Found an article:
Anyone know if this affect 6.0 L engines?
My 05 escalade 6.0 having slow coolant loss, no apparent external leak.
Already did: waterpump gasket replace, which used to leak from.
Still loosing but slow.
09-23-12, 10:34 AM
Check your oil! If its over full then thats were its going!
It was the heater hose connector to the heater core in the firewall that was leaked.
Thy call this connector as QuickConnect thingy.It leak from the outlet line hose, not so big amount.There is no crack nor apparent damage to the connector, i assume it was the rubber O ring that is worn.
Solution: Remove the connector and apply plumbing tape or sealant tape and reinstall the connector.
No More leak.
09-25-12, 02:14 PM
If you look at the following link he included pictures with the same problem as you
09-25-12, 02:30 PM
Yeah i recently changed both of those tees, the white one started turning brown so i changed it, it was only a matter of time before it cracks. Part numbers for the tees should be 15055343 and 15055342