During their lifetime, gears may undergo starved lubrication operating conditions. Starvation has an impact on friction between gears and leads to modified gearbox efficiency. In this article, lubricant starvation tests on an FZG test rig adapted to this condition are presented. Gears were equipped with an embedded thermocouple sensor to measure their operating bulk temperature. An experimental method to isolate the test box power loss of the FZG machine is proposed. A thermal model of this test rig draws up the power loss distribution into the test box for a nominal condition of lubrication. A numerical method based on experimental results is proposed to estimate gear power loss variation during lubricant starvation.