Help diagnose
 

I have a 2000 grand cherokee limited with 4.7 v8. Only 123000km. The last few days my low coolant comes on but rad is full to the top. Over flow bottle was a little low. Added coolant but light is still on. Checked oil level and it is high. Not due for a change for 1 month and 2500km. No signs of leaks. What can I do to check for possible head gasket leak?

the sensor in the over flo bottle is getting stuck or crapping out un plug it light should go out,replace or live with it