Heat exchangers are used as cooling and heating equipment in industry. Shell and tube heat exchanger is one of heat exchanger consists of a shell with a number of tubes. PLTA Cirata has cooling system in the form of thrust bearing oil cooler generator. Thrust bearing oil cooler generator using shell and tube type heat exchanger one shell pass two tube pass. Oil cooler used for lubricanting oil cooler with water medium. Lubricating oil is used to cool, lubricate, and reduce vibration in the thrust bearing generator. The cooling water flowing in the tube oil cooler comes from the draft tube drainage pumped by the cooling water pump. How to get maximum oil cooler heat transfer results, it takes the temperature of lubricating oil out of the oil cooler of 36o C. From the observed data, the temperature of lubricating oil out of the oil cooler experienced the highest increase of 41o C. The analysis using Logarithmic Mean Temperature Diferential (LMTD) method. The performance of thrust bearing oil cooler generator can be seen from the calculation of the effectiveness of heat exchanger with parameters of inlet fluid temperature and outlet fluid temperature, fluid flow, fluid density, fluid heat capacity, and fluid heat transfer coefficient also cross-sectional area of the shell and tube. In commissioning data, oil cooler heat transfer rate is 297,718 kW and oil cooler effectiveness is 0.46. However, there is a decrease in current operating data obtained oil cooler heat transfer rate with an average of 175.899 kW and oil cooler effectiveness with an average of 0.272. This is due to a decrease in the temperature difference of the lubricating oil of 4o C should the temperature difference of the lubricating oil can reach 9o C. This study aims to determine the value of effectiveness and heat transfer heat exchanger rate on thurst bearing oil cooler generator at PLTA Cirata through comparison of commissioning data and current operating data.