Is there a way to tell if it's a bad temp sensor or a bad thermostat ?? I'm leaning towards the temp sensor but I'm just not quite sure , also the coolant level was almost non existent so would that cause air pockets ? I can squeeze the top and bottom hoses and see air moving into the coolant resivo...

Hello , I have a 2000 s80 2.9 and my temperature gauge will not read at all , says its cold yet upon starting the vehicle the fan instantly kicks on , heat is still working , could it be the thermostat , and for what I'm hoping to be a completely separate problem also just changed out my cylinder 1 ...