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.