This discussion comes up regularly, and it's easy to understand why. Seems every manufacturer now wants to have their own proprietary coolant blend, color, etc. Jeep has it's multi-colored range of HOAT & OAT coolants, Ford went from gold HOAT up to 2011 to an orange (Dexcool essentially) to now a "yellow" (looks green when you pour it) that is "backwards compatible" and supposed to replace the orange stuff on 2012 up models due to some issue with their version of Dexcool. I had the coolant changed on my F150 per the recommended change interval and it now sports the yellow stuff.
It's understandable consumers say "screw it" and just get the green stuff grandpa used in the 'ol CJ, but that's not a wise move. This is pretty nuts and really frustrating because the manufacturers, like Ford has done, can change their minds after assessing warranty data.
Beyond what's recommended in the Jeep owner's manual, there's a wealth of "what to use & why" information on the web. The simple "why" explanation is that unlike grandpa's CJ, a modern Jeep uses very little iron & steel in the components of the engine & cooling system. Since the demise of the 3.8L the blocks, heads, water pumps, radiator, heater core, etc. are lightweight alloys that react differently to coolants. All these components are soaked in whatever coolant is in the system for as long as 10 years, so the engineers developed coolant formulas that will be the least corrosive and reactive to the alloys & hoses, etc. The 3.8L, while still having an iron block, has aluminum heads, etc., etc. The recommended HOAT & OAT coolants are expensive, but on the other hand have extended change requirements so are pretty cost effective when you factor in the risks involved with using the green stuff grandpa used in his CJ and the potential associated repairs from using the wrong stuff.
