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Hi harryd, There are times when engine flush can help, such as when there are visible deposits of sludge, but after treatment, the cause of the sludge formation must be found and corrected. The problem with engine flush additives is that it thins out the oil, and some of it remains behind in the engine, where it thins out the new oil as well. Another problem is that sometimes, the engine flush does not fully dissolve all the sludge. In some cases, it only loosens the sludge, or breaks it up into smaller pieces that can block the oil pick-up, starving the engine of lubrication, so yes, it can destroy your engine. Sludge can never be good for any engine, no matter how little there is of it, and you are right in saying that regular oil changes is the best way to keep an engine clean. Stick to one brand of oil, and it should never be neccessary to use any sort of engine flush, and certainly not after 80 000 kms. The service adviser is just trying to make some extra money, so don't let him put engine flush into your engine unless there is a very good reason for it. Remember though that using different brands of oil can cause serious sludge formation, because of the fact that the additives used in different oil formulations are often not compatible. When additives are not compatible, they cancel each other out, which means that the detergents that should keep the engine clean, stop working. It can also happen with additives that are designed to reduce friction. If these additives cancel each other out mechanical wear is increased, resulting in premature engine failure. The engine flush guys are wrong when they say that oil filters cannot filter out particles smaller than 25 microns. Good quality oil filters can filter out particles as small as 5 microns (and sometimes smaller), but it depends on the type of filter media. Filters that use paper don't work as well as filters that use polyester wool, but in all cases, a good quality filter should catch anything between 5 and 7 microns in size. Some cheap Chinese oil filters let through particles as big as 30-40 microns, so avoid cheap filters like the plague.