Abstract: A system is disclosed which uses hydraulic oil to directly heat and/or vaporize a fluid, for example a cryogenic fluid. The hydraulic oil flow drives a pump which pumps the fluid through a heat exchanger where it is heated by the same hydraulic oil; therefore, the respective flow rates of the oil and fluid are directly proportional to one another and can be regulated so as to avoid freezing of the oil. The hydraulic oil pump is driven by the shaft power of the heat engine, which in turn gives off hot water and gaseous exhaust that may be utilized to further heat the fluid. The shaft power of the heat engine also drives a pump for pumping oil flowing in an auxiliary hydraulic oil circuit, which pump loads the engine so as to increase the temperature of the water coolant and exhaust.