The lifter problem was primarily with the 2012 and early 2013 engines. The lifter bearings would fail prematurely and start to wear the cam lobes. If left long enough, metal filings will migrate to the cam bearing surfaces (which can only be repaired by replacing the head) and the engine block (necessitating an engine overhaul).
Lifter bearing failure can occur in newer 3.6 engine, but isn’t as prevalent. When a lifter bearing does go bad, there will be a ticking noise. If caught soon enough (before the cam is damaged), it can be repaired by replacing the lifters and push rods.
Using the specialty tools, which are inexpensive and can be ordered on Amazon, replacing the lifters and push rods is a straight forward job, once you have the upper and lower intakes off. If you have a shop do the work, your wallet will take a hard hit!
The oil cooler/filter housing is made of plastic and is known to fail. Dorman makes an aluminum replacement that’s supposed to be a fix (I have no first hand experience with it) and is about $300, give or take. I haven’t had a problem with the oil cooler yet.
I have a 2012 Rubicon I bought a year ago with 122,000 miles on it and have put 20,000 miles on it since. In that time, I’ve replaced the thermostat, oil pressure sensor and clutch. I need to replace the belt tensioner, belt and the power steering pump is going bad. Other than that, the engine has been trouble free.
My 3.6 doesn’t use much oil, but the engine is sensitive about oil level and oil changes. Keep the fluids topped off and keep the air filter clean. Cold air intakes are a waste of money. Keep the battery terminals clean and tight.
The 3.6 loves to rev!