Originally Posted by ChristianReske
Even in summer, a 0w-40 flows better at startup then a 10w-40, to my surely limited knowledge, according to the Kinematic Viscosity datas.
The difference in summer is very, very, small of course, but there is a difference.
Couple of points:
* what "feels like" it should be fact, and what's actually fact are often different.
* there's not really any difference in time when it;'s delivered by a positive displacement pump pushing oil into the galleries, when the oil is well within it's pumpable range (you mentioned summer, there's no difference);
* The parts are still coated and lubricated in a residual film, which is tenacious, and much thicker than operating temperature, thye are not dry, and reliant on "flow".
* Flow doesn't lubricate anything;
* The correct term is "warmup wear", it's not the instant between hitting the key and oil hitting the components, the wear is taking place while the engine warms, and with all the lubricated bits having oil. The sequence IVA, industry standard wear test, the engine is running, and fully lubricated.