[Grobbo]

For those that can't use google:

•Typical symptoms of a blown head gasket may include these: bubbles of air coming up into your radiator (remove cap before starting); a leaking radiator; milkshake-colored oil; overheating; rough running; coolant or oil running from head; spark plug(s) that have a green tint (if green coolant); white-colored or sweet-smelling exhaust.
•White smoke from your tail pipe, or loosing coolant through your overflow. Take the cap off and rev the engine, look for bubbles...
•A dark smell in the radiator. High back pressure coming though your radiator cap.

Sounds like it's not really the easiest diagnosis!