An apparatus for testing engine oils and in particular oils to be used in compression ignition engines. The apparatus includes a receptacle in which a sample of the liquid oil to be tested is poured. The receptacle has a cover plate with an opening. A test plate is mounted in the opening of the cover plate and seals the receptacle. A shaft with radial projections is mounted in the receptacle and submerged in the liquid oil to be tested. When the shaft rotates the projections splash oil against the test plate. First temperature sensing means are mounted in the test plate and second temperature sensing means are submerged in the liquid oil. A heating element is mounted over the cover plate. The first temperature sensing means are operatively connected to the heating element via a thermal regulator to thereby maintain the test plate at a preselected temperature. The second temperature sensing means serve to maintain the liquid oil sample at a preselected temperature.