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.
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.