Dyes in gear and transmission oils

Dyes, of course are ineffective in dark oils but in light colored products give a distinctive appearance. In ATF  it has been  suggested that  if  the  lubricant were  colored, any leakage from the  transmission could  be  distinguished  from  that  coming from the engine. In such case the mechanic would known which unit to repair. Actually, colored ATF has been qualified.

If dyes are added to gear oils they should be oil soluble and also stable under the conditions of operation, such as heat and the presence of other additives. Oil soluble red dye has been used in ATF. Fluorescent dyes may also find application in transmission fluids. 

Oiliness of gear lubricants

As lubricating conditions in gear sets change from that of thick film to boundary lubrication, the oil benefits by the presence of additives. For conditions with spur gear lubrication, some agent which will provide increased lubricity or oiliness may prevent film rupture and thus maintain a low friction. Oiliness additives consist of polar materials such as fatty acids or even animal or vegetable oils. One end of such fatty acid molecules will adhere to the metal surface and resist removal by shear of the gear teeth.

Sulfurized fatty oils have also been used for oiliness additives but have not always prevented a stick slip condition in automatic transmissions. By proper choice of materials and also of the sulfurizing methods, oiliness additives are provided which are said to satisfy the requirements of automatic transmissions and yet prevent “squawking”. Also, certain Phosphorus compounds have found application in ATF as lubricity agents.