A fluid cooler assembly comprises a vertically stacked first type and second different type of tubular panel subassembly construction integrated with a third subassembly of external corrugated fin construction positioned above and below each tubular panel subassembly. The first type tubular panel subassembly has an internal central flow region configured with a bilateral linear flow channeled subregion adapted for controlling the hydraulic behavior of the internal tubular coolant fluid flow. The second tubular panel subassembly has an internal tubular central flow channel region configured with a bilateral cross-flow channel region adapted for optimizing heat transfer. The integrated third subassembly of corrugated fin construction is externally positionally fixed above and below each tubular panel subassembly and is configured to increase the fluid cooler assembly heat transfer surface area and thus improve heat transfer cooling from the internal coolant fluid to the external fluid surrounding the fluid cooler assembly.