The impossible to solve overheating problem

I might have got a time for a garage to check if there are high levels of co2 in the coolant tomorrow. Unfortunately the garage that could pressure test the system dont have another time for a few weeks.
Also test started the car today and immediately inspected the exhaust very closely and Im not sure if Im imagining it but it looked slightly white, when I held my hands at the tailpipes they became a tiny bit damp, I wouldn't say it was obvious in either case but still.

Anyway, will try to get the coolant checked for co2 if possible tomorrow then do some of the tests like checking the system for flow, heater core, flushing it etc. and see where I end up.