CM871 Lots of oil in coolant

[TheBud]

Have a Kenworth with a CM871, had oil seeping into coolant, small amount of oil, replaced Oil Coolers a month ago, problem solved, zero oil in coolant.

Yesterday truck pulled into the yard literally pumping coolant and oil out of the overflow tube on the coolant reservoir, pushed 3 gallons of oil through the coolant system. There is novisible coolant in the oil. Removed oil the new oil coolers, no visible issues, having them tested. I suspect they will come back ok. What else would cause it to push that amount of oil into the coolant in a short amount of time?