The Ford Mustang GT manual states that the you should change your synthetic oil roughly every 10,000 miles in "normal" driving conditions, and sooner if under extreme driving conditions. Many Mustang GTs have a Intelligent Oil Life Monitor installed that will inform the driver when the should and need to have their oil changed.
Ford recommends that if your Mustang GT does not have an Oil Life Monitor, or if the monitor is faulty, you should have your synthetic oil changed every 5,000 miles or six months, whichever comes first. This will help prevent potential and engine damage and failure, as well as excessive wear.
Most synthetic oils are rated at or above 10,000 miles, meaning that an oil change ever 5,000 miles is a little excessive. While it may be excessive, however, changing your Mustang GT's synthetic oil every 5,000 miles or six months is very preventive, and can potentially help your engine last longer.
