In Mustang Times Vol.25 No.8 Art Hyde answers a readers question about using synthetic oils in his new Cobra. Art Hyde's response: "Synthetic oils can be introduced into the engine new, but more conveniently at the time of the first normal oil change. To maintain warranty coverage, the synthetic oil used must meet the Ford SL/GF3 5W30 oil grade and viscosity recommendation.
Additionally, we still recommend you change your oil every 5,000 miles (3,000 miles severe duty). Our evalution of synthetics shows a concern with compatibility to silicone-based seals/gaskets at high time in service. Since there are many various synthetic formulations on the market, it is difficult to give an overall general endorsement of synthetics or any particular brand. Ford Motorcraft oils are highly developed and tested, and provide the best overall lubrication performance for Ford engines. The high cost and limited benefits of synthetics prevents us from using them in produciton."