ASTM D6593 test method for evaluation of automotive engine oils
ASTM D6593 standard test method for Evaluation of Automotive Engine Oils for Inhibition of Deposit Formation in a Spark-Ignition Internal Combustion Engine Fueled with Gasoline and Operated Under Low-Temperature, Light-Duty Conditions
13. Interpretation of Results
13.1 Parts Rating Area-Environment:
13.1.1 Ensure that the ambient atmosphere of the parts rating area is reasonably free of contaminants, and the temperature maintained at 24 more or less 3°C (75 more or less 5°F).

13.1.2 Rate all engine parts except the pistons, RAC, and cylinder block under cool white fluorescent lighting exhibiting approximately 4100 K color temperature, a CRI of 62 and an illumination level of 350 to 500 fc (3800 to 5400 lx). All background and adjacent surfaces shall be flat white.

13.1.3 Rate pistons and RAC's against a white background using white fluorescent bulbs and a 100 % white deflector. Maintain the illumination level between 350 and 600 fc (3800 to 6500 lx), and measure the illumination level 355 mm (14 in.) from the desk top.

13.1.4 If multiple ratings are deemed necessary of a given part or parts, consensus rating may be used according to the following: The raters shall be from the same laboratory or from an outside rater if required (no Category 1 rater available at the lab). Report only one rating value, and this value shall be agreed to by the original rater involved. Document any consensus rating in the comment section of the test report.

13.1.5 A rater shall attend at least one ASTM or CRC Rating Workshop having VG specific or comparable hardware.

13.2 Sludge Ratings:
13.2.1 Rate the following parts for sludge deposits: RAC (2), valve deck (2), camshaft baffle (2), timing chain cover, oil pan, and oil pan baffle. Use the rating locations identified on the rating worksheets (see Annex A11). Determine the ratings using the techniques detailed in CRC Manual No. 20. Perform the sludge ratings before performing any other required ratings or measurements.

13.2.2 Average Sludge (Unweighted Average of 9 Parts):
13.2.2.1 Use the self-weighting procedure detailed as follows, to determine the sludge rating merit for each part. (1) Determine the sludge depth at each of the sites shown on rating worksheets. A site is defined as a 20-mm (0.79-in.) diameter circular area.

(2) Determine an interpolated sludge value for a designated site which exhibits more than one level of sludge depth within this area. This value is generated by multiplying each rated value's volume factor by the percentage of area covered, totaling these volume factor percentages, and comparing the total to the values given in Table 7 to determine the rating for the site. As an example, if a site was determined to be 50 % A and 50 % E, the calculation would be: 50 % of the average sludge depth factor for A (or 1.0), plus 50 % of the average sludge depth factor for E (or 16.0); that is: ([0.5 3 1.0 = 0.5] + [0.5 3 16.0 = 8] = 8.5), and the calculated site sludge depth would be a D. In the event that there are areas where it is apparent that deposits had been formed, but are no longer adhering to the part, the rating site is the closest point to the designated point which will eliminate the voided area from the 20-mm (0.79 in.) rating area.

(3) Add the total rating checks made for each line on the appropriate worksheets. These shall equal 10 or 20, depending on the part that is rated.

(4) Multiply the total rating checks made on each line by ten or five, respectively (refer to (3), to obtain the percent covered by the rated sludge depth. The grand total shall equal 100 %.

(5) Convert the percent covered by the rated sludge depth at each location to a volume factor using the procedure shown in CRC Manual No. 20.

(6) Add the volume factors on each line to determine the total volume factor. Use CRC Manual No. 12 to convert the total volume factor to the sludge merit rating.

13.2.2.2 Flaky, Bubbly Sludge Deposits - Since the occurrence of flaky, bubbly sludge deposits is thought to have a possible detrimental effect on long-term engine lubrication system performance, document the occurrence of this type of deposit in the Supplemental Operational Data section of the Final Test Report. Record the engine part(s) where this type of deposit was observed and the total percent of the surface area covered. The following is suggested wording - approximately 6 % of the (left or right) rocker arm cover was found to exhibit flaky, bubbly sludge deposits.

13.3 Varnish Ratings:
13.3.1 Preparation of Parts - Rate the following parts for varnish deposits-piston skirts (8, thrust side only) and left and right camshaft baffles. Perform the varnish ratings after the sludge ratings are completed. The rating locations and dimensions shall conform with the locations and dimensions detailed on the rating worksheets (see Annex A11). Avoid disturbing adjacent sludge deposits when the parts are being prepared for varnish ratings. Heavy sludge can be removed from a varnish rating area with a 25 mm rubber spatula prior to wiping. Wipe all parts firmly with wiping materials specified in CRC Manual No. 20. Firmly rub all wiping areas in the same direction until the surface is dry and free of sludge (until no more deposit is present on the wiping material after wiping).

