Abstract: A test apparatus includes a test chamber adapted to support a test piece having the shape characteristic of an engine intake valve. Means are provided for heating the test piece, delivering a selected test fuel to the test chamber at a controlled rate and at selected intervals, and for delivering a flow of heated air through the test chamber at a preselected temperature and volumetric rate. A method for determining the relative ability of a fuel to form deposits on an engine intake valve includes placing a test piece having the shape characteristics of an engine intake valve in a test chamber, heating and maintaining the test piece at a predetermined temperature, passing a stream of heated air through the test chamber at a controlled temperature and flow rate, and alternately repeatably spraying a sample fuel onto the test piece and drying the test piece, for a period of time sufficient to establish the deposit-forming characteristics of the sample fuel.