I agree, should not affect ECT. Provided it allowing proper flow of coolant in and out of reservoir. But recheck level under cap periodically, after 8 hour cool down, with heaters set to hot the drive before cool down. The check needs to be when cool OAT in the morning out of the sun, and with front higher than rear of vehicle, to get best results.
What I have found with non OEM caps. They do not fit as tight. That when I pressurizing system for test or to blow out during a flush, with ~10PSI into rad through reservoir hose. I'll see and hear leakage out of non OEM caps.
Once coolant system to spec. Which includes the foam arounds side and top of radiator (lower foam seems to have less effect). Tune engine and make sure no vacuum leaks and PCV valve working. Also run a fuel system cleaner through the gas. I like 44k and or Chevron Techron (at different times). I also have been using IK20TT denso spark plugs. Don't have any comparison to non TT, but may drop cylinder head temp a tad, but IDK.
Watch fuel trims too see if running lean.
I just learned from
@abuck99. That the coil on front of fan clutch, even new OEM. Are reportedly varying from one to another.