In the present work, the heat dissipation rate and thermal resistance of electronic cooling system is investigated with different coolants by two-phase closed loop thermosyphon method for both steady and unsteady state conditions. The coolants used in this study are acetone, alcohol and petrol respectively and are poured in the created test facility. A square heater of size 35 × 35 mm is fixed in the primary tank and used as a heat source. The heat input is given to the system varies from 10 to 60 W. The temperature of the experimental setup is measured by seven K-type thermocouples which are attached at various locations. Results indicate that (i) the convective heat transfer coefficient increases and thermal resistance decreases with increasing of heat input for all the coolants (ii) the acetone has high heat removal rate of 65.4 % at 60 W due to low boiling point, high latent heat of evaporation and less effect on subcooling, which directly helps in phase change process and heat extraction rate (iii) a maximum reduction in thermal resistance of about 0.523 0C/W for acetone in comparison with alcohol and petrol by virtue of its high superheat which accelerates to nucleate boiling. © 2018 International Information and Engineering Technology Association. All rights reserved.