But wait, there's more!
Here's one big reason why I persist with this post - information. It is isn't the base oil that shears down and makes the oil behave thinner, it is one of the additives called a viscosity index improver. Deteriorating the base oil only leads to thickening (oxidation, nitration, loading with soot, etc.) Shear (breaking apart the VII molecule) is what leads to thinner oil.
Even the API SL category has changed US base oils, due to the volatility and engine requirements for the 5W-30 and new 5W-20. There are Group II, II+, and Group III base oils, and some Group IIIs are performing like synthetics. (See Castrol references in earlier posts.)
No question that European ACEA A1/B1 oils are higher performing (and higher additive treat rate!) than API performance level oils. But again, to put it into perspective of earlier discussions, there is a huge additive package difference besides the base oil differences. One reason is that most oils aren't only A1 (gasoline performance) but also B1 (passenger car diesel performance) so they need additive systems that can handle either. That makes for a robust oil, a more expensive oil, and now you can see the difficulty in marketing something like it in the US, where the average consumer has been trained to look for what has become basically a commodity product.
Here's a challenging question for the car company guys, Ron- why not increase the sump size? That would instantly decrease oil temperatures, extend oil drain life, reduce oil consumption worries, at little cost to the OEMs, I would think.
High oil temperatures, whether the oil can handle it or not, have collateral damage - running 300F in the oil means coolant temperatures have to be close by, so the coolant is near the boiling point (isn't it 284F or 264F with a 15lb cap?) Also, the intake charge is heated, so the engine is highly prone to knock or would get large amounts of spark retard. To be fair, there are requirements that all API oils must pass that run at 300F for the entire test.
It would be far beyond the typical consumer's understanding to to the viscosity at all temperatures, but the system we have isn't that bad. The multigrade values, the 15W and the 50 are indeed only two points, but on the correct graph paper, the dots make a straight line. Maybe what's needed if low temperatures are the issue is information about how low a temperature a 10W or a 5W is good for. Those that live in Florida and Canada can then make their choices smarter.
Steve makes an important point about additive packages- that good oils with synthetic base oils usually have a good additive package. And that's why it's harder to attribute the resulting performance to one or the other, since you get both together.
I'll have to look on a map, Steve, but here it gets down to "only" the low single digits; perhaps 0F. And sure, I notice the 15W40 makes things a little slower. Maybe you could revisit your experiences based on ambient rather than wind chill temperatures. Since engines don't have sweat glands, the wind chill only cools them to the ambient temperature quicker, but doesn't have the evaporative cooling to make them lower than ambient temperature.
Hee, hee, you had given yourself away as an Amsoil guy, so the article seemed appropriate. Yes, I also try to remain brand-less (how am I doing, anybody guess?) and so maybe I challenge what I consider to be marketing claims rather than technical claims. And I have thick skin, so whenever you think it's my opinion, point it out and I'll find the data.
Additive links? Here's a site of a past co-worker, he's got them all listed already.
Additive Company Links