There are several fluid changes that need to be performed every so often over the life of a vehicle. Usually, these include transmission fluid flushes/exchanges, power steering fluid flushes, brake fluid flushes, and coolant flushes. Fuel injection cleanings also fall into this category.
Service Intervals
The recommended intervals for these service changes vary from manufacturer to manufacturer, so it's best to consult the manufacturer's recommended maintenance guide. Certain fluids need to be changed more often than others--for example, transmission fluid needs to be changed the most often on most car models.