Where Did the Notion Come From that Oils with HTHS Below 3.5 Were Unacceptable for Wear Control?

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So I have been looking for this. I did not find it in the “Taxi Study” often referred to. However, there was a paper from the 1990’s that may shed some light - Properties of Engine Bearings Lubricated with Low HTHS Viscosity Oil, 980702, Ono et al.

Experimental, not fully formulated oils, were used having API SG quality additives mixed into paraffin mineral oils. The variable was the amount of a viscosity index improver to adjust HTHS between 1.8 and 3.0. The kinematic viscosity ranged from 5 to 11. The test engine was an in-line gasoline engine with an unbalanced weight on the shaft that varied the load by RPM, around 6,000 RPM.

Oil feed (sump) temperatures were approximately 150C during the runs and had to be artificially heated with the thinner oils to keep up the temperature. Bearing temperatures were a maximum of 180C.

Results:

Wear was steady from a HTHS of 2.5 to 3 but doubled when the HTHS was lowered below 2.5 to 1.8.

Wear decreased with decreasing clearances of the bearings. Of the several bearing composits tested, the aluminum-tin-silicon variety had the least wear. (We already know that smoothness is associated with less wear as well. These sorts of things contribute to the production of engines “designed” for thinner oil usage).

They concluded that the HTHS viscosity rather than the kinematic viscosity is the only aspect that determines wear. (I have problems with this statement as they are closely and directly related).

My thoughts:

They used oil formulations not specifically designed for the emerging engines running 20 grade oils.

They used non fully formulated experimental oils using SG rated components. Newer specifications have come a long long way since then. Base oils alone can account for superior performance.

Who drives around with sump temperatures at 304F? A constant sump temperature of 302F is one heck of a severe and certainly unrealistic condition for any passenger car. Even then, if for a short period of time your sump did get that high, the wear rate according to this study, would only double. It would not be 10x or 100x more. And all this for a HTHS of 1.8.

Running the engine in a severly unbalanced condition is certainly much worse than in any balanced engine. So whereas a HTHS may show elevated wear when at 1.8 it would unlikely do so in a normal engine.

And if HTHS is the only number that counts, let’s use 20 grade oils with the higher HTHS values. The thinner kinematic viscosity will help us gain some HP and fuel economy. Who doesn't want this?

People have stated they use oils having HTHS above 3.5 to give them headroom. I believe that anything at or above 2.5 already has plenty of headroom given todays lubricants. Sure, if you have 20% fuel dilution your oil may drop below a HTHS of 1.8. But even then, todays oils should save your ...

Away with 30 and 40 and 50 and 60 grade oils. Use oils based only on HTHS. One of my favorite oils is Renewable Lubricants Inc. where their 20 grade oil has a HTHS of >2.9 accoring to their own specs. And we know it will perform well in a Ferrari Enzo that specs a 60 grade oil, in non track use.

Viscosity index improves of that time were not as good as those of today. Early, excessive thinning of their experimental oils was an issue for certain.

ali
 
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When? when the fuel in the oil in the wife's car showed 5% and the bearings failed at 60k miles requiring a freebie new engine from the manufacturer
 
This study, and a host of others, leads to misunderstanding by many folks because they don't pay for the study and actually read it. They just read the summary and make illogical conclusions because they're not aware of the conditions set forth in the test.

This study, as with many, runs the simulation in an unrealistic condition (not typical of normal daily operation) and then proclaims "Aha! Eureka - we've discovered something useful!" Nothing could be further from the truth for the common man. As Haas noted, who runs an engine with the oil sump at 304F all the time? Who runs an unballanced load on the crank? Who runs incompletely formulated oils in the daily driver?

Reminds me of the infamous GM filter study; so far from reality it's laughable.
 
Hard to imagine that modern thinking minds are basing present thoughts about oil HTHS from that far ago. A unrealistic temperature test with API SG oil.
 
When I had joined this site 20 years ago I think the HT/HS of 3.5 was considered ideal due to the oils and OEMs recommending those oils. They were often the European grades required for some of the high performance engines.
Yep, and the 3.5cP minimum was for Autobahn use and spec'd by many, if not all, Euro OEM's at the time.

On this side of the pond your typical xW-30 had an HTHS of around 3.0cP.

