Isx15 popping radiator caps

[Scooby d]

I was getting a tiny bit of pressure in my cooling system just once in a while. Fought it for months with just an occasional hose leak or cap gasket leak. Did several tests and couldn't pin down a problem. It turned out to be #6 liner had sunken and all other 5 were just to low. 380k miles on a 2012 cm2250 . If its your liners search around on here for correct liner heights. Cummins original specs were a bit low.