2012 says 5-30. Later years say 5-20. Maybe somebody knows the real answer, but I don't think we here on these forums understand. Some say due to head issue. However, Chrysler also never really defined what the head issue was, so how do we know if the oil was meant to address it? Other think, and I tend to agree that the primary reason was to get a fraction of improvement in the MPG's. I certainly would ask your dealer to tell you why they put in different weight than what is specified for your jeep. However, take that with a grain of salt because some service managers are idiots.

 

My service manager is a straight shooter. When we discussed this he didn't know the real answer. According to him Chrysler never has told them what conditions cause the head to fail. They just told them to replace them as needed. They also haven't had an answer as to why the oil grade changed with no major changes to the engine. He said that usually will get a notice to change the grade of oil on all vehicles with the same motor but in the case of the 2012 JK they are told to just go with what the original spec is.
I have noticed the sound at start up is different with the different oils I have used. I have been thinking of sending some oil in for analysis with different brands and 0W-30 vs 0W-20 vs 5W-30. If I run each for 500-1000 miles It would be a long and costly venture but is the only way to know for sure which oil is best for the motor.