The study I recall was the Honda one with respect to going thinner than xW-20, where they talked about having to go with wider bearings to keep wear at an acceptable level. The 0W-16, 0W-12 and 0W-8 grades presented challenges in this department with traditional width bearings. @Shannow posted on this extensively.
 
One thing to consider too is that many modern engines have small high reving turbo's, and stop start engines, and fuel dilution due to direct injection, putting engine oils under more high temperature/high shear stress than ever, while at the same time automakers keep recommending oil viscosities with lower and lower HTHS #'s to reduce the Automaker's CAFE fines. This seems problematic, at least on paper. As a car owner, you can choose to not let this insanity affect your car. You can use a HTHS of >= 3.2 and be unaffected by all the risks of this issue (Since nearly every engine in the US that is speced for ultra low viscosities is also speced for 5W-30 and even 5W-40 in Europe and Australia).
 
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I have actually learned something here. Again, I will still look for as thin an oil as I can get during the start up period (kinematic viscosity). This is because I feel it is best to get more flow before my engine goes into bypass. And I like high RPM. At my usual start up my oil is in bypass at 3,000 RPM by the time I get out of my neighborhood (redline = 9,000 RPM). I feel oils with a HTHS of say 2.5 is fine for my engines.

So the mission will be to find the lowest viscosity at 40C while the HTHS is around 2.5 or so. Looking for a 30 or 40 or 50 grade oil, as many seek, is not in the equation. Now I feel those numbers are essentially useless. Higher grades do not necessarily guarantee higher HTHS, you have to look at the actual specs (as many here already do). I do think that insisting it is >3.5 is unnecessary. The real number, and it has headroom in my book, is 2.5. I reserve the right to lower this number with forthcoming oils however...

I do think the data has some value. It indicates that HTHS is something to look at. I admit this. But I believe that a HTHS of 1.8 or even 1.6 is probably OK for most modern engines using modern lubricants. Though personally I might go for slightly higher values as my cars often have fuel dilution issues.

Ali
 
People who think this topic is silly are likely to end up with oil consumption in the future.
Before it was total'd in a wreck, my wife's 2005 Grand Marquis would beg to differ. After a quater-million miles, the engine ran great, had no major maintenance issues, and didn't consume oil. My 2007 Grand Marquis also did just as well.

The ol' 4.6L mod-motor is very easy on oil in the 2v configurations. All on 10k mile OCIs, 5w-20, mostly conventional oil. Some engine designs are very robust, some not. 281 cubes with only 225 hp doesn't exactly qualify as high-stress ...
The "dino" oil in this UOA series was the Rural King brand; about as cheap an oil as one could buy back then. I'm sure it's HTHS rating was not impressive by any means, though I'm not sure what the actual value would be, but at $1.29/qrt, there little reason to think it was "robust" oil. And yet, it did a fine job protecting the engine, even out to 10k miles repeatedly.

I've seen 5w-20's all the way up to 10w-40's all do well in the old Ford mod-motors (2vs). That engine series just isn't susceptible to viscosity/HTHS concerns in normal use. That engine series could not care less what lube is used, as long as it's reasonbly appropriate for the application. Clearly, some "thin" oils do quite well in some "good" engines.

However, a poorly made lube in a poorly designed/built engine will never end well. There are other engines that don't fare well at all, regardless of what oil is in the crankcase. Some are just trouble prone. And no amount of HTHS would save them.


As both lubes and engines have improved over the years, I think the HTHS topic has lost some of it's zing; it's just not as important as it was decades ago.
 
One thing to consider too is that many modern engines have small high reving turbo's, and stop start engines, and fuel dilution due to direct injection, putting engine oils under more high temperature/high shear stress than ever, while at the same time automakers keep recommending oil viscosities with lower and lower HTHS #'s to reduce the Automaker's CAFE fines. This seems problematic, at least on paper. As a car owner, you can choose to not let this insanity affect your car. You can use a HTHS of >= 3.2 and be unaffected by all the risks of this issue (Since nearly every engine in the US that is speced for ultra low viscosities is also speced for 5W-30 and even 5W-40 in Europe and Australia).


Australia is recommending 0W-20 and 0W -16 now. The times are changing.
 
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