lubricating oil

plural lubricating oils

1. An oil for lubrication of engines and other components.

   Safety devices ensure that the engines are automatically shut down in the event of overspeed, low pressure in the lubricating oil system, low cooling-water pressure, or high cooling-water temperature.

   1955 October, “Main-Line Diesel-Electric Locomotives for Ireland”, in Railway Magazine, page 718

   1 more example

   Diesel maintenance schedules are benefiting from work done on the magnificent Hilger & Watts electronic spectrograph for oil analysis, which detects minute quantities of metals in samples of used lubricating oil; [...].

   1960 June, “Talking of Trains: New B.R. research laboratory”, in Trains Illustrated, page 329