I was changing oil on several of my 4-wheeled conveyances this evening and as they were draining I wondered what purpose the large oil capacity of my 420SEL's engine serves...8 qts vs 4.5 qts in my 5.7L Roadmonster. Is it a cooling issue or a lubrication issue? Does it serve any real purpose at normal US speeds?

Does anyone have a notion as to whether MB gas engines run "clean" or contaminate oil quickly, as opposed to domestic engines. I'm bored on a Saturday night and thought I'd throw these questions out there.

__________________
2002 Ford ZX2
2 x 2013 Honda Civics