Most of the rotating equipment in engineering, from the reduction gears to small pumps, was lubricated with a light oil known as 2190TEP. It was a fairly light-looking oil.
Oil samples were supposed to be taken daily. Sample jars were kept in three-tiered racks that sort of looked like this two-tiered one:
If my memory serves me, the top rack was for a sample of the oil that was put into the machinery on the last oil change. The next bottle down was the oil sample for that day, which was marked with a china marker (date, time and initials of the sample-puller). The third bottle was for the previous day's sample. The rack was kept in public view within the machinery space, where everyone could see it. One could then see that the samples were being pulled properly and whether or not there was any contamination of the samples.
Keeping the sample racks current was a sign of how squared-away the engineers were. It was amazing how many ships weren't. I know of one case where the engineer of a really new Spruance sent his senior engineers for tours of an Adams-class DDG in order to see how to do things properly.
If you were one of the squadron's lackeys, noticing that the sampling wasn't being done properly was an indicator that maybe the engineering department deserved closer scrutiny. Which was a version of the "500 yard rule" (if the ship didn't look good from 500 yards away, there were problems).
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