Can an Engine Oil Flush Damage the Engine?
An engine oil flush should never be necessary unless certain circumstances exist. Performing an engine oil flush could dislodge and send harmful particulates into small passageways and clog the engine. Additionally, the flushing material could cause leaks in places where none existed before. However, a flush may be needed if a foreign fluid was added to the crankcase. An example would be transmission fluid, power brake fluid, power steering fluid, or engine coolant. Any of these fluids could pose danger to the engine, and merely draining the oil may not completely remove them from the engine.
For more info, see How to Tell If You Need an Engine Flush