It's not impossible the head is cracked but it is very unlikely if it has never over heated. I suggest you get the cheaper and more probable problems worked on first, before taking the head off. That means the thermostat and EGR cooler need to come off for examination and testing. (Test the thermostat by putting into boiling water.) If both are OK refit them and refill with coolant, ensuring you eliminate all air locks. Air locks can be very difficult to get rid of. I used to apply vacuum to expand any air to the reservoir, but I appreciate that few people have the ability to do so.