Hey Tom.... I have a somewhat on topic question. I was recently told that ALL 5W20 oil (the current recommended weight for most new Fords) is semi-synthetic. Is this accurate, and could you please explain to me the reason for this recommendation? Some of the engines are the same ones produced when 5W30 and 10W30 were recommended (i.e. the Triton V8 series). Just want to know the "why" in all of this.... Thanks in advance.
I don't know how anyone, even in the industry, would know that. It would take many chemists many hours and many tests, and then it would still be complicated by the additives in the oil that make the lab tests extremely complicated to interpret when looking for the base oil types.
When formulating an oil, you start with with the base oil needed for the low temperatures (the SAE 5W) and later include additives (viscosity index improvers) make it behave like a thick oil at higher temperatures. To get the precise starting base oil, it is usually a combination of one base oil that is a little higher and another that is a little lower in viscosity. (Refineries only make base oils in certain viscosity grades so they can sell throughout the industry.) The lower one tends to be more volatile (evaporates) and the higher one tends to hurt low temperature performance. The mix is therefore a best combination of a low volatility and low viscosity base oil (probably synthetic or Group III) and one that is simply a "pretty good" base oil (Group III or Group II+). The cost-performance trade off becomes pretty scary when planning on millions of gallons of product. So the comment really extends to any oil, not just the 5W-20.
However, the 5W-20 (it used to be the 5W-30) is right on the edge of dramatically becoming a very expensive product to make depending on the final formulation. Besides the base oil issues, the car companies have thrown extra requirements on the 5W-20 that aren't needed on higher viscosity grades. In the end, I suspect the comment is aimed at the difference between Group III and "true" synthetic, since there is still a division about whether Group III should be called synthetic or not. It's doubtful that a 5W-20 could be formulated with any significant amount of "pretty good, regular" mineral oil. The marketing problem is that some people, both technical and not, consider Group III base oils as "synthetic" (i.e. Castrol, Shell...) and some people do not (Mobil.) Therefore you have to ask the person giving this opinion what they really meant.
The SAE 5W-20 provides cold weather flowability of an SAE 5W; no big surprise there. Ford and the other OEMs have succeeded in making rounds parts more perfectly round and flat parts more perfectly flat, such that a thick oil film is no longer needed to keep moving parts separated by a thin film of oil. Nothing really surprising there, either. The benefit is that the oil pumps like an SAE 20 instead of an SAE 30 or 40, so the work is less, the effect of splashing around in the oil pan is less windage on the crankshaft, etc, etc. It's for fuel economy. There is no other inherent benefit of an SAE 5W-20 over a 5W-30 or 5W-40 or 5W-50 other than fuel economy.
