I have a 2018 and had the cam phasers done about 2 months ago and very similar condition afterwards, it would get up to 238 just passing someone on a 50 deg day.
Fordtechone noted in another thread about thermostat, as the phaser dealer didn't know....jogged my memory about removing and reinstalled thermostats not functioning fully, so I swapped my thermostat and viola, fixed!
Since I occasionally tow over mountain passes I went with an OE 180 deg thermostat....a mustang gt350 180 deg is OE temp
Fordtechone noted in another thread about thermostat, as the phaser dealer didn't know....jogged my memory about removing and reinstalled thermostats not functioning fully, so I swapped my thermostat and viola, fixed!
Since I occasionally tow over mountain passes I went with an OE 180 deg thermostat....a mustang gt350 180 deg is OE temp