Originally posted by hondatech
i think you are partly right but maybe for the wrong reasons. I let my car warm up too but only so the oil gets hotter and thinner and completely covers the internal parts before i go driving. I don't think it matters about your parts expanding and what rate that happens at. It's good that you think about these things though. The theory behind my warm up period is I want the oil that has drained to the bottom of my oil pan to get up to the cylinder head and piston rings, coat the parts before i go. thats all
I do it for that reason also, especiall ynow that i am runnin out of spec with 10w-30 (its hot, so i figured it is better, ill change back when winter comes)