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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.

The major phosphorus-containing compounds in engine oil are zinc dithiophosphates (ZDP's), which act both as antioxidants and antiwear agents. To reduce engine oil phosphorus concentrations without compromising engine durability, and thereby reduce phosphorus poisoning of emission control devices, an optimum ZDP or ZDP mixture should be used. A 160 000-km taxi test was conducted to determine the relative camshaft and lifter wear protection provided by several ZDP's and ZDP mixtures. Wear protection was poorest with aryl ZDP's (which are thermally stable, as determined by differential scanning calorimetry (DSC)), intermediate with long-chain primary alkyl ZDP's (which are thermally unstable), and best with short-to-medium chain secondary or short-chain primary alkyl ZDP's (which are of intermediate thermal stability). Sequence IIID test results on analogs of the field test oils correlated fairly well with taxi test results; Sequence V-D test results did not correlate as well.

The ASTM Sequence IIC test was established to evaluate the rust and corrosion protection provided by gasoline engine oils. It is one of the several tests currently used to define SE-quality engine oils. The test utilizes a 1967, 7.0 L Oldsmobile engine which is no longer available. This paper describes the program to replace this engine with a 1978, 5.7 L Oldsmobile engine. The new test called Sequence IID also evaluates engine oil rust and corrosion protection, and it correlates with both Sequence IIC engine test and passenger car short-trip test results.

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 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 Sequence IIB rust test procedure did not provide sufficient differentiation among better quality SE engine oils. A new, more severe test, Sequence IIC, was developed to provide the improved differentiation. In general, Sequence IIC results are about one-half rust rating number lower than Sequence IIB results on minimum quality SE engine oils. Sequence IIC results correlate very well with short-trip car data obtained with either leaded or unleaded gasoline. The location and amount of rust and/or discoloration observed on lifters from short-trip car tests, conducted with either leaded or unleaded gasoline, are reproduced in Sequence IIC tests using leaded gasoline. In addition, the procedure has sufficient sensitivity to show performance changes with relatively small changes in additive concentration.