A dual mode, vehicle thermal management system (100,200) comprising: a refrigeration subsystem; a passenger cabin subsystem; a drive train subsystem; a battery subsystem and a control system; further comprising a first coolant loop in thermal communication with the battery subsystem, said first coolant loop comprising a first circulation pump for circulating a coolant within said first coolant loop, said first coolant loop further comprising a first coolant reservoir; and a second coolant loop in thermal communication with at least one drive train component of the drive train subsystem, said second coolant loop comprising a second circulation pump for circulating said coolant within said second coolant loop, characterized by a dual mode valve system as a four-way cylindrical, butterfly or ball valve or as a first three-way valve and a second three-way valve, wherein said first coolant loop operates in parallel with and separate from said second coolant loop when said valve system (249; 401, 403) is configured in a first mode, and wherein said first coolant loop is serially coupled to said second coolant loop when said valve system (249; 401, 403) is configured in a second mode depending upon both the external environment and the immediate operating characteristic of the drive train components, allows thermal and performance optimization of vehicle's subsystems (101,103,105,107) which leads to improved efficiency and associated operating cost saving; wherein the control system is configured to automatically control the dual mode valve system (249,401,403) based on the operating characteristic of the vehicle components and ambient conditions, all of which are monitored by the control system; wherein said second coolant loop further comprising a second coolant reservoir, wherein said coolant is allowed to flow between said first and second coolant reservoirs. a refrigeration subsystem; a passenger cabin subsystem; a drive train subsystem; a battery subsystem and a control system; further comprising a first coolant loop in thermal communication with the battery subsystem, said first coolant loop comprising a first circulation pump for circulating a coolant within said first coolant loop, said first coolant loop further comprising a first coolant reservoir; and a second coolant loop in thermal communication with at least one drive train component of the drive train subsystem, said second coolant loop comprising a second circulation pump for circulating said coolant within said second coolant loop, characterized by a dual mode valve system as a four-way cylindrical, butterfly or ball valve or as a first three-way valve and a second three-way valve, wherein said first coolant loop operates in parallel with and separate from said second coolant loop when said valve system (249; 401, 403) is configured in a first mode, and wherein said first coolant loop is serially coupled to said second coolant loop when said valve system (249; 401, 403) is configured in a second mode depending upon both the external environment and the immediate operating characteristic of the drive train components, allows thermal and performance optimization of vehicle's subsystems (101,103,105,107) which leads to improved efficiency and associated operating cost saving; wherein the control system is configured to automatically control the dual mode valve system (249,401,403) based on the operating characteristic of the vehicle components and ambient conditions, all of which are monitored by the control system; wherein said second coolant loop further comprising a second coolant reservoir, wherein said coolant is allowed to flow between said first and second coolant reservoirs.