HT/HS, lower = slightly better fuel economy BUT

Does it really matter if at 200k miles that the engine has 20% life remaining instead of 40% life remaining when the rest of the vehicle is falling apart around it?
 
I don’t disagree with evidence provided or with the notion that thinner oils are all about CAFE. Nor do I disagree with the finding regarding engine wear and thinner oils. My question is, what is the real world impact and have we seen it?

0w16 has been spec’d for 5 years for some Toyotas. So where are dead bodies? All I see are Toyota’s plugging along like always. Maybe with “slightly worn” engines, sure, but still going reliably nonetheless.

If an engine is worn out on the way to the junk yard or buy here, pay here lot after 250K miles with a rusted out frame and clapped out suspension - who cares?

What is the point of diminishing return with analysis where it no longer has practicality? And have we reached it?
 
Does it really matter if at 200k miles that the engine has 20% life remaining instead of 40% life remaining when the rest of the vehicle is falling apart around it?
Depends on the person, and also where they live and drive the car. Not everyone owns and use cars that are subject to insane amounts of salt on the roads.
 
0w16 has been spec’d for 5 years for some Toyotas. So where are dead bodies? All I see are Toyota’s plugging along like always. Maybe with “slightly worn” engines, sure, but still going reliably nonetheless.
New cars that specify 0W-16 most likely have some design changes to better tolerate the thinner oil better. There is a reason that ILSAC GF-6 is broken down into 6A and 6B. They do not want people putting 0W-16 in anything but vehicles specifically specified for 0W-16.

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Depends on the person, and also where they live and drive the car. Not everyone owns and use cars that are subject to insane amounts of salt on the roads.

No necessarily just corrosion. Suspension, transmission, axles etc are also pretty shot at that point.
 
"There are plenty of sources that mention that as the HTHS viscosity goes down, so does the "film thickness" (ie, MOFT) and therefore the higher likelihood of increased wear."

This is exactly what I was alluding to. Read my post again. The lower the HTHS the potential for more wear, if there was less wear they would be touting it, you would see statements like "Improved fuel economy and prolong engine life with low HTHS oils". But my point is you never see this type of statement instead you always hear of a potential increase in fuel economy."

Yes, you can design an engine to use lower HTHS oils but the point being all things being equal, the lower the HTHS the potential more wear.
You don’t see statements saying that thicker oil protects better either, at least not mainstream.
 
No necessarily just corrosion. Suspension, transmission, axles etc are also pretty shot at that point.
Depends of someone wants to put some repair money into those things or not, or spend a ton of money on a different vehicle.
 
You don’t see statements saying that thicker oil protects better either, at least not mainstream.
Only people who are into oil and understand the basics relationship between moving parts and lubrication (ie, Tribology) would know. It's probably against the "CAFE Law" to advertise that thicker oil protects moving parts better. 😄 Toyota OMs try to do some of that when they say using thicker oil for certain driving conditions will better protect the engine.

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So according to this graph 2.6 HTHS is pretty solid. Let's forget about that for a moment, and only look at real world data. There are many thousands of vehicles on the road with over 200K running exclusively Xw20 oils at this point. We also know that many owners grossly extend oil change intervals, even those running "thin" Xw20 grade oils. Extending OCI's beyond manufacturer recommendation certainly has potential to increase fuel delusion and shearing making the oil even thinner. Most do all of this on whatever bargain jobber bulk oil and filter the local quick lube has in stock. Still, they motor on for many hundreds of thousands of miles.

Then you have owners like me who change oil every 5K (half of the recommended OCI) and use OE oil (meeting spec) and drive moderately. If they can make it to 200K, surely I should have little concern of an oil related failure.

Not at all trying to start a war here. I say, run what you want! I just don't buy into the line that 20 grade oils IF SPECIFIED BY MANUFACTURER will cause the early demise of your engine. We are easily on year 20+ of this and engines appear to be more reliable than ever.
 
So according to this graph 2.6 HTHS is pretty solid. Let's forget about that for a moment, and only look at real world data. There are many thousands of vehicles on the road with over 200K running exclusively Xw20 oils at this point. We also know that many owners grossly extend oil change intervals, even those running "thin" Xw20 grade oils. Extending OCI's beyond manufacturer recommendation certainly has potential to increase fuel delusion and shearing making the oil even thinner. Most do all of this on whatever bargain jobber bulk oil and filter the local quick lube has in stock. Still, they motor on for many hundreds of thousands of miles.

Then you have owners like me who change oil every 5K (half of the recommended OCI) and use OE oil (meeting spec) and drive moderately. If they can make it to 200K, surely I should have little concern of an oil related failure.

Not at all trying to start a war here. I say, run what you want! I just don't buy into the line that 20 grade oils IF SPECIFIED BY MANUFACTURER will cause the early demise of your engine. We are easily on year 20+ of this and engines appear to be more reliable than ever.
Yes, xW-20 will work fine most of the time on the streets in normal driving situations ... I've said that dozens of times in various threads discussing engine protection due to viscosity. But there is no denying that as viscosity becomes lower, and the ability of the viscosity alone loses the ability to keep moving parts separated, then increased wear can start happening. Every source of the relationship between viscosity and MOFT (basic Tribology) will conclude that fact.

However, from many sources it looks like 2.6 cP of HTHS viscosity is about where things start getting a little on the "boarder line" of protection - especially in driving conditions that would put more stress and heat into the engine. This is why I personally will use 5W-30 in any engine calling for xW-20 ... because I want some engine protection headroom so it will cover anything from going to the grocery store at less than 2500 RPM to getting on it sometimes pretty hard and using all the HP available. IMO, there is nothing wrong with some added protection insurance/headroom.
 
Yes, xW-20 will work fine most of the time on the streets in normal driving situations ... I've said that dozens of times in various threads discussing engine protection due to viscosity. But there is no denying that as viscosity becomes lower, and the ability of the viscosity alone loses the ability to keep moving parts separated, then increased wear can start happening. Every source of the relationship between viscosity and MOFT (basic Tribology) will conclude that fact.

However, from many sources it looks like 2.6 cP of HTHS viscosity is about where things start getting a little on the "boarder line" of protection - especially in driving conditions that would put more stress and heat into the engine. This is why I personally will use 5W-30 in any engine calling for xW-20 ... because I want some engine protection headroom so it will cover anything from going to the grocery store at less than 2500 RPM to getting on it sometimes pretty hard and using all the HP available. IMO, there is nothing wrong with some added protection insurance/headroom.
Certainly nothing wrong with that!
 
But studies tend to use the same test for different oils. The point above is that lower HTHS oils are generally specified for engines that have been designed to accommodate them - so don't go putting lower HTHS oil in older engines and if you put higher HTHS oils in newer engines you may improve wear above the accepted service levels but at the expense of fuel economy.

^^^^^^ This is a great reply. Right oil for the specific engine.

In the quest to run the proper oil for my 1997 Jeep Wrangler 2.5L Four-banger..... It will get Rotella Semi-Synthetic 10w30 that has a 3.5+ cP. You will never catch me pouring in the most recently spec'd 5w30, that likely has a basement cP number. There are boatloads of Jeep 2.5L owners that run T6, 5w40.

I will slightly deviate from a USA Owners manual, with the full understanding of the Australian and European Owners manual for the same, exact engine spec'ing a higher HTHS. I tend to bend to a higher HTHS when I can. Example.... my daughter owns a Turbo F150 and I do the oil changes for her. That truck will forever get a very robust 30wt oil with has high a HTHS as I can find.
 
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