2016 cuminns isx15 over pressure in overflow

[DVT873]

Replace the radiator cap with OEM. Test it if you can. This might not make a lot of sense but when you change the small lines see if any of them are blocked. Had a few NAVs, not Lonestars but similiar family, a while back that were cracking the reserve tanks. Lines had gotton plugged, don't remember how anymore. When the system cools down it goes into a vacumn. If somthing is blocked that can crack tanks. Vacumn cracks them, not pressure. Vacumn is powerful. Have seen barrel tanks on septic pumpers collapse when the vacumn releif valve sticks.

On yours I beleive there is a small second valve built into the cap. It is easy to see that on older automotive designs. just a thought.

I also have never had success with dye. Old school inverted pop bottle test is still pretty reliable.