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The wear protection performance of unique boundary chemistry (UBC), both while in the engine and after removal, was tested with reference to commercial API SG, API SH/ILSAC GF‐1, and API SJ/ILSAC GF‐2 quality oils in two 80,450 km field tests, in modified and standard sequence tests, and in radiotracer engine studies. The radiotracer tests of UBC added to an API SJ/ILSAC GF‐2 quality oil replicated previously published results of wear reductions achieved in a comparison of an API SH/ILSAC GF‐1 oil with and without UBC. In extended Sequence IIIE runs, two engines, each lubricated with the same API SH/ILSAC GF‐1 oil, were unable to complete the tests as a result of excessive oil consumption due to hot stuck rings. In contrast, two Sequence IIIE engines lubricated with the same API SH/ILSAC GF‐1 oil treated with UBC completed the extended test without incident, even though the UBC‐treated API SH/ILSAC GF‐1 oil replaced the API SH/ILSAC GF‐1 oil for the first oil drain interval only. A fully formulated SAE 5W–30 oil, which contained a full complement of UBC (20%), met all the requirements of API SH/ILSAC GF‐1 quality and gave very low average and maximum cam and cam plus lifter wear on standard ASTM Sequence VE and IIIE tests. The same API SH/ILSAC GF‐1 oil without UBC gave somewhat higher wear on both tests, but both oils met API SH/ILSAC GF‐1 requirements. Wear metals analysis of a field test of 36 taxicabs, which compared an API SJ/ILSAC GF‐2 quality oil to the same oil treated with UBC for the first drain interval, and also to a UBC‐treated oil at every oil change, showed a reduction in the rate of used oil Fe accumulation for both methods of UBC treatment. This test also revealed a striking impact on Fe levels from Si found in used oil samples during an episode of Si contamination in local gasoline supplies. Finally, in a field test of 10 taxicabs, with parts measured before and after testing, wear reductions were observed in rings and bearings in UBC‐treated cabs compared to those with API SG oil alone.

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