Royal Purple is 10 times more oxidation stable in this test. Unless oil is contaminated, oxidation is the sole measure of oil life. Energy savings alone can exceed the cost of the oil. It protects during operation and acts as a preservative oil during shut-down. New machined bearing surface appears smooth until magnified 1500 times.
Surface is much smoother than new surface.
Some interesting information on Duralube and Prolong for the layperson. We now accept Visa and Mastercard over the phone.