The contact owns a 2018 Ford Mustang. The contact stated that while starting the vehicle, there was a misfire coming from the engine. The contact stated that the vehicle was shaking abnormally, with the check engine warning light illuminated. The vehicle was taken to an independent mechanic, where it was diagnosed and determined that the head gasket had failed, and the engine needed to be replaced. The vehicle was not repaired. The dealer was contacted. The vehicle was not diagnosed or repaired. The manufacturer was made aware of the failure. The failure mileage was approximately 66,637.