Originally Posted By: Raven
If I think about it, it's actually not to hard to figure out the oil weight is not correct.
Let's say 0W oil at 20 deg C has a viscosity of 40 cSt, and maintains an idle oil pressure of 2.8 bar. (Making up numbers here. Conversational purposes only.) When you pump that through the engine, and if you have an oil pressure sensor sensitive enough, you can tell based on the pressure at that oil temperature if it's lower or higher than a certain range. Whereas if someone stuck 10W oil in it, and at that same temperature, it might have a viscosity of 90, and thus an idle oil pressure of 4.8 bar, you'd know something is amiss.
Still curious about the matter: I'll have to poke around to see what this rumor comes from.
My opinion is that the value of that information, compared to the cost of determining that information, is minimal to non-existent. Lots of cars and trucks are sold in the North such as Canada and Alaska, and also in the South such as Mexico or even Saudi Arabia. I do not know this as a fact, but it would not surprise me that a Chevy Suburban sold in Saudi Arabia has a different oil spec than the same truck destined for Canada.