What year + how many miles?
Are all the hoses original?
Caution-
Any shortage of coolant could cause a false indication to the fan sensor, temp guage, thermostat, and cause more over heating.
When you lose your max heat, cut her down.
1) Do a coolant pressure test done ASAP!
2) Replace any bad rubber hoses, or clamps.
3) Try blue devil, metallic blockseal, or
http://www.steelseal.com ,so you don't have to chase coolant problems.