In Reply to: oil weight posted by mark '72 golf on September 08, 1999 at 23:57:50:
50 grade is thicker than 40. It is generating more friction between parts, thus creating more heat and rubbing power. A loose engine will need a thicker oil grade. Also the wider the gap between cold and hot (10w40 VS 10w50), the more additive there will be in the quart, the less oil.
There are different theories when it comes to oil grade selection...