Most likely exhaust manifolds. The coolant passage is too small at the back and the back of the block heats up more, no fix with out a reman. Jasper takes care of this issue it seems. So the rear bolts are the first to pop due to this over heating. ( does not cause engine cooling issues, just manifold) My 2018 ticked from almost new as well, and I started attempting repairs at maybe 125K. Now after so many helical coil inserts and such I had to give up, the heads are worn out from popping bolts. My advice is to deal with it as early as you can. Part of my engines demise was just excepting the tick I think and the holes just get stretched worse over time. Its so disappointing Ram will not fix this nightmare. I believe 2019 saw an updated manifold design, but obviously not working. As for lifter failure, my experience and opinion is with oil changes they start to fail closer to 175K or so. Maybe even longer if you do not idle the motor. But the exhaust while less serious, could lead to valve problems and other issues. So far I have skated by for lots of miles, but its nerve racking. My research has discovered;
> The Coolant passage design flaw in the block is the #1 Cause
> The manifold bolts are not large enough or long enough #2 Cause
> Ram would be bankrupt if they warrantied this issue, but I am astounded at the lack of effort to address the issue. ( RAM if you fixed this for the long delayed 2025 model please jump in and let us know!)
> Regular oil changes at or before the oil life meter is critical
> Never allow a Hemi to idle for long( wish I had know that, but the dealer does not say "These 6.4s are problematic, better never let it idle" LOL
> There is an interesting header to help fix the 5.7 but not the 6.4.
I called them to see if anything was in development, and no.
I feel like Ram has a real opportunity to become a more reliable brand, and so many things have improved it seems its hard to wrap your head around. But not fixing the Hemi tick is holding them back.