We generally don't recommend past 6,000 miles for the dexos blend simply due to the quality of the oil.
This is what sets apart oil quality pretty strongly; the time interval. The reason for the 3 month part is that the oil oxidizes. The reason why they blast the vaporized hydrocarbons in the hydrocracking process is so the positive polarity of the remaining molecules once the contaminants are removed will not react with the negative polarity of the oxygen in the air and cause it to sludge up. A hydrocracked synthetic will generally be guaranteed for 6 months, and a true synthetic will be guaranteed for 12 months.
Hey, I'm not going to argue with a chemist lol. I am certainly no chemist, and seeing as you are one, it is probably me who could learn from you. What I do know is based on the research and reading I have done, so I fully acknowledge that some of my information can be either wrong, partially correct, or incomplete. I have no problem with that.I'm not disagreeing with anything else you've said (especially all the bit about volatility which is very good info), but defining hydrocracking as purifying is not correct. Hydrocracking is breaking apart the molecules from the feedstock into smaller ones. This is a chemical reaction, not a purification which is a physical process. This is why group 3 oils are labelled synthetic.
Also, you say nothing that you purify from the ground will take the form of a plastic, but that's exactly what plastics are (except again, not purified). They are made (again chemically) from crude oil via polymerization reactions. These plastics (in this case PAOs) are then chemically reacted into the group 4 synthetics. As I said in my earlier post, there is far more chemistry (synthesis) involved in making the group 4/5 synthetics vs the group 3. Perhaps a better or clearer way to say it is that group 3 oils are synthesized DIRECTLY from crude oil (and may contain some unchanged molecules from the crude, I'm assuming there are limits here as to what can be labeled synthetic), whereas groups 4/5 are synthesized from crude oil derivatives (at least 2 steps). In groups 4/5, I'm assuming none of the molecules are in the same state as they were in the crude (for this you used the term "truly synthetic").
If we ever run out of crude oil from the ground, there will be no plastics or synthetic oils as we know them today as our raw material is gone in all cases.
I'm really not trying to be argumentative as I agree with everything you've said. It's just the chemistry teacher in me being particular about the terminology used to explain it.
I had believed that the sole purpose of hydrocracking was to remove contaminants that are otherwise impossible to remove through the standard refining process.
What is true is that in every test I have seen performed, the group 3 base stocks were inferior, all things kept equal. From what I have seen, the PAO/Ester blends will also maintain viscosity far better. They will thin a lot less in extreme hot temperatures and thicken a lot less in extreme cold temperatures. As a result, they will not require high levels of pour point depressants and viscosity index additives that will deplete over time. In fact, (I still have to verify this), it would appear that the AMSOIL signature series synthetics don't require those additives at all.
Molecular uniformity is a big selling point for true synthetics.
It is that complex. We've had people join complaining that they have to change their oil in 4,000 miles. We later come to find out that they had a 2.5 mile drive to work every day.
