Abstract: A cast oil pan is connected between en engine crankcase and a lower end portion of a transmission bellhousing. Oil pan side walls each incorporate an integrally cast truss extending between an end flange of the oil pan and adjacent portions of an upper flange to stiffen the connection of the engine crankcase with the transmission bellhousing. Each truss includes a horizontal rail, a plurality of bolt columns extending between the horizontal rail and the upper flange adjacent corresponding bolt openings. Diagonal ribs extend from the oil pan flange generally toward the peripheral end flange. Oil pan bolts at the truss locations pass through the horizontal rail and the oil pan upper flange adjacent the bolt columns so that bolt clamping forces are carried through the bolt columns. The heads of the bolts are positioned below the horizontal rail accessible by power tools for securing and removing the bolts.