Red Line Water Wetter contains a surfactant in it which breaks down the surface tension. This creates a better union between the coolant and the water jacket which tends to increase heat transfer between the two.
If the radiator is large enuf, this will allow the additional heat to be removed before recirculation.
The downside, from my experience with this particular product comes when using it with straight water as it does not seem to have enuf lubricant in it to prevent rust after six months or so.
I like RMI-25 better which has some other attributes as well as extra lube.