13.3.2 Average Varnish (Unweighted Average of three Parts) - Use the procedure detailed as follows, to determine the varnish rating of each part:
13.3.2.1 Rate any areas where varnish deposits have been altered during disassembly or sludge removal according to deposits on the surrounding non-altered areas. Do not rate altered areas as clean.

13.3.2.2 Determine varnish ratings of all parts by comparison of the deposit on the rating location using the CRC Rust/Varnish/Lacquer Rating Scale for non-rubbing parts from CRC Manual 20.

13.4 Clogging:
13.4.1 Oil Screen Clogging:
13.4.1.1 Use the following procedure to determine the percentage of the oil screen clogged by sludge:
(1) Use a device to blow air across the screen to remove any retained oil on the screen. A suitable device can be obtained from the supplier listed in X2.1.21.
(2) Regulate the air pressure to 130 more or less 10 kPa (18.85 more or less 1.45 psig).
(3) Connect the device to the screen.
(4) Allow air to flow for 5 to 10 s.
(5) Remove the device and rate.

13.4.1.2 Flexible, transparent rating aids can be made for different surface areas so that when compared to the test screen's surface, a more accurate determination of surface clogging is possible.

13.4.1.3 Determine the percentage of the total screen opening that is obstructed with sludge and debris. Transform the oil screen results by taking the natural log (ln) of the oil screen rating plus 1; that is, ln (oil screen clogging+1). Round this value to four decimal places. Report both transformed and original result on the appropriate form(s). Where laboratory bias is determined to be significant, adjust the results for severity in accordance with the Lubricant Test Monitoring System. Round this adjusted result to 4 decimal places and convert to original units by subtracting 1 from the antilog (ex) of the adjusted result in transformed units. Record this value as the final result in original units on the appropriate form(s).

13.5 Sticking:
13.5.1 Compression Rings - Record the number of stuck compression rings. Definitions to classify the degree and type of sticking are detailed in Section 3. List both hot and cold stuck compression rings on the Test Results Summary page.

Denote hot or cold stuck rings on the Supplemental Operational Data page and include the ring location (top or second) and the piston number.

13.6 Used Oil Analyses:
13.6.1 Perform the following analyses on the used oil samples taken every 24 h and on the final drain: Viscosity at 40°C (Test Method D445), wear metals (Test Method D5185), and fuel dilution (Test Method D3525). Take samples at 0, 24, 48, 72, 96, 120, 144, 168, 192, and 216 h.

13.6.2 Fuel Dilution - Determine the fuel dilution, % mass, by gas chromatography (see Test Method D3525, with the following modifications) on the used oil samples.

13.6.2.1 Use C16 in place of C14 for the internal standard (1µL injector volume).

13.6.2.2 Presume that all components lighter than C16 are fuel.

13.6.2.3 The integrator should establish a horizontal baseline under the output curve until the leading edge of C16 is reached. Establish a second baseline extending horizontally from the output curve, at the intersection of the output curve, and the leading edge of the C16 peak.

13.6.2.4 Column details are 305 cm x 3.2 mm (10 ft x 0.125 in.) SS; and the packing material is 5 % OV-1 on Chromosorb W HP.

13.6.2.5 Increase the oven temperature from 60 to 320°C, with the rate of change of temperature controlled at 8°C/min. Hold the temperature at 320°C for 16 min to elute oil.

13.7 Additional Measurements:
13.7.1 Follower Pin Wear - Measure the wear on the pins from the followers from cylinder No. 8 intake and exhaust, using the following procedure.

13.7.1.1 Label one end of the follower with the position in the engine; 8I, 8E.

13.7.1.2 Label the opposite end of the roller pin with an arrow indicating the top of the rocker and the position of the measurement.

13.7.1.3 Using a vice to hold the rocker, punch the pins with a 5 mm (3/16 in.) diameter punch from the rockers.

13.7.1.4 Measure the wear step on the follower pins using a surface finish analyzer.

13.7.1.5 Set the machine up following the manufacturer's instructions for measuring the depth of the wear.

13.7.1.6 Place the follower pin in a V-block with the arrow up (13.7.1.2).

13.7.1.7 Lower the stylus on to the follower pin and center the pin horizontally.

13.7.1.8 Set the travel points on the machine so the stylus will transverse the length of the worn surface, starting on an unworn surface at one end and completing its trace on the unworn surface at the opposite end. Position stylus to start and finish on an area between the worn surface and the area that was pressed into the rocker body.

13.7.1.9 Take a trace.

13.7.1.10 Position the evaluation length lines to bracket the displayed wear step so the measurement will only evaluate the wear step maximum depth.

13.7.1.11 Perform the above steps for both pins.

13.7.2 Ring Gap Increase - Using the top rings from cylinders 1 and 8, clean the rings thoroughly and measure the ring gap after the rings have been installed in the master bore (7.5.5). Calculate the ring gap increase. Compensate for any ring gap adjustments made during the test. Average the results and record. Determine the maximum ring gap increase and record.