There are plenty of synonyms to the term "running good" that one can use to express the idea of something being in good working condition or functioning well. Some of the most commonly used synonyms for this term include running smoothly, operating perfectly, functioning flawlessly, working efficiently, operating with ease, running well, functioning optimally, operating at peak performance, and operating at an optimal level. These terms can be used interchangeably and can help to add variety to writing or speech that relates to the idea of something running or functioning well. No matter which word one chooses to use, the message remains the same, something is running or working well.