Catalyzes the final step of fatty acid oxidation in which acetyl-CoA is released and the CoA ester of a fatty acid two carbons shorter is formed. acetyl-CoA + an acyl-CoA = a 3-oxoacyl-CoA + CoA Lipid metabolism; fatty acid beta-oxidation. Heterotetramer of two alpha chains (FadJ) and two beta chains (FadI). Belongs to the thiolase-like superfamily. Thiolase family.