I Am Tired of Hearing Oil Must Have a HTHS of 2.9 or 3.5 or Whatever

[1sttruck]

Below is a link to a study of wear, additives and viscosity on gears, which is the 'same but different' problem regarding engine wear, but which which also has similar results. I like bounding the problem per the original questions, which is 'what is wear vs vicsocity' over some range, as statements like 'use this oil because it's good enough (and serves other agendas)' are loaded with too many assumptions.

http://gltrs.grc.nasa.gov/reports/2005/TM-2005-213956.pdf

An Experimental Investigation of the Influence of the Lubricant Viscosity and Additives on Gear Wear

5. Conclusion
In this study, the influence of lubricant viscosity and additives on the wear rate of spur gear pairs was investigated experimentally. The gear specimens from a comprehensive gear durability test program that includes seven different lubricants were inspected to demonstrate the influence of the lubrication condition on gear tooth surface wear. The results indicate that the wear rates are strongly related to the viscosity of the lubricant. Lubricants with larger viscosity result in larger lambda ratios and lower wear rates. A similar strong influence of the lubricant viscosity was previously observed for surface fatigue lives as well. An exponential relationship between the surface fatigue lives and the average wear rates was found. The data suggest that viscosity plays a dominant role. There were also considerable differences in wear amounts for three lubricants with differing additive packages but similar compositions and viscositie

 

[427Z06]

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Here it is in plain Japanese. Read the English Abtract on Page 1

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That article specifically states: "Through the engine wear tests using radioisotope tracer technique, it was clarified that an HTHS viscosity of 2.6 mPa*s was the lower limit to prevent the increasing wear", and "From the results of these investigations, it was concluded that the points of designing low friction engine oil were lowering the HTHS viscosity to 2.6 mPa*s and the addition of MoDTC"

That is about as plain as english can get.

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This is not directly related to the question but is an interesting illustration of the corelation between decreasing HTHS and increasing wear Read Pgs 93-108 Page 107 has a graph depicting measured wear as HTHS decreases.

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In this article: "Infineum recommends an after shear HTHS to 3.0 cP minimum to conform to the current 9.3 cSt KV100 limit.

Note: This is for development of specifications for Diesel Engines!! Not the average passenger car gasoline engine.

I'm with AEHaas. Nothing definitive so far, just leaps of faith from a couple of graphs and unrelated parts.

As a side note: Bryanccfshr, thanks for the comprehensive and balanced approach.

 

[Bryanccfshr]

Thank you for taking the time to read the data. As with all Data there is plenty of room for interpretation. I see a relationship in the dynamics of all reciproicating engines but can reem from the data that there is a balancing point between Fuel effeiciency and wear protection in regards to viscosity.
In the End if we stray from the factory recomended specifications(higher or lower) we need to do our homework and understnds the demand our applications put on the engines and chose oils accordingly.

 

[427Z06]

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Thank you for taking the time to read the data.

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Your welcome. Actually for me, it was about the fifth reread for these papers. I've read quite a few more, but what you presented is fairly representative of the others.

 

[savvy]

Today I saw a brand new product from Lucas. It's a fully synthetic oil stabilizer that says right on the bottle......... intended for use with todays thinner oils to reduce engine noise and wear. Hype, or fact ?!

What about the possibility of long term fatigue that may prove to be associated with using thinner oils. I can almost see the writing on the wall. Someday in the not too distant future, thin oils will be legislated for mandatory use. Our thick oils of today will be tightly controlled, and will only be sold under strict guidelines, and with strict logs.

When someone gets pulled over for a traffic infraction, they'll check your oil to make sure you are running the correct viscosity, and big fines if you get caught using the wrong stuff.

Enjoy your thick oil now, while you still can.

