2016 cuminns isx15 over pressure in overflow

[702autotech]

It was asked if it was de-mandated no it is all original how it came from factory. I did find the little hose from radiator to top of reservoir was cracking when squeezed so I replaced it, I also noticed that when I pressurized the system the coolant dropped about an inch or so until I release the pressure then its back normal and when its hot the upper radiator pipe is hot as the lower one from the radiator is cold except where it attaches to the engine.

[Signature620]

Everything in your post except the cracking hose is perfectly normal.

Why don't you replace that hose and drive it for a week?

[702autotech]

I'm replacing all the hoses (had to order lower ones) then going to drive it, being haven't found anything else wrong yet, thank u everyone for all your advise and help I will update after I retest thanks.

[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.