hi names robert, my dads got a 2010 6.7L cummins, we did a dpf delete, stage 2 AFE CAI, smarty jr JR65, sinister diesel egr delete. he tows 18 thousand pounds almost everyday and when he goes into 6th the temp start to free game, goes from 95-96 to 101 and we got coolant going into the over flow bottle but its not going back into the rad :/ were not loosing any coolant anywere, we switched 3 rad caps, two 16 PSI and a 17 PSI rad cap and still nothing... someone please help!!!

 

its due to high coolant pressures, causing a high pressure spike and pushing the coolant out, the cap isnt ventedand thats why your not getting it back into Radiator.