New overheating problem

[Ivan141]

AArrghhhh...
Today I spotted a bit of fluid under my car in the parking lot.. felt and smelled like coolant so I checked the level, which was fine.
On the way home it started overheating again at the first traffic jam, so here I am at NoHachi's place waiting for the traffic around here to quiet down again so I can drive te car home without crawling.

A closer inspection revealed the bottom half of the radiator to be filled with coolant, and there is a small leak trail going down the side of the radiator.
the fluid level is still good, but y new radiator cap indicates that it has already been venting excess pressure.

I know I need a new radiator, but I find the symptoms a bit weird if it's only a leaking radiator..