If only I could get the 0W20 Pennzoil Platinum now, I could be a happ-happ-happy man!

And yet why does it make valve train noise.

Yes, 0W-30 can be thicker at operating temperature than a 10W-30. It all depends on how much VI improving polymers are added to the base 0W oil and how much less is added to the 10W oil. However, what this entire analysis ignores is the viscosity shear-down at operating temperature that occurs in all oils using VI improvers. The more improvers are used, the faster the shear-down. 0W-30 will have more VI improvers than 10W-30.

Someone on this board sent me to a dissertation on thin oils about a year ago. Thank you. However, being a dinosaur, I cannot be convinced that thinner oils provide as much metal-to-metal separation as thicker oils. Additives that "sacrifice" themselves in metal-to-metal contact are a poor substitute for keeping the moving metal parts from touching in the first place.

Why do you think they have a "high-mileage" version of multigrade oils for cars over 65K miles. The wee-wee you've been putting in your car engine has allowed more wear, and now you've got to use thicker oil just to fill in the "gaps" between the moving parts.

what people don't understand is that in the old days, visc made a big difference as far as protection. why? because it was acting like a barrier additive. it was thicker and it took more pressure to squeeze the oil out between the parts. therefore it protected more. now, we have better barrier additives and no longer have to use as thick of oil as we use to. we now get better protection in a lower visc oil but also get better gas mileage because it takes less to move the oil unlike the thick oil we use to use. visc use to play a big role in protecting an engine but now, along with visc, additives make a big difference as well.

Very good and simple explanation. I think the definition of thinner or thickens less it like 6 of one and half dozen of the other.
In case anyone wants to make their own graph, click here and supply your own viscosities: (even though it is spanish, I think you can figure out how to use it)
http://www.widman.biz/Seleccion/Viscosidad/Conversiones/Graficos/graficos.html

I'm sure pour point depresants modify the low end a little. That is a straight calculation based on viscosities input.

Bob:

Well put. For whatever reason, there seems to be a great deal of "retro-think" with respect to engines, oils, and their characteristics. Another factor that really come into play in the last decade or so is the improvement in metalworking and machining, which has allowed tighter clearances, made to very close tolerances.