A power system includes an engine having a first coolant circuit and a torque converter operatively connected to the engine and in fluid communication with the first coolant circuit. The power system also includes at least one auxiliary power unit having a second coolant circuit. The first coolant circuit is in fluid communication with the second coolant circuit.
 This invention was made with government support under the terms of Contract No. DE-FC04-2000AL67017 awarded by the Department of Energy. The government may have certain rights in this invention.