The current mopar thermostat has a little wobble valve in it, coolant forces it closed but air can escape
I always buy dealer t-stat for this reason. If I am forced to buy a parts store t-stat then I drill a hole as mentioned above. Perhaps wrap your exhaust manifold with wrap to keep some heat out.
Four jeeps In counting I’ve yet to hold 210+ temps for more than a moment and I am using stock spec cooling system.
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