Water temp sensor and coolant sensor issue

[zerolux]

g'day y'all

hope someone can help...the gu (tb45e) got cooked by the missus who swears the temp never got above half, which looks like from the reading that that may be a common issue, but the parts book says there is a coolant sensor as well as the temp sensor, do the gu's (mines a 2000) have the coolant level warning light, as i cant say i've seen one, and what does the coolant sensor do then??

Thanks for any advice
Jarrod