A proposed test procedure, Sequence IIIC, has been developed to evaluate the thickening characteristics of engine oils. Results from the new 64 hr test procedure correlate well with the oxidative oil thickening observed in service vehicles and test cars. Sequence IIIC also evaluates the sludge and varnish tendencies as well as the wear protection provided by an engine oil. Sequence IIIC is intended to eventually replace the 58 hr Sequence IIIB test. Only minor changes in engine components and auxiliary equipment are required to convert a test installation from Sequences IIB-IIIB to Sequences IIB or IIIC.