Needs some input on coolant system  coolers, drops temps and lubes. 

A good additive is Water Wetter.  Supposedly it works best with straight water, but will mix with glycol easily.  Coolants have anti-corrosion and lubricants blended in which are needed anyway.  The Water Wetter treats the metals of the cooling system and coats them to enhance heat transfer. 

There's also a product called 40 Below, which is more expensive, but I have no idea if it's any better than Water Wetter.

Before you do anything, no improvement or product can help if you don't make sure your cooling system and its components are clean and in proper operating condition and the seals are in place around the radiator.