Soot in overflow tank

[tree98]

1/2 - 2/3 gallon of coolant a day is a lot. You would definitely see that in the oil. If your burning it you should see it in the exhaust since you don't have a dpf(cm870) to gobble the smoke. You gotta have some other symptoms ?? There's only 3 places it could go, in the cylinder and burned, in the oil, or on the ground.