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)
10. Procedure
10.1 Weighing and Mixing Sample and Catalyst Components:
10.1.1 Weigh the clean glass sample container to the nearest mg.

10.1.2 Weigh 1.500 +/- 0.001 g of oil sample into the container.

10.1.3 Add 0.060 +/- 0.001 g each of both the fuel component and the soluble metal catalyst mixture.

10.1.4 Add 0.030 +/- 0.001 g of distilled water to the glass sample container.

10.1.5 Just prior to inserting the glass sample container into the high pressure reactor, thoroughly mix the catalyst components within the sample container by hand-rotation (approximately five rotations) and proceed immediately to 10.2. Delay may result in variation of results.

10.2 High Pressure Reactor Charging and Assembly - Immediately and rapidly assemble the high pressure reactor as shown in Fig. 2.
10.2.1 Put the aluminum insert into the high pressure reactor followed by the glass sample container and the TFE (tetra-fluoro ethylene) plastic cover disk.

10.2.2 Place the stainless hold-down spring on top of the TFE disk and the glass sample container.

NOTE 17 - The stainless steel hold-down spring not only holds down the TFE cover disk but, more importantly, prevents the glass sample container from slipping inside the high pressure reactor with consequent poor results.

10.2.3 Apply a thin coating of silicone stopcock grease to the O-ring high pressure reactor seal located in the gasket groove of the high pressure reactor lid to provide lubrication.

10.2.4 Insert the lid into the high pressure reactor.

10.2.5 Place and tighten the cap on the high pressure reactor to lock down the lid in the high pressure reactor.

10.2.6 Attach the high pressure oxygen hose and purge the high pressure reactor twice at about 620 kPa (90 psig) of oxygen to remove the air originally present in the high pressure reactor.

NOTE 18 - Avoid releasing the oxygen too rapidly by decreasing the pressure to atmospheric in no less than one minute to avoid possible foaming and overflow of the sample from the glass sample container.

10.2.7 Charge the high pressure reactor to 620 kPa (90 psig) oxygen at 21°C using an in-line precision pressure gage to monitor the high pressure reactor pressure with 1 kPa (0.12 psig). (For ambient temperatures other than 21°C, increase (or decrease) the initial pressure by 2.5 kPa (0.4 psig) for each 1°C above (or below) 21°C.)

10.2.8 Fill the high pressure reactor to the required pressure and close the inlet valve. Test the high pressure reactor for leaks by immersing in water or by using soap solution.

10.3 Oxidation - Before starting the test, bring the heating bath to the test temperature at 160°C while the stirrer is in operation. (This can be done during preparation of the sample and the high pressure reactor.)
10.3.1 Switch off the stirrer and insert the high pressure reactor into the carriages. Note the time, and restart the stirrer.

10.3.2 If an auxiliary heater is used, keep it on for the first 5 min of the run and then turn it off (Note 18).

NOTE 19 - The time for the bath to reach the operating temperature after insertion of the high pressure reactor may differ for different apparatus assemblies and should be observed for each unit (a unit may carry one, two, three, or four high pressure reactors). The objective is to find a set of conditions which does not permit a drop of more than 2°C after insertion of the high pressure reactor(s) and allows the high pressure reactor pressure to reach plateau within 15 min.

10.3.3 Allow the bath temperature to level out at the test temperature which must occur within 15 min after insertion of the high pressure reactor. Maintain the test temperature within 160°C +/- 0.3°C (Note 19).

NOTE 20 - Maintaining the correct temperature within the specified limits of 160°C +/- 0.3°C during the entire test run is the most important single factor assuring both repeatability and reproducibility of test results. If the test temperature cannot be maintained as specified, the test results should not be considered valid.

10.4 Keep the high pressure reactor completely submerged and maintain continuous and uniform rotation throughout the test. A standard rotational speed of 100 +/- 5 r/min is required; any appreciable variations in this speed could cause erratic results.

10.5 Monitor the pressure of the high pressure reactor. If a dial pressure gage is used, make readings at least every 5 min. (The maximum pressure must be reached within 15 min.) After a test period (the induction time), the pressure decreases because of oxygen absorption by oil (the break point).
10.5.1 When the oil reaches the break point, the pressure decreases rapidly. The test can be terminated as soon as sufficient information has been collected to form a tangent to the decreasing pressure trace (see 10.6) or, if desired, continued until pressure decreases to some further level.

NOTE 21 - The pressure within the high pressure reactor increases at the beginning because of gas expansion accompanying the temperature increase of the high pressure reactor. Following this rise, the pressure reaches a plateau as shown in Fig. 3. This pressure may gradually drop slightly during the test. A gradual decrease of the pressure is not unusual and does not invalidate the test.

NOTE 22 - If a break in pressure does not occur within 300 to 500 mins, the operator may elect to terminate the test. A slow decrease in pressure may result from a leak in the reactor or a very gradual oxidation process.

10.6 Record the time at which the pressure starts to decrease rapidly at the break point (Point B, Fig. 1), which is marked as the intersection of the tangent of the pressure plateau line during the final 20 min before the break point and the tangent of the pressure decrease line following the break point as shown in Fig. 1.