PowerMac 11,2 is the Late 2005 model, that's correct. I think the person in one of those links who said his DC 2.3 was leaking was mistaken. They are not liquid cooled. The pipes you are seeing are air heatpipes, not coolant pipes.
Also, the service manual for the Late 2005 models has this to say about the liquid cooling system (verbatim from the manual): "The Power Mac G5 (Late 2005
Quad) configuration uses a liquid cooling system (LCS) to manage the temperature in the computer." Notice how it only references the Quad model - the only Late 2005 model that's at 2.5 GHz or above.