6.7L 07.5 leaks coolant with EB on

[Rogan]

Wondering if it isn't the EGR cooler.   Started the truck up the other day, park brake on, hit the cruise, then set..  idled up to 1200, EB on, I let it warm about 5 mins (was 19F out). 

Came out to get in it, and saw a puddle of coolant toward the RR of the engine...  chased it down, it appeared to be the fitting where the EGR cooler hose hooks to the vertical steel nipple out of the head (just forward of the heater port)..  Drove down to Auto Zone for a jug of coolant, left it running, no high idle, no EB on..  came out, no drips.   Topped off the overflow jug and monitored the truck the rest of the day for leaks; none found.

 

The next morning, I did the same thing.  Came out to leave, 3 puddles:  same as before at RR of engine, but also one at LF and one at RF of engine.   Further inspections found the upper coolant hose at radiator leaking, as well as pushing coolant at the cap/overflow hose connection..

Turned off EB, dropped idle, let it idle for another 5 mins.  Leaks stopped..

Think this is back pressure pushing through the EGR cooler or something?    Engine has about 1500 miles on a full rebuild.  Never leaks or loses coolant unless I force the above scenario. 

 

Thx