Synthetic blend is more than just a marketing hype, this is according to American Petroleum Institute engineers. While it is true that what constitutes a synthetic blend varies greatly, the reputable manufacturers use it as a deposit resistance, temperature resistance, and film strength enhancement. Amsoil would have you believe that everyone who markets a synthetic blend is not being truthful. Some aren't but most are. Stick with the well know brand names like Castrol, Valvoline, and Conoco (Motorcraft) for synthetic blends.
Use full synthetic if you have a lower mileage car or one that has used synthetic since it was relatively new. Many higher mileage cars when switched to full synthetic will leak past the seals. The synthetic is so slippery it will go right past the seals. The synthetic blends will usually not do this, and work great in higher mileage cars that are being switched from straight dino oil.