 

[1sttruck]

It's be nice to see an English version of the paper to look at some pecifics. Looking at the charts and tables that are in English it seems that they used an oil with a bit over 1% zinc based anti-wear additives, which is a bit higher than typical for current 5W20 oils ? In addition going from 90 deg C to 130 deg C one sees the knee move from 2.4 to 2.6, where it appears that there is no margin for piston ring wear due to the knee being pretty pronounced. Perhaps some sort of endurance testing was performed or used oil was used, but if not it indicates that one is on the edge of increased wear if fresh 5W20 with higher than typical zinc anti-wear levels is used at 130 deg C.

 

[AEHaas]

The 2001 study is worth something. It is a study for oxidation, deposits, shear and soot in diesel engines among other things. The data is from what appears to be group I motor oils. I do not see any mention of whether they are fully formulated.

• Any viscometric limits on fresh oils can discriminate against the use of more shear-stable polymers.
– As noted previously, KV100 loss and HTHS loss are related.
– The current KV100 stay in grade limits in API CH apply to oils after shear, not fresh.
• No data has been shown to support the need for increased HTHS viscosity.
– Higher HTHS viscosity will adversely impact fuel economy.
• The existing KV100 limit of 9.3 cSt minimum guarantees an after shear HTHS minimum of 3.0 cP
• No data has been shown to support higher HTHS viscosity.
• Lower HTHS viscosity improves fuel economy.

Remember that this study is using oils from the year 2000 or earlier, before the fully formulated 20 wt. oils were in use. There is useful information as with any study.

No conclusions can be made regarding the SL or SM oils of today however.

aehaas

 

[427Z06]

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In addition going from 90 deg C to 130 deg C one sees the knee move from 2.4 to 2.6, where it appears that there is no margin for piston ring wear due to the knee being pretty pronounced.

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As usual, some people see what they want to see. Looking at the chart for piston ring wear at 130°C (Fig 3) we see that wear actually decreases at 4 of the 5 tested RPMs for the 2.6 HTHS 5w20 oil versus the 3.1 HTHS 10w30 oil. And there are other graphs that show lower wear for 2.6 HTHS 5w20 oil versus the 3.1 HTHS 10w30 oil, but of course, those are ignored too.

And as AEHaas points out, these aren't fully formulated oils, so one should be careful in drawing any conclusions.

 

[Bryanccfshr]

I don't think we will have access to testing and studies with todays fully formulated oils until they are obsolete.
We will be able to determine some of the weaknesses of our current oils when the test sequences for GF5 are established.
Diesel engines are very expensive and are expected to last a very long time. With a life cycle many times longer than that of a standard automotive gasoline engine. considering that expectation the (risk of an )increase in wear of a gasoline engine can be weighed as a viable compromise to decrease the cost of ownership through fuel effeciency, the bonus being credit for good mileage with automotive regulators.

 

[427Z06]

True but diesels must be stronger to withstand the higher combustion pressures needed for ignition. Because of this, and the need to deal with soot, oils for diesels will generally have different reqirements than gasoline spark ignited passenger car engines.

 

[moribundman]

I really don't like to waste my time on the internet while vacationing, but you know how addicts behave -- espcially if there's a terminal.

A few thoughts, comments and questions.

1. As a laymen I don't know what "fully formulated oil" is. Certainly it's not just oil that's formulated and additized to enhance the inherent lubricating properties of oil? Judging by what AE Hass says, I suppose "fully forumulated oil" is a recent invention that has not existed since before API SL/SM or ca the year 2000? Please explain the meaning of "fully formulated oil" within the context of tribologists' jargon.

2. HTHS may not matter at normal operating oil temperatures as they occur with the daily driving habits of the average commuter -- you know, five miles from the garage to the office in the morning and back in the afternoon.

3. HTHS may not have any effect on wear during normal operation at street-legal speeds and without the leadfoot with that some of us have to contend.

4. VW and Audi have used since ca 1999 low HTHS (2.9 - 3.4) oil in a variety of engines, gas and diesel. VW and Audi have now, after less than six years GONE BACK to using "normal" HTHS oil (=/>3.5). While VW and Audi may be just turning out average engines showing just mediocre engineering, they have been around for a very long time and are generally not behind other makers in research and development when it comes to innovative technologies and applications.

