with tolyltriazole being most preferred benzotriazole and tolytriazole are available under the trade designation cobratec 99 and cobratec tt 100 respectively from sherwin williams chemical company the thiadiazole used in this invention is a thiadiazole of the formula str2 where r 1 and r 2 are hydrogen or r 3 s r 3 is a hydrocarbyl group containing from 1 to 16 preferably from 1 10 carbon atoms and x is an integer from 0 3 the hydrocarbyl groups include aliphatic alkyl or alkenyl and alicyclic groups which may be substituted with hydroxy amino nitro and the like preferably however the hydrocarbyl group is alkyl with nonyl being particularly preferred the most preferred thiadiazole is 2 5 bis nonyl dithio 1 3 4 thiadiazole wherein r 1 and r 2 are both r 3 s r 3 is nonyl and x 1 which is available from amoco chemicals corporation under the trade designation amoco 158 the relative amounts of benzotriazole and thiadiazole used in this invention are not critical provided that the thiadiazole is present in an amount sufficient to solubilize the benzotriazole and form a homogeneous product while the precise amount of thiadiazole present in the product can vary broadly generally greater than 50 wt preferably greater than 40 wt thiadiazole will be present to ensure the product remains homogeneous during storage at ambient conditions generally from 1 to 40 wt of the benzotrizole and from 60 to 99 wt of the thiadiazole are used in this invention while the benefits of this invention are applicable to a wide variety of lubricants this invention is particularly suitable to power transmission fluids such as.