OP, to rule out the possible inaccuracies use patches of electrical or masking tape on the spots you measure with the IR thermometer like Sugar Bear advised.

Also,you can check the proper function of the temp sender (measure on sender post and vehicle ground) :

https://www.peachparts.com/shopforum/attachments/diesel-discussion/156494d1585344039-foglights-coolant-gauge-not-working-resistance-values-vdo.jpg