It is widely known that all Synthetic oils have a molecular structure that is much smaller than conventional oils and therefore synthetic oils must use seal swelling additives in order to stop the oil from leaking out. Is this so?NO! Synthetic oils are unique that there structure is more uniform then petroleum oils not smaller. In Petroleum oils the molecules are larger and not as even in size as synthetic oils. Just because synthetic oils have more uniform molecules in size, has nothing to do with seal failure or oil leaks. For example, the Olefins in Mobil 1 tend to cause seal shrinkage and seal swelling additives are used to counteract this tendency of like group IV synthetics. However ester based lubricants group V’s (example: Neo)tend to cause seals to expand, and the need for seal swelling agents is totally unnecessary.
