Took Mustang Ecoboost to Ford dealership as result of steady check engine light. Prior to check engine light rough idle at start up that smooths out after 10 to 15 seconds. Dealer identified CYL 3 misfire as well as random misfires. They also observed carbon tracking on plugs. Dealer replaced plugs and performed GDI cleaning service. About three weeks following repair same conditions reappeared rough idle and check engine light. Upon dealer inspection and use of bore scope discovered coolant intrusion in cylinder and recommended long block engine replacement. The second dealer appointment was several days after my warranty expired and mileage was 30,106 miles. Although the dealership was very supportive and understanding Ford would not provide any assistance even after I also pursued relief directly. As a result the long block engine replacement cost is $8,200. After considerable research was able to identify that ecoboost 2.3 engines as well as other small ecoboost engines all had a block defect that has since been corrected. The defect tends to permit, over time, coolant to leak into cylinders. Although a new head gasket may correct the condition, Ford normally recommends long block engine replacement as a long term fix. This condition if not attended to or if coming on suddenly will cause total engine failure. And, as failure can only occur when operating an engine failure under any driving condition is fraught with danger. To my knowledge Ford has not taken any steps to address this issue with the 2.3 liter engine built prior to about February 2020. And, at that time made an engineering change to the engine block addressing the design defect. Additionally, Ford did provide relief to owners of other smaller ecoboost engines having a similar design defect. At the present time there are several class actions suits pending for this 2.3 coolant intrusion issue. One final point should an ecoboost experience CYL or random misfires ensure bore scope is employed.