Q: How often should the entire engine be flushed?
A: If the engine has been properly maintained (oil changed as recommended by the manufacturer) then an engine flush should not be necessary. Take off the oil filler cap and see if sludge is built up in the underside of the cap. If there is a build up of sludge in the engine, then you may want to flush it. Some service centers have special machines, or if you do decide to flush it yourself there are products you can purchase at your local parts store.