puking coolant
You might also have a restricted oil cooler. If the coolant passages in the oil cooler get plugged (casting sand, silicates, etc.) then the egr cooler (downstream of the oil cooler) doesn't get proper flow, and the coolant in the egr cooler flash boils causing the coolant to puke out of the degas. That is how most egr coolers start to fail. If you have access to checking the coolant/oil temp, the oil should not get more than 15 degrees hotter than the coolant, if it does the oil cooler is restricted.