​​What is an engine flush? What does an engine flush do?

Each time your engine oil heats up, it evaporates slightly over time, in turn the oil then leaves oil deposits & sludge which constrict the flow of oil throughout your engine making your engine work harder to move the remaining oil around. You can add an engine flush is added into your engine oil just before an oil change. The flush dissolves sludge and deposits from inside the engine, then drained with the old oil, leaving much cleaner internals than left untreated.
Oil filters can be incredibly effective and can catch particles as small as 10 microns. That being said, there are still a lot of particles located in the engine’s oil stream which are smaller than this and even with a high-quality filter, these particles can’t be removed. Over time, they can build up and cause a noticeable drop in your engine’s performance. Sometimes, simply replacing an engine’s oil won’t get the job done, it is recommended that you change your filter every time you change your oil as this can ensure that your future oil remains cleaner for longer.