pendinginan adalah air yang dipompakan Cooling wa ter pump sehingga terjadi perpindahan panas dari temperatur rendah (air dari Cooling tower) mendinginkan temperatur tinggi (oli dari thrust bearing). Perpindahan panas pada sistem pendingin ini yaitu perpindahan panas secara konveksi. Apabila Oil Cooler mengalami kegagalan fungsi pada saat unit beroperasi, maka akan menyebabkan panas berlebih pada Thrust Bearing. Hal ini akan mengakibatkan kerusakan pada peralatan, terutama pada sistem bantalan (bearing) dan poros turbin. Jika hal ini berlanjut maka dapat mengakibatkan unit trip. Untuk mencegah terjadinya hal tersebut pada Oil Cooler maka perlu adanya Preventive Maintenance yaitu pemeliharaan peralatan secara berkala yang benar di saat yang tepat berdasarkan informasi yang dikumpulkan melalui pemantauan kondisi untuk mengoptimalkan kinerja dan umur peralatan. Setelah didapat hasil dari sebelum sesudah Preventive Maintenance data tersebut di hitung dengan mengunakan metode LMTD (Logarithmic Mean Temperature Difference) yaitu rata-rata logaritmik dari perbedaan suhu antara panas (pelumas) dan dingin (air) di setiap akhir Oil Cooler. Dari hasil perhitungan tersebut kita dapat membandingkan perbedaan panas yang di transfer oil cooler yang dimana semakin besar LMTD, maka semakin bannyak panas yang di transfer. Dimana hasil sebelum preventive maintenance oil cooler yaitu 10,969oC, 11,434oC, 11,434oC. dengan nilai rata-rata logaritmik (LMTD) sebelum preventive maintenance 11,279oC dan data sesudah perawatan preventive maintenance oil cooler yaitu 9,966oC, 10,428oC, dan 10,969oC. dengan nilai rata-rata logaritmik (LMTD) pada oil cooler 10,454oC. dari hasil preventive maintenance oil cooler terjadi penurunan temperature pada pelumas sehingga pelumas yang keluar dari oil cooler temperaturnya sudah turun, dan membuat temperature thrust bearing juga turun. Sehingga turbin dapat menaikan pembebanan.

Oil Cooler is one of the equipment of the cooling system which serves to cool the oil used to lubricate and cool the Thrust Bearing. The media used for cooling is the pumped water. Cooling wa ter pump so that heat transfer occurs from low temperature (water from the cooling tower) cools the high temperature (oil from thrust bearing). Heat transfer in this cooling system is heat transfer by convection. If the Oil Cooler has a malfunction when the unit operates, it will cause excessive heat on the Thrust Bearing. This will cause damage to the equipment, especially in the bearing system and turbine shaft. If this continues, it can result in a unit trip. To prevent this from happening in the Oil Cooler, it is necessary to have Preventive Maintenance, which is the maintenance of the equipment at the right time at the right time based on the information collected through monitoring conditions to optimize the performance and life of the equipment. After obtaining the results from before after Preventive Maintenance, the data is calculated using the LMTD (Logarithmic Mean Temperature Difference) method, which is the logarithmic average of the temperature difference between heat (lubricant) and cold (water) at each end of the Oil Cooler. From the results of these calculations we can compare the difference in heat transferred in the oil cooler where the greater the LMTD, the more heat is transferred. Where is the result before preventive maintenance oil cooler is 10.969oC, 11.434oC, 11.434oC. with a logarithmic average value (LMTD) before preventive maintenance 11,279oC and data after preventive maintenance oil cooler treatments namely 9,966oC, 10,428oC, and 10,969oC. with a logarithmic average value (LMTD) at oil cooler 10,454oC. From the results of preventive maintenance, the oil cooler has a temperature drop in the lubricant so that the lubricant coming out of the oil cooler has dropped, and the temperature thrust bearing also drops. So that the turbine can increase loading.