Why have VW and Audi abandoned low HTHS oils? Were they unable to maintain the longevity the consumer has come to expect from VW and Audi engines?

- were their pre-2000 LL oils not "fully formulated"?

- did VW and Audi, despite their very close collaboration with Castrol, not know that fully formulated oils would soon become available?

- somebody, any professional tribologist, PLEASE, call VW and Audi and tell them about how wrong they are. I'd like my future used cars to be be equipped with soundly designed and optimized engines. Please help them.


My Personal Opinion:

HTHS has little or nothing to do with wear unless under extreme conditions. Under those conditions, a sufficiently high HTHS presents a safety cushion that I would rather have than lack.

As another issue, contaminant particle size and viscosity must not be ignored. Considering how many people report seeing metal flakes (!!!) in new engines during break-in (I've never seen that in any of my engines), I think it's obvious that the thinnest possible oil film is probably less than ideal. If I were to see particles in my oil with the naked eye I'd surely not want a really thin oil film. And yes, we have oil filters, but a contaminant particle must first get to the filter and might well embed itself in a soft bearing surface before it gets trapped by the filter.

When it comes to viscosity, to err on the safe side may not mean any gains, but to err on the unsafe side may mean a costly paperweight.

 

[AEHaas]

Good observations above.

Many oil tests I have seen were designed to test specific aspects of oil rather than comparing final oil products against each other. Maybe they do not want to hurt each other's feelings by testing for example a 5W-30 Mobil 1 to a Red Line or Syntec.

Often, tests are for viscosity changes. A test oil may contain only the viscosity index improver and nothing else to isolate VVI aspects such as shear stability. They may want to test detergent effects so an oil may be used that has nothing in there but detergents. Things as these make it easier to test specific oil aspects independently.

I really cannot remember any test comparing the oils we buy at the stores against each other.

I do agree that HTHS is more important as we approach the limits of oil use under the very heaviest of applications. Yet I have yet to see tests using current oils that would allow us to make statements about wear and HTHS.

aehaas

 

[Bryanccfshr]

Moribudman, That is exactly what I think but have become too entangled to say.

 

[427Z06]

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While VW and Audi may be just turning out average engines showing just mediocre engineering, they have been around for a very long time and are generally not behind other makers in research and development when it comes to innovative technologies and applications.

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Sorry, Dude. Having owned my share of VW/Audi engines, and American and Japanese designs, the Deutschland designs just require thicker oil to survive the long haul. I have a suspicion that is why so many here truly believe that engines require thick viscosities to survive. They're heavily influenced by the designs they have the most experience with, to include motorcycles and diesel trucks.

I don't know what's AEHaas's definition of fully formulated motor oil is, but my definition is an oil that has been through a significant amount of testing by engineers, chemists and tribologist and then are packaged for general consumption. Most of these papers kinda' read like researchers dumping in a little of this or that to see if there's a magic bullet of viscosity and a particular additive.

But again, we are slowly drifting to opinions, beliefs and general recollections and not with credible evidence. And even when there's evidence presented, people here ignore it and only point out the data that supports their position. (See above).

Anyway, thanks for checking in, now go out and enjoy your vacation!!

[ February 13, 2006, 09:18 PM: Message edited by: 427Z06 ]

 

[AEHaas]

Fully formulated oils are those that meet API certification and therefore contain all the usual additives we are used to seeing.

Examples are oils that are SH, SJ, SL or SM rated.

I would like to see some of these "fully formulated" oils tested. For example, test a 5W-20 against a 5W-30, a 10W-30, the 5W-40 and a 15W-50 Mobil 1. Compare the same oil brand to itself but with different viscosities. Now that would be useful information.

aehaas

 

[Bryanccfshr]

AEHaas, I would be ecstatic to see such a test myself. The issue would be cost.

I hate to take this so dfar on a tangent but here goes.. What incentive is there for marketers to do this? For that matter the SAE? Bothe are in cooperation with the automakers to design the next motor oils.

