After all, here on BITOG it's mostly accepted as gospel that modern engines all have "low tension rings" and these rings all suck and that's why all new engines are junk and turn into oil burners.

But what is the *mechanism* by which being lower tension would cause the rings to develop deposits? Lower tension also means narrower in thickness. The result is that the rings have lower tension because they don't need as much tension to generate the same outward sealing pressure values. "Low tension" as a standalone explanation for piston ring groove deposits and resulting oil consumption is just wholly unsatisfactory as an explanation.

So what is actually contributing to the epidemic of stuck rings?


View attachment 305152



The analysis continues as follows:




So what does this suggest to me?

It suggest to me that the modern problems with ring sticking have perhaps nothing to do with "low tension" rings. But, like low tension rings, it is in fact a product of the government mandated push for CAFE and enhanced fuel economy, but ring sticking is a phenomenon of oil oxidation in the ring pack, and low HTHS oils are much worse for ring pack oxidation. If the oils below 3.5 HTHS are 25-40% worse in ring pack deposit simulations than oils that are >4.0 HTHS, then how much worse are these oils that are 2.7-2.8 HTHS in ring pack oxidation?

In other words, we seem to be mistaking correlation for causation-- that because "low tension rings" coexist with low viscosity oils and sticking rings, that the the ring sticking is *caused* by the lower tension. However, the low tension may just be coexisting with the lighter oils, which may be the real contributor to stuck rings. Especially so in dilution-prone GDI or TGDI engines where the ring pack films are even more heavily compromised by dilution that can be double what the sump dilution is.


I never considered viscosity and cleanliness to be related in this way. But I'm seeing in the "Rudnick commentaries" many smaller ways in which thicker oils lead to cleaner, happier engines-- less tendency to generate crankcase aerosols (huge for GDI), thicker films which are actually very useful at light loads, etc.

This is just one of the many aspect of this deep dive with "Dr Rudnick" that sort of blew my mind, but it was by far the most consequential, in my opinion. If anyone wants me to share other insights from this deep dive with "Dr Rudnick", just say the word and I'll put those in another thread.

This is Gold @Hohn . If I was qualified to give you a grade (which I am not) you would get an A+ from me!

 

[rstsco]

How does the use of GDI at much higher pressure than port injection, and the use of low tension rings, contribute to the higher levels of deposits? Has a correlation been established?

I'm thankful to be switching to HPL Premium Plus PCMO in the next couple of weeks, knowing Dr Rudnick was a consultant for HPL. May he rest in peace.

 

[Sacredheals]

How does the use of GDI at much higher pressure than port injection, and the use of low tension rings, contribute to the higher levels of deposits? Has a correlation been established?

I'm thankful to be switching to HPL Premium Plus PCMO in the next couple of weeks, knowing Dr Rudnick was a consultant for HPL. May he rest in peace.

I tend to believe it's more so the fact that the systems are more sensitive... GDI engines clog causing fuel burn issues people are doing longer intervals with thinner oils.. Any weak spot that has been there is now being shown by everybody pushing limits of every single part of an engine.

 

[Jetronic]

How does the use of GDI at much higher pressure than port injection, and the use of low tension rings, contribute to the higher levels of deposits? Has a correlation been established?

I'm thankful to be switching to HPL Premium Plus PCMO in the next couple of weeks, knowing Dr Rudnick was a consultant for HPL. May he rest in peace.

Port injection means there's up to 4x more time for the fuel to vaporise than with GDI. Especially when the GDI injectors are mounted on the side is it possible for fuel droplets to get to the piston walls, and from there in the ringland and beyond. Want to guess how good fuel is not at resisting oxidation?

 

[chrisgraham]

It's been a whirlwind 24 hours. I'm coming up for air now.

This is a summation of Dr Rudnick's work in Lubricants and Lubrication (2nd ed) and also Lubricant Addtives: chemistry and applications. I was able to then ask a bunch of questions and dang if it wasn't mind-blowing in several ways. Because the conversation included so many references to specific chapters and pages of these works, I feel like a got a pretty good Cliff's Notes of these enormous volumes. I suppose perhaps the AI was gaslighting me the entire time, and I am just that gullible. But it all made sense to me as explained.


What I found most mind-blowing of all, however, was the suggestion that the modern epidemic of sticking rings might have more to do with oil oxidation and little to nothing to do with "low tension rings." After all, here on BITOG it's mostly accepted as gospel that modern engines all have "low tension rings" and these rings all suck and that's why all new engines are junk and turn into oil burners.

But what is the *mechanism* by which being lower tension would cause the rings to develop deposits? Lower tension also means narrower in thickness. The result is that the rings have lower tension because they don't need as much tension to generate the same outward sealing pressure values. "Low tension" as a standalone explanation for piston ring groove deposits and resulting oil consumption is just wholly unsatisfactory as an explanation.

So what is actually contributing to the epidemic of stuck rings?


View attachment 305152



The analysis continues as follows:




So what does this suggest to me?

