Use exactly the weight that Mini recommends. http://www.ehow.com/list_7739452_list-mini-cooper-approved-oil.html
The 2004 MINI Cooper has an inline 4 engine.
The 2004 MINI Cooper has a 1.6 L base engine size.
The 2004 MINI Cooper has a 5-speed manual.
The 2004 MINI Cooper's engine produces 115 hp @ 6000 rpm.
The 2004 MINI Cooper's engine produces 110 ft-lbs. @ 4500 rpm.
The 2004 MINI Cooper runs on premium unleaded (required).
The 2004 MINI Cooper has 16 valves.
The 2004 MINI Cooper is a gas-powered vehicle.
The 2007 MINI Cooper has an inline 4 engine.
The 2003 MINI Cooper has an inline 4 engine.
The 2005 MINI Cooper has an inline 4 engine.
The 2008 MINI Cooper has an inline 4 engine.