Tune up is a term used to describe the process of adjusting and warming up an engine or other mechanical device. The crossword solutions for this term are ADJUST (6 letters) and WARM (4 letters). Adjusting an engine involves making small changes to its components in order to improve its performance, while warming it up involves running the engine at low speeds until it reaches its optimal temperature. Together, these two processes help ensure that the engine is running at its best.