Ok so I have been digging in the forums and worked every possible solution to my trouble. I have a 2012 6.7 with egr delete, no cats, no tuner just programmed to remove sensors. It’s having the strangest cooling system issues. As of right now it is puking coolant into the overflow and not returning it. You can open the radiator cap the next morning and the radiator is under pressure. I have changed the water pump, belt thermostat twice, radiator cap twice, full system flush and it was running fine for 800 miles, I go to put the camper behind it at an added weight of 9300lbs and pull it 10 hours across North Carolina and all the sudden when I go to slow down from 75 to a 55 it start to heat up quick. So I throw it in neutral and mash th throttle and she opens up and drops the coolant down to 186 from 210. Hmmmm :confused013: so it pulls fine for another 2 hours to the campground. I decided to do some checking and the radiator hoses seemed fine. But the next day no camper attached same thing. It would be fine and then the temps would start climbing, throw it neutral hit the throttle to run up the RPM’s reall quick and she would start cooling. My thoughts were a collapsed hosed and I was pushing it open by revving the engine. So I order the hoses and a bucket from Amazon straight to the campground and change the hoses. Bottom hose spring was not all the way in place and very soft close to the block, so I think aha! Truck seems to be fine no issues pulling and then I realize it’s not returning coolant from the overflow. So I manually transfer the fluid back with a drill pump manually. I think of the system has a vacuum leak(I had actually broken one of the thermostat housing bolts on the last thermostat change). So I drill it out and replace the bolt even though there were no signs of coolant leaking. I also made sure the reservoir hose was clear and put hose clamps on it to ensure that it wasn’t sucking air into the system instead of coolant. So my fears now after all that it’s still pushing coolant into the bottle under load and I think ok possible blown head gasket. No water in the oil no oi in the water, so I order a block tester kit to check for exhaust gases in the cooling system. I follow all the instructions get the engine up to temp crack off the radiator cap and test for more that a 60 seconds and the liquid stays blue no change in color at all. :frown2: :scratch head:.... What next? Where do I start? I’m blowing coolant out the reservoir and temps don’t show bad, It likes to get to around 197 before opening the t-stat which is a 190 Cummins oem. Any ideas are greatly appreciated.