Originally posted by kowached
Only Amsoil, Quaker State, Pennzoil, and Vavoline, plus a few others are truly "synthetic". Mobil 1 & Castrol Syntec use Group III hydrocracked base stock (utra-refined mineral oil) in their "synthetic" oil, which is good stuff, but not truly synthetic.
Unfortunately, that is only true for Castrol Syntec. Syntec is NOT a Synthetic PAO/Ester based oil, it is a Group-III mineral oil "chemically pseudo-synthetised" hydrocracking to convert wax impurities (very undesired re sludge) into longer-chained oils without loss of volume thereby maximising profit per raw barrel of material. Owners of Audi, BMW, Porsche & Mazdas have reported black gloops of wax deposits coming out during oil drains which are not good for drain-pan screens or HLAs. Ash content is 1.2%, higher than any of the PAO/Ester based synthetics (<0.5%) and higher even than plain Castrol GTX at 0.7%. Ash forms deposits on valves and sludge, as HLAs will indicate. There are better oils on the market than this, for the same price or cheaper. Unfortunately Mobil taking Castrol to an advertising tribunal merely had the effect of allowing just about anything to be classed as "synthetic" when it's not a Group-IV/V PAO/Ester base. Hope this helps to clarify things a little better.