SAE Review of Dr. Schneider's Paper

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Effect of Lubricant Properties and Lubricant Degradation on Piston Ring and Cylinder Bore Wear in a Spark-Ignition Engine, Schneider et al:

Part 1:

Let me begin by saying that every person interested in motor oil should go to SAE.org and purchase this article. (The paper was very detailed and I have tried to simplify the results. Also, I will need to report the results in several different postings so hang on please.) This research is made more relevant by actually using V-6 engines for wear testing - 1999 GM 3.4-L 60 degree block. And the radiotracer method of wear detection has been shown to be very accurate. They go on to say that cylinder wear and ring wear are perhaps the best areas to test oil and wear for engine longevity, particularly the rings.

Loads and RPMs varied during tests and for most tests the coolant and oils were artificially kept in the normal operating range for the engine. The coolant was not allowed to rise over 203 F and the oil was kept below 248 F. The basic test oil was a fully formulated 5W-30 quality oil. Comparisons were made between SJ GF-2 and SL GF-3 oils, both mineral based and synthetic oils were tested. Mineral based SJ oils were tested with varying quantities of ZDDP. Fully identical mineral based oil additive packaged SJ oils of different viscosities were compared. Wear rates were also tested compared to oil temperature.

Wear rates were determined by measuring the radioisotopes in the oil. It was noted that the accumulation in the oil filter was minimal. This shows that metals in the oil are a good way to measure wear. (Note that with cavitation wear the metal particles would be large and caught in the filter as would the larger dirt particles.)

Results of comparing GF-2 to GF-3 mineral based lubricants:

In general, wear rates were high during the start up period (20 minutes) as previously noted (1). Then a steady state of less wear was reached at 2,000 RPM and low load. There was a big increase in wear rates when the load was at wide open throttle, WOT, at 2,000 RPM. A modest increase was noted if you kept the load at WOT and increased the RPM to 4,000.

Actual numbers:
Average wear (ug/h) for 650 RPM, low load = 50, for 2,000 RPM, low load = 79.
For 2,000 RPM at WOT = 516, for 4,000 RPM at WOT = 758.

They state that wear is independent of RPM but there is a high correlation between wear and engine load. (This seems odd at first. You double the RPM but the wear does not double as long as the load is the same. The wear rate per revolution actually decreases with RPM. The overall wear may increase but it is less per revolution.)

They state that there is little concern for ring wear under typical light load conditions. (Typical city and steady state U.S. highway conditions.) They conclude that there were no differences between the SJ GF-2 and SL GF-3 mineral based oils in wear rates. This is the null hypothesis as the major difference between these oils is the newer lower volatility and increased oxidative stabililty between these oil classes.

More to come...

aehaas

(1) Effect of Break-In and Operating Conditions on Piston Ring and Cylinder Bore Wear in SI (Spark-Ignition) Engines, Schneider et al:
The rate of wear is much higher within 15-20 minutes of start-up than after reaching normal operating temperature. There was a lot of data but I conclude that the initial start-up time period (first 20 minutes) result is 100 nanometers of wear whereas the steady state wear rate was only 4 nanometers per hour thereafter. (Hence we should be concerned about start-up oil thickness more than running thickness. This justifies the statement that 95 percent of engine wear occurs just after start-up.)

Written with permission from Dr. Eric Schneider.
 
Thank you very much for providing this. Keep in mind that during start up (first 20 minutes), not only is the oil thicker, but because it's not up to full temp yet, the additives aren't working at their full effectiveness. My point is we must not automatically attribute start up (first 20 minutes) wear to viscosity related alone. Is there data showing wear during start up with same formulation but different viscosities? That would separate out the effects.
 
Thanks for the info Dr. Haas. Good stuff, there.

Quote:


because it's not up to full temp yet, the additives aren't working at their full effectiveness.




I'd have to disagree with you there JAG. Individual asperity contacts can raise local temperatures to a very high level. More than enough to activate AW/EP adds IMHO.
 
lugging engine more wear,cold engine more wear ,less wear during light load.This is what I learned in high school auto shop in 1969. Oil viscosity at startup? also pistons aren't round when they are cold the clearances are different as well as the temperature activated additives
 
Quote:


This shows that metals in the oil are a good way to measure wear




Would this then validate oil analyis as being a good way to measure wear then?
 
Several things here.

I do believe that microscopic wear at start up is mainly because of a lack of the additives doing their work. Most reactions are temperature dependent and we know that additives are used that work at different temperatures to cover the temperature range at which oils are asked to do their work. It may be that new additives are needed to cover the wear below optimal operating temperatures.

Cavitation wear, or large particle wear, is more viscosity and flow dependent. This to me is where a lot of sports cars are abused. The owners start up the car and rev it up in the garage without warming the oil. There is no load but large particles are lost by cavitation.

For microscopic wear it seems these types of research justify the use of UOA numbers, keeping in mind the large margin of error in the tests, sampling errors and the effects of sludge build up and dissolution.

aehaas
 
Would it make sense to compare startup wear between say 0w20 and 10w30 rather than SJ GF2 vs SL GF3? Or am I missing something here...
 
Quote:


Thus, to develop a theory of ZDDP AW films, it is necessary to understand the behavior of ZPs in response to the conditions encountered during asperity collision. These
conditions include pressures, p, and temperatures that
exceed the theoretical yield strength, py, and melting
point of the substrate, respectively [18].



Page 2
 
Tempest, that is another good paper on what may be happening with ZDDP.

Some of the questions above will be answered shortly with parts 2 and 3. Other questions are part of new work being done as we speak (according to Dr. Schneider.)

aehaas
 
Thanks much Dr. Haas
wink.gif


Will
 
I think it would be better to start it up and go immediately but go light on the gas. The load is low and it heats up faster. There is a big difference between a low load as is needed to drive down the road and wide open throttle, a condition that is rarely needed.

aehaas
 
Just goes to reenforce my afection for ZDDP! Nothing like it. Their are no other AW additives by themselfs that can do all the things ZDDP does for the money. Do not get me wrong I like moly,boron,tungsten and lead based AW/EP additives but I have not seen were anyof them really make up for reduceing the ZDDP levels. I still think that companies do not use enough boron based additives to make up for the reduction in ZDDP. Moly I think is a mixed bag it is good stuff but I think that too much interferes with ZDDP.
 
It's a shame that ZDDP is being reduced when Noak volatility was never considered. It's such a good multi-functional additive that is cheap, which IMO means you can spend the money elsewhere on other additives/base oils, no?
 
Quote:


It's a shame that ZDDP is being reduced when Noak volatility was never considered. It's such a good multi-functional additive that is cheap, which IMO means you can spend the money elsewhere on other additives/base oils, no?


Buster I would guess that is why zddp was used instead of higher priced additives . I don't think the $$$ saved was put back into the product.
 
Steve you're probably right.

JB, I take back what I said. boron + zddp has been shown to work better than ZDDP alone.
 
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