The 12-stage FZG test (A/8,33/90) was originally developed to determine scuffing load capacity of engine oils [1]. During each load stage, the test is started at the same initial sump temperature. Heat of friction generated during a load stage results in a temperature increase of the lubricant. Final sump temperatures as high as 140 °C are often reached after the final load stage (Load Stage 12). A modified version of the test, (A/2,76/50) is used for laboratory determination of open gear grease performance [2]. In open gear lubrication, typical gear operating temperatures are in the range 50°C–80°C. Test temperatures higher than this may give rise to different wear characteristics than would be found under typical operating conditions. It would therefore be of practical interest to have a laboratory-based means to determine the temperature-dependent characteristics of an open gear lubricant. A compact heat exchanger was designed, built and inserted in the FZG test bed. By manipulating the flowrate of an external cooling medium, the temperature of the test fluid in the sump can be maintained at a desired temperature. Results for four representative open gear lubricants were obtained using the constant temperature test and compared with results obtained with the conventional test. These results indicated that the new test can discern between samples that perform similarly during the conventional test.

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