We investigate the behavior of the critical temperature T_c in superconductor/ ferromagnet / superconductor (S/F/S) trilayers in the dirty limit as a function of the ferromagnetic layer thickness d_f and the S/F interface transparency. This system is interesting due to the possibility of realization of competitive 0 and pi states. We perform T_c calculations using the general selfconsistent multimode approach based on the Usadel equations in Matsubara Green’s functions technique, and compare the results with the single-mode approximation, widely used in the literature. Both methods produce similar results for sufficiently low interface transparency. For transparent interfaces we obtain a qualitatively different T_c(d_f) behavior [1]. Using the multimode approach we observe multiple 0-pi transitions in critical temperature, which can not be resolved by the single-mode approximation. We also calculate the critical S layer thickness at given d_f when an S/F/S trilayer still has a nonzero critical temperature. Finally, we establish the limits of applicability of the single-mode approximation.