What about Automakers?
Their agenda is well known in this matter. There is no justifyable reason to spend the kind of money a measured test would garner.
The testing we see is towards the lowest safe viscosity with aims at reducing internal friction loss.
Unfortunately engineering and design is not altruistic towards perfection. It is built around a goal or business model. By testing a low Viscosity oil head to head with progressively higher viscosity oils in the same engine type what are they going to prove?

Either that the 20wts are better at protection than heavier oils(which case I think the data would be everywhere) or that although 20wt with a HTHS of 2.6 properly friction modified is adequate(for what they consider normal engine life) by stepping up the HTHS a few points the wear is improved. If the second theory is correct then it goes against the overall agenda ofpushing lower viscosity oils. Why should such a thing be published by the funders? Why would it be funded in the first place? There are probably no such tests available.

 

[AEHaas]

Let me further that often tests are at ridiculous parameters as sump temperatures of 150 C, and 75 percent load. This may have good correlation to regular use. But exactly how much?

Do a test where the oil is started at 20 C, run at 50 percent load for 30 minutes then stopped and repeated once the oil gets back down to 20 C.

Do the test over again but this time run the engine for 4 hours before shutting down.

Unfortunately these are timely and expensive tests.

aehaas

 

[427Z06]

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Either that the 20wts are better at protection than heavier oils(which case I think the data would be everywhere) or that although 20wt with a HTHS of 2.6 properly friction modified is adequate(for what they consider normal engine life) by stepping up the HTHS a few points the wear is improved.

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It's more likely the case that the distinctions you make above really doesn't significantly change the overall wear in a subject engine unless it's operated in one extreme or the other. And it may further vary depending on a particular component of the engine. A 20wt with a HTHS of 2.6 properly friction modified may show less overall wear in an engine that is driven "normally" with occasional but regular WOT operation. Whereas stepping up the HTHS a few points may only show some significant superiority when the engine is run WOT 90% of the time. The data presented in the papers above certainly give more credence to this scenario.

 

[427Z06]

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Let me further that often tests are at ridiculous parameters as sump temperatures of 150 C, and 75 percent load. This may have good correlation to regular use. But exactly how much?

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As you mentioned above, the more the test becomes patterned after the real world the more expensive the test becomes. Reading notes from the development of the test with those parameters, it is clearly intentioned as a high temperature stress test to find in a reasonable amount of time any shortcomings in the oil in question. Japanese engineers were impressed and any fear of excessive valvetrain wear by them went out the window by that test requirement.

 

[1sttruck]

"As usual, some people see what they want to see. Looking at the chart for piston ring wear at 130°C (Fig 3) we see that wear actually decreases at 4 of the 5 tested RPMs for the 2.6 HTHS 5w20 oil versus the 3.1 HTHS 10w30 oil. "

Looking at the piston ring wear the authors didn't draw conclusions about individual data points, for some common reasons. One is that there is usually noise in data, as there is in this data set. Another is that the data points are often used to establish a trend using whatever model is appropriate, where we see the authors denoting some pronounced 'knees' in the data.

Typically one would want to determine where a 'cliff' or 'knee' is, which is where results change rapidly with small changes in input. In the case of this data set we see that a modest knee at 2.4 HTHS at 90 deg C, and a very pronunced one at 2.6 HTHS at 130 deg C. Ar 130 deg C the wear at 3000 rpm changes from about 2.5 ug at 2.6 HTHS to about 7.5 ug at HTHS, for about a 3x increase. At 6000 rpm the wear increases about a factor of two from 2.6 HTHS to 2.4 HTHS, to almost 15 ug. At this temperature we don't have any margin for wear with respect to viscosity, and although the authors didn't test above 130 deg C one can reasonably assume that the knee will continue to become more pronounced and move to higher viscosity, so we don't have margin with respect to temperature either. This is with a 1.6L 4 cyl engine, which I'll assume has a modest output.

This paper supports observations of what we see recommended regarding 5W20 oils, where they are the lightest recommended, and they are recommended for fuel economy as opposed to maximum engine life/lowest engine wear.