Even though it is relatively new I'd start by replacing the thermostat with a Behr, Wahler or a genuine MBZ. I've seen new thermostats which were defective right out of the box.

Also clean, tighten and examine the connection at the sending unit.

When checking temps with the IR, put a piece of electrical tape on the aluminum housings and aim at the tape.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer