Temperature/ Coolant/ sensor/ fan question

[Cro]

Question for the more knowledgable, my coolant temp needle while driving sits at 1/4, sitting at lights or slow driving it will go to half way and today for the first time parked with the engine running the needle shot up to full and had the engine light one.

Whats likely to be the problem, thermostat, or sensor? or both?

 

[DannyR]

No water in cooling system!?

 

[PMac]

This happened to me on Saturday. I have a leak :dapprove:

 

[beij]

mine was doing this changed the sensor and it still did it ended up being the thermostat!!!