The Paratherm AP (antioxidant protection) additive is designed to be added to operating hot-oil systems to extend the oil’s useful life. Incorporating a sacrificial antioxidant, Paratherm AP prevents the acids that form during heating the oil from converting to sludge. The company notes that the AP is not a permanent cure — sacrificial additives become depleted over time and eventually the protection stops. So antioxidants don’t eliminate the need for preventive maintenance, they just reduce or delay the need for oil change-out. Periodic testing is the only truly accurate way to tell whether the additive is still present. Paratherm AP additive is available in 55-gallon drums.