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A five-vehicle, 64 000-km test with 7.45 litre V-8 engines was conducted to determine if synthetic engine oils provided performance sufficiently superior to that of conventional engine oils to permit longer oil change intervals. The results show better performance in two areas of deposit control; inferior performance with respect to wear protection; and essentially equivalent performance in the areas of fuel and oil economies. Based on these data, it was concluded that synthetic engine oils do not provide the necessary performance required to safely recommend their use for extended oil change intervals. In addition, a cost analysis shows that the use of synthetic engine oils, even at a change interval of 32 000 km, will essentially double the customers' cost compared with conventional engine oils at GM's current 12 000-km change interval.

The ASTM Sequence IIIC test was established to evaluate the thickening characteristics of engine oils as well as to determine their control of high-temperature deposits. It is one of several tests used to define SE-quality engine oils. This paper describes the replacement of the obsolete 1967, 7.0 L Oldsmobile engine with a 1978, 5.7 L Oldsmobile spark-ignition engine. While retaining the capability to evaluate engine oil thickening resistance and deposit control, the revised test also includes the capability to evaluate valve train wear. The valve train wear results with the new test correlate well with valve train wear observed in field tests.

A 160 000-km taxi test was run to determine the effects of low-phosphorus engine oils on engine durability. Camshaft and lifter wear, deposits, and oil-thickening were evaluated in thirty vehicles with oil-change intervals purposely extended to increase test severity. Three SAE 5W-30, SF, low-phosphorus (≈0.06 mass percent) oils and two SAE 10W-30, SF/CC, normal-phosphorus (≈0.11 mass percent) oils were evaluated. Overall engine durability and performance was satisfactory with two of the three low-phosphorus, and one of the normal-phosphorus oils, and unsatisfactory (because of high wear) with the other oils. These results demonstrate that low-phosphorus oils can be provided if further phosphorus reduction is necessary to protect emission control systems, and that current normal-phosphorus oils must be properly formulated to protect engines.