Abstract: A method for manufacturing antifreeze comprising manufacturing biodiesel; collecting the byproduct glycerin of such biodiesel manufacture; adding water to such glycerin to generate at least one mixture of glycerin and water; adding at least one anticorrosive additive to such at least one mixture of glycerin and water to generate at least one antifreeze; and placing such at least one antifreeze into at least one automotive cooling system. The antifreeze viscosity is adapted to be within the viscosity range between propylene-glycol-based antifreeze and ethylene-glycol-based antifreeze. Also disclosed are “blended” biodiesel-derived glycerin/ethylene glycol coolant/antifreeze products and biodiesel-derived glycerin/propylene glycol coolant/antifreeze products. Marketing methods are also disclosed, along with material compositions.