Maybe when the fuel filter was replaced one of the coolant hoses that runs to or from the front radiators was damaged, or became disconnected.
You have to put some pressure on the tubes in order to clear the fuel filter.
Here's how the fuel filter is replaced:
http://www.pedrosgarage.com/Site_3/Replace_the_Fuel_Filter.html
Hopefully it just a loose hose.
Happy Boxstering,
Pedro