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Extended Life Coolant, otherwise known as OAT (Organic Acid Technology), NOAT (Nitrited OAT) or HOAT (Hybrid OAT)does not need Supplemental Coolant Additive. It is formulated with everything it needs for 1 million miles, 20,000 hours or 8 years of service. Here's one example: http://www.phillips66lubricants.com/documents/antifreeze_coolants/FinalChargeNOAT_50-50_TDS.pdf
If NAPA is advertising ELC and coolant with SCA as the same thing, they don't know what they're talking about and should be avoided.