3406E burning water but not losing pressure when pressure tested

Sounds like condensation to me. For water to come out the blowby tube you'd more than likely have some pretty milky oil.

 

I had an ISX do that to me once. Absolutely could not find the leak. Held pressure for days no matter what I tried.

No lie, got to the shop on the 4th day (about 30* warmer that morning) and found coolant coming from #4 cyl

 

Did you bar the engine over with the pan off? Maybe a pinhole in a liner, up high? Just a thought.

 

A pin hole in liner usually will pressure up system really bad if toward the top as it’s forcing compression through the hole. Water pump is a thought but you can see the trail out of it. I’ve never seen a compressor fail to put coolant in oil on a CAT but that doesn’t mean it can’t.

A head gasket rarely fails from fatigue. They fail from poor install procedures or low liner height which causes poor clamping force on the fire ring. Too high will split the fire ring. The compression blows past the fire ring on either side of the gasket and past the rubber grommet water seals. That is what causes the compression in the cooling system. Once it over comes the cap pressure you get the bubbles in the water bottle.
This also causes very little coolant to oil transfer as the grommets will continue to do their job till the heat gets the best of them.


Very trace amounts of coolant manifest as steam in the blow by tube and after shut down it will appear as small drops of water in the blow by tube. As bad as it sucks you’ve missed something if your already getting coolant transfer. Sometimes all is well till you pull the head and it cracks a liner flange going back. Either way it’s gotta come back apart

 

That is in spec but too low. They do offer a thinner spacer plate but it needs to be that low and level across the board or it will split a fire ring or crack a flange