The main objective of the present research work is to utilise the higher amounts of exhaust energy of the LHR engines. Three vegetable oils(neem oil, rice bran oil and karanji oil) were tested in the low heat rejection engine. An electrical heater was used to heat the thick vegetable oils or the air and the results were studied. the electrical heater energy was correlated with the energy available in the exhaust of the LHR engine, so that the electrical heater can be replaced by a heat exchanger in the actual engine. The three vegetable oils, without heating, indicated a lower brake thermal efficiency of 1-4% when compared with the standard diesel engine. When these thick vegetable oils are heated and used in LHR engines the brake thermal efficiency improves. For every vegetable oil, there is an optimum temperature at which it gives the best performance. Karanji oil operates at the maximum brake thermal efficiency(5% higher than the standard engine with karanji oil operation) at 110° C fuel temperature, Rice bran oil and neem oil gives peak performance at 80° C. For rice bran oil the improvement in brake thermal efficiency over the standard engine is 4% and standard diesel engine is 3%.