Getting straight information on motor oils is nearly impossible and now appears it will be even more confusing for us consumers. Castrol Syntec is a petroleum based oil that is produced by a severe hydrocracking process which involves heating in the presence of hydrogen and several catalysts. The idea is to convert most of the undesirable components (things that can oxidize or break down) in a refined feedstock either to lubricants or to harmless molecules. Refined mineral oils can contain as much as 20% of their volume as undesirable aromatic compounds, etc. Hydrocracking gets rid of most of this stuff and also reduces the oxidizable groups in the oil molecules themselves. This is supposed to give a product that is 99+% pure lubricant, with viscosity properties, oxidation resistance, pour points, and flash points similar to full synthetic oils. True synthetics (Amsoil, Mobil 1, Delvac 1), in principle, get to the same product by making the base stock directly from chemical building blocks called polyalphaolephins. Castrol has argued successfully vs Mobil that since the end products are essentially the same, they should be able to call their oil synthetic. As the Amsoil men will tell you, there are significant theoretical advantages to true synthetics. Since the synthetic process can be carefully controlled, there should be fewer undesirable byproducts in the oil. Plus, the size and composition of the lubricating molecules should be more uniform that which can be economically produced from crude petroleum. But it remains to be seen whether or not hydrocracked products are as good as true synthetics. Only long term on the road data, if anyone every makes it available in any form other than testimonials, will let us make informed decisions.
By the way, Castrol Syntec is an automotive oil. It is not CH-4 rated for use in low emission diesels. A good diesel oil requires properties beyond those needed by an automotive oil. Interestingly, Chevron Delo 400 is supposed to be a hydocracked product yet it does not command the premium price of Syntec. Delo does seem to be superior to other petroleum based oils according to data on the Amsoil web pages.
Sorry for the long post, but I try to keep abreast of the petroleum industry searching for the “best” lubricants. But with an engine designed to last 400,000 miles with ordinary maintenance, I am probably wasting my time obsessing about such things.
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1999 Quad cab 2500, SB, SLT, 4X4, 5-speed, 3. 54, tow and camper package, Lance 820 camper, Lance cabover stabilizers, Rancho 9000s, Airlift airbags