Prestone or Zerex. Says "radiator cleaner" on it, check the directions on the container. Says drive for 3-6 hours, but it can be over several days.
Check the pressure bottle on the firewall. Any dampness on top of the bottle? The caps like to leak. Recommend replacing it with a Stant 10244 cap. Pros--lower profile so it isn't pounded by the hood when the bottle expands, reducing stress cracks in the bottle and damage to the cap; I screws down tighter and maintains pressure better; rated at 22 psi so it raises the boiling point of your coolant. Cons--NONE.
It is now September, so check your coolant to ensure a 50/50 mix ethylene glycol/distilled water. You should run that late September through early Spring, then when you are out of the freeze time switch over to a 30/70 mix, 30 ethylene glycol/70 distilled water. Ethylene glycol is good for two things--anti-freeze and corrosion inhibitors. It makes a lousy coolant.
When the temp goes up at idle try raising the rpm of the engine. If the temp goes back down it is a sign that the fan clutch is getting weak.