2011 Mack CXU using coolant but no leaks?

You need to have it pressure tested with the proper tooling.

 

If a cup is leaking you would more thank likely have coolant in the oil but not definitely. We have a good amount of Mack gu’s in our fleet. They’re prone to coolant leaks and many of them are hard to find. What happens often is the coolant sprays on the block and evaporates off immediately leaving no trace. Check behind your egr. There’s a pipe behind it for coolant. We’ve had 2 trucks leak there and they both sprayed on the block. And we run 100% water in the coolant system in the summer for a couple days when we clean the coolant system out, coolant to water ratio won’t do anything weird except freeze in the winter

 

Have you checked the DEF coolant lines? I had the same problem but could never find any leaks until one day I drive through a terrible rain storm and hit some standing water, it ripped them clean off. I mentioned to the Mack tech the losing coolant issue and he said it was likely the root of the problem