A multifunctional antioxidant, antiwear and dispersancy additive for fuels and lubricants is a reaction product of a thiol-substituted diazole, such as aminomercaptothiadiazole (AMTD) or dimercaptothiadiazole (DMTD), an aldehyde and a hydrocarbon-substituted succinimide dimer. The succinimide dimer is derived from polyisobutenyl succinimide and tetraethylenepentamine which are reacted in a mole ratio of 2:1.