You need to check the color of your coolant/antifreeze....I have a 14 SRT and went to replace my thermostat with a Mishimoto 180' one. I found the same kind of brown sludge (looks just like mud) in both my over flow bottle and in the radiator under the radiator cap...now I bought this jeep brand new and mine only has about 8,000 miles on it. I found the coolant that was in my Jeep to be an Orange/pinkish color... Now my owners manual calls for only using an "OAT" formulation antifreeze in my Jeep and never mixing it with any other type...So I went to my dealer and asked him what is supposed to be in my Jeep....He checked my VIN number and agreed that my Jeep should have come with "10 year /150K mile "OAT" PURPLE antifreeze/coolant factory installed, He had me go to the service dept and they had a Service advisor look at my coolant, and he said the " OAT" coolant is colored purple, but that the Orange/Pink stuff in my car was the same and that was how it really looked....OK, So I do some internet seacrhing and find this.... In 2013 Chrysler did a change from "HOAT" antifreeze/coolant to "OAT" in all it's Vehicles.....Now I also found out that Chrysler's "HOAT" antifreeze is, READY for this?, Orange / Pink in color, and since my Jeep is a 2014 that is not what was supposed to be in it.....and that it should NEVER be mixed with "OAT" antifreeze, which is purple in color from Chrysler.... see warning in owners manual!, it also says if they ever do get mixed you must do a system flush, or damage to your system will result........ So I bought $80.00 worth (4gals 16qts) of new Mopar "OAT" 10yr/150k Purple antifreeze/coolant..... I spent about 2 hours flushing out my system, also washing out as much of this brown mud as possible, installed my new thermostat, a polished billet housing and race glass, and hopefully now all is right with the world........but I still wonder why I had this Orange coolant in my vehicle in the first place? To my knowledge no work was ever done on my Jeep that would require draining or adding antifreeze/coolant to my Jeep. I think this Brown Mud is a result of someone somewhere mixing "OAT" & "HOAT" coolants in my system....... I also read where Fiat/Chrysler did put some (ORANGE) "OAT" coolant into Dodge Darts and another model right around the time they did their"HOAT to OAT" Corprate changeover in 2013.....So I don't really know how to gauge what they put into some of our Jeeps, or if somewhere someone mixed them up.....I would suggest to anyone who is un clear of what they have, and if they are getting a mud like residue, that they flush out their systems, or get their dealer to do it under warranty, and make sure they have the Purple coolant installed........or whatever type their owners manual calls for.......note: most of the after market coolant/antifreezes that say they are universally compatable with all cars, aren't "OAT" compatable formulations......Currently, the dealership was about the only place I could find the correct "OAT" antifreeze....