2016 cuminns isx15 over pressure in overflow

[702autotech]

Have a 2016 int. Lonestar w/isx15, 741250 miles on it. I replaced overflow bottle about 5/6 months ago last week I noticed it was leaking from the side of it ,I noticed it had stress cracks down the side so I sealed them until my new bottle came in, installed the new bottle and cap left that afternoon and about 180 miles my low coolant light came on, never went over 210° before fan came on, I pulled over opened hood and coolant was all over from fron of truck to back of trailer everything soaked and bottle was empty also it pushed of upper hose from reservoir to radiator that tells me that it over pressurized I filled it took 4.5 gallons drove another 100 miles and rechecked it it was half low refilled again but this time left the cap alittle loose and everything was fine barely any gone, got it back home and checked it the cap was gone and was about an inch low, I was reading up on here about it, and I seen to try the bubbles in water, well I had it running for about an hour and a half at 1400rpms and idle and not one bubble, coolant did rise about an inch. Gauge stayed normal. Any ideas to help figure this out.