Ken-you forgot to post the other link about how Group III's got to be called Synthetic.
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trey-His Pennzoil is a Group III oil that takes Petroleum products and "rearranges" the molecules to form a much more stable oil-the molecular structures are much more uniform than conventional oil.. It is a cheaper process and yet they charge as much as Mobil 1. Mobil I is a Group IV (PAO-Polyalphaolefin) it is made by starting with a gas (ethylene) and the uniform molecules are "knit" together to form perfectly uniform molecules optimized for lubrication. They are more uniform than the Group III. The PAO can withstand more abuse without "breaking down" than a group III. It is better able to withstand lower temperatures than the Group III. Additives make the Group III "almost" as good as the PAO but not as good. The Group III in general can't go extended drain intervals as well as Group IV.
The big problem is: You are paying just as much for a cheaper product. But Pennzoil is happy because their product margin is much better.
To answer the question about your dad: This is not a slam on him- Many folks are reluctant to change their opinions once they have gone to the trouble of reaching them. Ask him to read this board- I'm guessing he won't. You have your answer on your dad. He is not interested in changing his mind.
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Don't waste your time trying. I have tried unsuccessfully for years trying to get other folks to switch oils. I came to my senses and gave up
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