A process for thermally cracking waste motor oil into a diesel fuel product is provided. The thermal cracking process uses low temperature cracking temperatures from 625.degree. F. to 725.degree. F. with ambient pressure to generate a column distilled fraction of diesel fuel mixed with light ends, the light ends being flashed off to produce a high quality #2 diesel fuel. The process further provides for removal from the cracking vessel an additional product stream which, when filtered, is suitable for use as a #3 fuel oil and that can be further blended with a bunker oil to yield a #5 fuel product.