Originally Posted by ZeeOSix
^^^ Interesting ... thanks for the additional info out of the paper. I see that the fresh oil is the only one with no Moly - all the others do have it. Was all the used oil the same brand & viscosity? Apparently, the fresh oil wasn't the same formulation since it's missing Moly. The used oils are more viscous too, which could have influenced the wear seen in the test.
There were other anomalies in the oils used. As you note, no moly in the fresh sample of RO207 and notice boron shows up in the 10K and 15K samples of this oil. It appears that whatever RO207 was went through two formulation changes during the test. RO243 had 345 ppm boron in the fresh oil and a nominal 60 ppm in all the rest of the samples. The only oil that showed a consistent chemistry for all tests was RO208, which by the way thickened from SAE 20 to SAE 50 at 15K miles.
There were 3 taxis, all new at the start of the test. Each one ran one of the three test oils throughout the test. The oil was drained at the end of each test mileage. Wear was measured on a motored single cam lobe and tappet bench rig. The shims were irradiated to form cobalt 56. The amount of cobalt 56 in the oil is a direct measurement of wear.
I can't believe that they apparently didn't secure enough oil of the same batch to run the entire set of test intervals(40,500 miles). At least they weren't stupid enough to use UOA data to measure wear.
The scope of the experiment was only to see if used oil, out to 15K miles would still form a tribofilm. It had nothing to do with determining wear rates of new vs used oil in an engine. Their methodology prevents any such conclusions from being drawn. A single shim was used for each oil. The fresh oil was always run first on the new shim. Break in wear of the shim to the cam was an uncontrolled variable. There was no previous tribofilm in place on the shim when the fresh oil was run.The fresh oil was never exposed to combustion products or oil containing combustion products for the duration of the run. Combustion products are thought to be part of the formation of the lower friction and wear tribofilms formed in the presence of used oil.
Ed
^^^ Interesting ... thanks for the additional info out of the paper. I see that the fresh oil is the only one with no Moly - all the others do have it. Was all the used oil the same brand & viscosity? Apparently, the fresh oil wasn't the same formulation since it's missing Moly. The used oils are more viscous too, which could have influenced the wear seen in the test.
There were other anomalies in the oils used. As you note, no moly in the fresh sample of RO207 and notice boron shows up in the 10K and 15K samples of this oil. It appears that whatever RO207 was went through two formulation changes during the test. RO243 had 345 ppm boron in the fresh oil and a nominal 60 ppm in all the rest of the samples. The only oil that showed a consistent chemistry for all tests was RO208, which by the way thickened from SAE 20 to SAE 50 at 15K miles.
There were 3 taxis, all new at the start of the test. Each one ran one of the three test oils throughout the test. The oil was drained at the end of each test mileage. Wear was measured on a motored single cam lobe and tappet bench rig. The shims were irradiated to form cobalt 56. The amount of cobalt 56 in the oil is a direct measurement of wear.
I can't believe that they apparently didn't secure enough oil of the same batch to run the entire set of test intervals(40,500 miles). At least they weren't stupid enough to use UOA data to measure wear.
The scope of the experiment was only to see if used oil, out to 15K miles would still form a tribofilm. It had nothing to do with determining wear rates of new vs used oil in an engine. Their methodology prevents any such conclusions from being drawn. A single shim was used for each oil. The fresh oil was always run first on the new shim. Break in wear of the shim to the cam was an uncontrolled variable. There was no previous tribofilm in place on the shim when the fresh oil was run.The fresh oil was never exposed to combustion products or oil containing combustion products for the duration of the run. Combustion products are thought to be part of the formation of the lower friction and wear tribofilms formed in the presence of used oil.
Ed
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