What one needs to remember regarding additives in motor oil is, if you are using a Multi-Grade motor oil (which most of us use nowadays), the oil already has a polymeric additive typically referred to as a Viscosity Index Improver (VII). These help sustain the viscosity of the oil over the typical temperature range the oil would experience. There really is no need to add another oil additive to these motor oils. Single-Grade motor oils could possibly benefit from an oil additive, but typically these grades were used in older model engines & oil change intervals were recommended by OEMs as being between 3000 & 5000 miles. It would be unusual for these oils to degrade enough to require a "boost" from an oil additive as long as the recommended oil change interval was being adhered to. And over the years, there have been significant improvements in engine design and motor oil formulation (my 1968 Mustang Fastback didn't have synthetic motor oil available to use) such that today's OEM recommendations typically don't reference additional oil additives. Like others before me, I don't add any additional oil products to the engines in my cars.