Coolant or antifreeze: Green or pink-colored liquid specifically designed to be used inside of the engine as a refrigerant.
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They are glycol-based liquids, which gives them anti-freezing properties. They have additives that stop corrosion and do not settle in the internal parts of the engine. They also elevate the boiling point and stop foam from forming.
Oil is getting in to the coolant.It is not sludgy looking.It is black floating on the coolant Expansion tank cap is also oily Could it be the oil cooler causing this The car is not over heating