Originally Posted By: Corvette Owner
This was posted on Corvette Forum by "mAydAy121"
Mobil 1 Extended Performance is a 'true' synthetic oil made up entirely of polyalphaolefins (group IV base stock) which are chemically engineering and derived from chemical reactions, versus regular Mobil 1 is made from group III base stock which is more refined 'dyno' oil. As a result of a lawsuit between Mobil and Castrol, group III base stock dyno oils can be labeled as 'synthetic' although in all honesty they are not synthetic. Buyer beware when purchasing a synthetic oil -- not all 'synthetics' are created equally, especially since most aren't synthetic....
Mobil 1 Extended Performance is very closely comparable to say Amsoil. I'm a firm believer in running Mobil 1 Extended Performance, or Amsoil, and have had great results with both. If you want to be sure everything is being protected satisfactorily, run the oil for say 5000 miles and send it off for an oil analysis to get specifics.
You are only partly right. Mobil 1 is a blend of grp 3-4-5. All Mobil 1 oils would fall into that catagory only with differing amounts of 3-4-5.
As far as OCIs go. I have used the Mobil 1 10w30 in some very high mileage engines. My sons Ranger has 334,000 miles on Mobil 1 10w30 at 10-13,000 mile OCIs. His truck still runs great.
Also last Dec. I did call Mobil tech and they told me all Mobil 1 oils are in Grp 4.