Diesel engines have significant application in transport, agriculture and power generation as prime movers for both medium and heavy-duty machinery including power generation. However, the engines convert less than 40% of fuel power to useful work with the rest being lost through the exhaust and cooling systems. Through waste heat recovery technology, the low grade heat in the cooling system can be recovered effectively with the organic Rankine cycle.   The objective of this study is to increase the efficiency of a diesel engine for fuel economy and reduce CO₂ emissions through waste heat recovery from both the cooling and exhaust systems.  Heat exchangers were designed for optimum heat recovery from both the exhaust and the coolant for a low temperature application in cereal drying. Shell and tube heat exchangers are designed and modelled using computer software. The amount of energy extracted from the exhaust is 90.5KW while that from the coolant is 95KW with the heat exchangers having an effectiveness of 0.68 and 0.58 respectively. The recovered energy is used to heat air up to 55ºC, which is directed into a cereal dryer which is designed for maize drying, but can be used for other  cereals.