[JFP in PA]

Not quite correct. Yes, going to 10W-40 oil (specifically Castrol’s new version of Syntec) does raise the low temp viscosity while maintaining the higher temp vis, but experience, and several hundred used oil analysis, have shown that:

1. While a 40 weight hot viscosity is plenty for the poster’s ambient temperatures, Mobil 1 0W-40 shears down to very thin viscosities, often in less the 2K miles of use at even moderate conditions. So what started out as a 40 weight hot viscosity ends up being more like 20.
2. Oils with more than 25-30 points spread between their low temp and high temp viscosities tend to shear down significantly faster than oils with 30 or fewer points spread, and then tend not to recover. This requires more frequent oil changes in order to provide any protection in the heat. Unfortunately, none of the oil companies talk about this.
3. Brands do matter. UoA’s have consistently shown some companies invest far more in their marketing than they do in their products.
4. Ratings matter. Ever since the API moved from being the technology and specifications “gatekeeper” to being the public relations and lobbying arm of big oil, manufacture’s are allowed to in-house test and certify the ratings their own products, and we totally ignore their ratings system. ACEA on the other hand requires that oil vendors become signatories to a technical concord agreement, and then submit only finished products to independent lab testing in order to receive ratings. Unlike API, who allows substitution of components without retesting, ACEA requires much more stringent testing and resubmission if anything in the formulation is changed. This is the reason that several Mobil 1 products totally lost their ACEA ratings; they were reformulated, and not for the better.
5. Several companies seem to outright lie about their products, assuming you are dumb enough not to notice. More than one “marketer” of so-called high performance oils imply that their products “meet ACEA requirements”, or “are approved for ACEA applications”. However, a quick check with ACEA shows that these companies are not signatories of the testing concord agreement, and therefore could not even submit their products for testing, even if they wanted to. A couple of these firms (names you would recognize) have been called out in public on these issues, only to then state “ACEA specs are very expensive to acquire and are not particularly meaningful in the markets they serve.” Yet they continue to use deceptive marketing practices designed to make you think they hold ACEA to sell what testing shows to be inferior products.

If you thought that email from some guy in Nigeria about the fortune you just inherited raised the “caveat emptor” hairs on the back of your neck, you should look into motor oils more closely……….