Gotta disagree with the above advice- - - -multi-weight oils don't change thickness according to temperature, they just lubricate like a heavier-weight oil as they heat up. The physical thickness stays at the lowest rating, which does not do a good job of cushioning parts with wide clearances. Try jumping onto a floor with a single layer of carpet on it from 10 feet up, or one with 3 inches of foam rubber- - - -which one will be more painful to land on? That's what's happening to bearings, etc. with a multi-weight oil. To prevent hammering of parts due to excess clearance in a worn engine, it needs the physically thicker oil to act as a shock absorber. I'd reccomend using about 2/3 of a crankcase full of 50 weight, and add a couple of quarts of 10W-30 or something similar in cold weather for better cold start lubrication.
Jerry
