Once I get past 1/2 tank the needle on my fuel gauge starts to intermitently jump from 1/4 tank back up to 1/2 tank.

Also: my coolant light came on yesterday, so I check the coolant. It was a bit low so I put some water in. The light is still on. Temp seems to be just a bit higher than before. Is this a sensor malfunction?

Any thoughts/insights?