Do Motorcraft synthetic blend and full synthetic have similar additive packs (only in different porportions)? Is it o.k. to mix the two? Was discussing this with a co-worker today. Last oil change, I used two quarts MC 5W/30 full synthetic and three quarts of MC 5W/20 synthetic blend bulk. I understand that different brands use different additives that can clash. I was figuring that since both are Motorcraft, I should be safe.