If your gauge has never been 'fixed', the excess temperature fluid is likely symptomatic of some other problem such as a kink in the tubing or an air bubble in the line. If you inspect the line and see no kinks, often you can eliminate the air bubble by removing the gauge, straightening the line out and turning everything upside down with the bulb at the top and the gauge at the bottom. Another method, believe it or not, is to grab the line right at the gauge end and briskly swing the line in circles with the bulb at the end of the arc.
You can readily add fluid to the fuel gauge, with the trick being that it is the same liquid that is already in the gauge.