Anti Freeze / Coolant - NOT. I always do start up and the first few hundred mile break in with just plain water with a small can of corrosion inhibiter added to it. I have consistantly noted a 10 degree rise in operating temp after the system is drained and refilled with the 50 / 50 mix of anti freeze and water. The explanation is simple. Nothing absorbs and dissipates heat faster than clean water. Aside from the obvious reason to run anti freeze it also raises the boiling point of the water proportional to the strength you mix it so it is a trade off in some respects.