It suggest to me that the modern problems with ring sticking have perhaps nothing to do with "low tension" rings. But, like low tension rings, it is in fact a product of the government mandated push for CAFE and enhanced fuel economy, but ring sticking is a phenomenon of oil oxidation in the ring pack, and low HTHS oils are much worse for ring pack oxidation. If the oils below 3.5 HTHS are 25-40% worse in ring pack deposit simulations than oils that are >4.0 HTHS, then how much worse are these oils that are 2.7-2.8 HTHS in ring pack oxidation?

In other words, we seem to be mistaking correlation for causation-- that because "low tension rings" coexist with low viscosity oils and sticking rings, that the the ring sticking is *caused* by the lower tension. However, the low tension may just be coexisting with the lighter oils, which may be the real contributor to stuck rings. Especially so in dilution-prone GDI or TGDI engines where the ring pack films are even more heavily compromised by dilution that can be double what the sump dilution is.


I never considered viscosity and cleanliness to be related in this way. But I'm seeing in the "Rudnick commentaries" many smaller ways in which thicker oils lead to cleaner, happier engines-- less tendency to generate crankcase aerosols (huge for GDI), thicker films which are actually very useful at light loads, etc.

This is just one of the many aspect of this deep dive with "Dr Rudnick" that sort of blew my mind, but it was by far the most consequential, in my opinion. If anyone wants me to share other insights from this deep dive with "Dr Rudnick", just say the word and I'll put those in another thread.

I think that OEM's trying to quickly meet ever tightening and ultimately unrealistic CAFE standards have got us to the point we are at. Looking at this from an Engineering point of view, this is a great overview of not just what is happening, but why it is happening. And also looking at this from the point of view of someone (me!) that bought a 2019 Hyundai Tucson brand new, with the 2.4L Theta II engine, it helps to validate why the design problems in this engine (GDI application, low tension rings, ring pack moved closer to the top of the piston and using a two piece oil control ring design) have to be compensated for by choosing the correct lubricant for the application and following maintenance best practices, in order for this engine to have a reasonably long service life. Thank you very much for posting!

 

[kschachn]

I think that OEM's trying to quickly meet ever tightening and ultimately unrealistic CAFE standards have got us to the point we are at. Looking at this from an Engineering point of view, this is a great overview of not just what is happening, but why it is happening. And also looking at this from the point of view of someone (me!) that bought a 2019 Hyundai Tucson brand new, with the 2.4L Theta II engine, it helps to validate why the design problems in this engine (GDI application, low tension rings, ring pack moved closer to the top of the piston and using a two piece oil control ring design) have to be compensated for by choosing the correct lubricant for the application and following maintenance best practices, in order for this engine to have a reasonably long service life. Thank you very much for posting!

It's unfortunate that we guinea pig consumers are the ones who pay for these questionable improvements. Engineering isn't cheap.

One wonders if the end user recoups sufficient individual fuel savings to compensate - including ongoing maintenance and repair costs.

 

[Jetronic]

Printed out it would likely exceed 50 pages.

Imagine you died and went to heaven and got to ask God every question about everything you never understood. It was like that, only entirely focused on oil.

Damage modeling based on cold starts, hot restarts, proportions of each, fuel consumption, dilution levels, clearances, fuel contributions, etc etc.

A couple other things I took away from it:
-- the importance of cold flow in wear mitigation is mostly a lot less than you think. As long as you are <6000cP at startup (i.e. the temperature at which your "w" value is rated, not coincidentally), the cold wear is within 5% or so. So at my functional cold max of ~ 0F, a 20w-50 and a 0w-40 have very little difference in wear during a cold start.
-- Esters really help with cold wear by preventing "dry" starts and retaining residual film better.
-- My definition of "thin" was way too thin. My conversation suggested it's not so much that >3.5 HTHS is a good thing as that <3.5 HTHS as a bad thing. Hence this as a MIN spec for euro oils until they got their own CAFE-like pressure.
-- Thicker oils like 20w-50s lower wear rate as much if not more at low load than they do at high load. This is because of the effect of shear rates on film thickness. If the water skier slows down too much, he falls in. So it's easier to ski on top of a lake of honey than on a lake of water.
-- thicker oils excel in wear prevention in many-hot-restart types of duty cycles, like running errands. This is because of the much slower drainback and thicker retained residue which leads to rapid film re-establishment at startup.
-- The fuel economy difference between a really thick 20w-50 and a thin 0w-20 is still about only 2%. So all this mayhem of thin oil is for basically a rounding error in fuel economy which if of course erased by the fact that people idle their engines all the time, wasting fuel.
-- Speaking of idling, it causes much less wear than restarts do over time. It's all about keeping those films intact and not having to re-establish them. I might be changing my practice of being so reluctant to allow idling.

Any information on how much influence viscosity has on hot restart wear prevention? Time is one factor it influences I guess?

I don't sweat automatic start/stop much on a gas engine, but when it's happening every few seconds, I do turn off the system.