There are three basic coolant types on the market today: (IAT) Inorganic Acid Technology, (OAT) Organic Acid Technology and (HOAT) Hybrid Organic Acid Technology. Your BMW, Porsche, Mercedes Benz, Audi or Volkswagen uses an HOAT coolant.HOAT coolants are derived from OAT coolants with the addition of silicate to protect aluminum surfaces. Many components of your BMW, Mercedes Benz, Porsche, Audi and Volkswagen engine and cooling systems are made of aluminum including the cylinder heads and radiators.