Transformer oil or insulating oil is usually a highly refined mineral oil that is stable at high temperature and has excellent electrical insulating properties. It is used in oil-filled power transformers, some types of high voltage capacitors, high voltage switches and circuit breakers. Its function is to insulate, suppress corona and arcing, and to serve as a coolant. The oil helps cool the transformer. Because it also provides part of the electrical insulation between internal live parts, transformer oil must remain stable at high temperature for an extended period. To improve cooling of large power transformers, the oil filled tank may have external radiators through which the oil circulates by natural convection.

dreol Fleet Plus 20W-40 is high performance diesel engine oil, which provides excellent protection against corrosive wear in all types of diesel engines. This oil is suitable for all seasons and retains high level of alkalinity during use.