2004 4.4i coolant leak

[wydra]

Hi guys,
It seems i cant catch a break. Now my car is dropping coolant.

Its bit of a strange one though, when the car is running or even warm it doesnt appear to be leaking. It only seems to be when the car sits for a few days.
If the car sits in the driveway for a few days there will be a big puddle under the engine and the "check coolant" warning will appear and I need to add fluid.
If i continually drive the car and not let it sit it is fine and will go a weeks before i need to put any more fluid in (usually because i let it sit a few days and get the puddle under the engine)

I am finding it hard to find out where the coolant is coming from because it only leaks after sitting for a while. Has anyone else come accross this?

The leak is hitting the ground towards the front left of the car but it might be flowing along the bottom engine bay cover and coming from anywhere.

Any ideas?
Seems very strange it only happens when the car cools right down.