The Sequence IIB rust test procedure did not provide sufficient differentiation among better quality SE engine oils. A new, more severe test, Sequence IIC, was developed to provide the improved differentiation. In general, Sequence IIC results are about one-half rust rating number lower than Sequence IIB results on minimum quality SE engine oils.Sequence IIC results correlate very well with short-trip car data obtained with either leaded or unleaded gasoline. The location and amount of rust and/or discoloration observed on lifters from short-trip car tests, conducted with either leaded or unleaded gasoline, are reproduced in Sequence IIC tests using leaded gasoline. In addition, the procedure has sufficient sensitivity to show performance changes with relatively small changes in additive concentration.Since the precision of the Sequence IIC procedure approaches that of the CRC rust rating method, improved rust rating techniques must be developed if the precision of the procedure is to be significantly improved.