ASTM D4742 Test Method for Oxidation Stability of Gasoline Automotive Engine Oils
ASTM D4742 Standard Test Method for Oxidation Stability of Gasoline Automotive Engine Oils by Thin-Film Oxygen Uptake (TFOUT)
4. Summary of Test Method
4.1 The test oil is mixed in a glass container with three other liquids that are used to simulate engine conditions: (1) an oxidized/nitrated fuel component (Annex A2), (2) a mixture of soluble metal naphthenates (lead, copper, iron, manganese, and tin naphthenates (Annex A3)), and (3) distilled water.

4.2 The glass container holding the oil mixture is placed in a high pressure reactor equipped with a pressure gage. The high pressure reactor is sealed, charged with oxygen to a pressure of 620 kPa (90 psig), and placed in an oil bath at 160°C at an angle of 30° from the horizontal. The high pressure reactor is rotated axially at a speed of 100 r/min forming a thin film of oil within the glass container resulting in a relatively large oil-oxygen contact area.

NOTE 1 - A pressure sensing device can be used in place of a pressure gage.

4.3 The pressure of the high pressure reactor is recorded continuously from the beginning of the test and the test is terminated when a rapid decrease of the high pressure reactor pressure is observed (Point B, Fig. 1 ). The period of time that elapses between the time when the high pressure reactor is placed in the oil bath and the time at which the pressure begins to decrease rapidly is called the oxidation induction time and is used as a measure of the relative oil oxidation stability.

5. Significance and Use
5.1 This test method is used to evaluate oxidation stability of lubricating base oils with additives in the presence of chemistries similar to those found in gasoline engine service. Test results on some ASTM reference oils have been found to correlate with sequence IIID engine test results in hours for a 375 % viscosity increase. The test does not constitute a substitute for engine testing, which measures wear, oxidation stability, volatility, and deposit control characteristics of lubricants. Properly interpreted, the test may provide input on the oxidation stability of lubricants under simulated engine chemistry.

5.2 This test method is intended to be used as a bench screening test and quality control tool for lubricating base oil manufacturing, especially for re-refined lubricating base oils. This test method is useful for quality control of oxidation stability of re-refined oils from batch to batch.

5.3 This test method is useful for screening formulated oils prior to engine tests. Within similar additive chemistry and base oil types, the ranking of oils in this test appears to be predictive of ranking in engine tests. When oils having completely different additive chemistry or base oil type are compared oxidation stability results may not reflect the actual engine test result.

5.4 Other oxidation stability test methods have demonstrated that soluble metal catalyst supplies are very inconsistent and they have significant effects on the test results. Thus, for test comparisons, the same source and same batch of metal naphthenates shall be used.

NOTE 2 - It is also recommended as a good research practice not to use different batches of the fuel component in test comparisons.