What model is it, TA or other? Do you have the plastic baffle strip under the radiator support that also directs air from under car, or front air dam?
What radiator is in it, do you know the age or condition of it?
Coolant sensors are cheap, easy to swap it it to confirm same reading and to use a infra-red temp gun to confirm if gauge reading is fairly accurate too.
Do you know the age or type of water pump?