The mitigation of boiling instabilities by using water-alcohol mixtures as coolants in a two-phase pumpless loop is experimentally investigated. Water-miscible alcohol, namely, 2-propanol, is added to water in quantities of 0.05, 0.1, and 0.2 mol fractions to reduce the bubble departure diameters. Boiling experiments are carried out in the pumpless loop involving a copper-based split-flow microchannel evaporator. Two-phase flow stability and heat transfer performance are compared between pure water and 2-propanol-water mixtures. Temperature measurements at the evaporator inlet, evaporator outlet, and condenser inlet show a considerable reduction in fluctuations when the binary mixtures are used as coolants. Therefore, the addition of a small amount of alcohol to water is proposed as a simple technique to control two-phase flow instabilities as against complex geometry modification to the evaporator, often studied in the literature. The pumpless loop with water-alcohol mixtures is a viable thermal management solution for power electronic devices that involve time-varying workloads.