The probability is that you'll never be told what is wrong with the engine. FIAT does not want that information to be broadcast around the world with social media. Be happy that they are providing you warranty replacement, and you may have to let it go at that. It would be different if you were paying for it -- then you would have all rights to know exactly what you are paying for, but since it is warranty replacement, FIAT believes that they don't need to tell you anything. I could be wrong with all of this. I'm just speaking from experience I had with engine replacement on my Fiat 500 Sport. It was one of the earliest ones built (PE #18), and the engine started making noises around 23K miles, about 6 months before the warranty expired. Fiat wanted to monitor the noise for a while, and eventually replaced the engine at 30K miles in 2015, even though the warranty had been expired by about 6 months at that time. They were very friendly, and provided me a replacement car during the waiting period, but they would never tell me the problem with the car, and believe me, I tried very hard to get the information. The main crankshaft bearings were worn, but the suspected cause or any other information was not disclosed.