A.c. susceptibility, X-ray diffraction (XRD), SEM and porosity studies have been performed on Bi1.6Pb0.4Sr2Ca2Cu3-xCoxOy (x=0, 0.05, 0.1) superconductors. XRD and SEM results have shown that (i) the compound with x=0 contains mixed phases of 2223 and 2212, (ii) the increase in concentration of cobalt (from x=0 to 0.1) helps the compound to attain a structure of strong 2201 and a small amount of Ca2CuO3 impurity phase. The onset temperatures of the diamagnetic signal of these superconductor samples with x=0, 0.05, and 0.1 as observed from a.c. susceptibility measurements are 106, 60 and 50 K, respectively. The highest onset temperature, 50 K, observed in the sample with x=0.1 rather than the usually reported value of 20 K associated with 2201 phase in bismuth oxide compounds, may be due to the presence of Ca2CuO3 impurity phases. SEM and porosity results show that the cobalt helps to increase the grain and pore sizes.