Abstract: An oven for testing fluid samples to determine the effects of temperature and various chemical additives on the rheological, filtration and chemical properties of the sample under simulated circulating conditions comprises an environmental chamber having therein a plurality of motorized roller members which rotatably support a cylindrical enclosure containing a fluid sample. A heating element disposed beneath the rollers heats the chamber to a predetermined temperature which is maintained by a thermostat. An instrumentation and control panel disposed atop the chamber contains a digital thermometer display which eliminates the need to open the oven to check the temperature. A timer contained within the instrumentation and control panel may be preset to start and end the test automatically without having an operator in constant attendance.