Engine buildup is the process of adding components to an engine in order to improve its performance. The two crossword solutions for this term are 'GUNK' and 'GRIME'. GUNK is a thick, sticky substance that can accumulate in an engine over time, while GRIME is a layer of dirt and dust that can also build up in an engine. Both GUNK and GRIME can reduce the efficiency of an engine and should be removed during the engine buildup process.