An additive composition comprising a graft and derivatized copolymer prepared from ethylene and at least one C.sub.3 -C.sub.10 alpha-monoolefin and, optionally, a polyene selected from non-conjugated dienes and trienes comprising from about 15 to 80 mole percent of ethylene, from about 20 to 85 mole percent of said C.sub.3 -C.sub.10 alpha-monoolefin and from about 0 to 15 mole percent of said polyene having an average molecular weight ranging from about 5,000 to 500,000, which has been reacted with at least one olefinic carboxylic acid acylating agent to form one or more acylating reaction intermediates characterized by having a carboxylic acid acylating function within their structure and reacting said reaction intermediate with an amino alkylthio thiadiazole to form said graft derivatized copolymer, and a lubricating oil composition containing same are provided.