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JP57

Hi. Everyone.
Isx-15 mandated, def-egr 640k miles.

About 7 months ago coolant started coming out my reservoir tank (pressure relief cap) got to the shop, it was tested coolant had gas, so head was removed tested turned out to be a bad head. Got a new head from cummins (5k) all new seals and gaskets, drove good for 7 months maybe like 50k miles or less and my last trip coolant started to push out again. BUT... only when building pressure for example heavy loaded and going up the hills for a good while coolant will drop half tank , when i stop and open the cap,, pressure exits the tank and coolant goes back to normal... another issue, my 2nd tank that has pressure relief cap usually empty, but this time it was full of coolant, so i noticed if i add more it over flows and blows it all out, so i stopped filling the 1st tank because when i drove on straight roads and for long the coolant would travel back to 1st tank and stay level. Another hill comes up and again same issue, coolant goes back n forth between tanks or out the cap... in about 2k miles i put in 2-3 gallons of coolant and i did spill some because i had my fill cap looose for pressure to exit but sometimes it was to much and coolant wouls come out...

I went back to the same shop that did work, 2 weeks at their shop and they could not find any issues, i dont know if they full of it and dont wana do warranty work or really didnt find any issues...

Any help really appreciated.