Have Volvo Questions? Ask a Volvo Mechanic for Answers ASAP
If there are no visable signs of leaks, it sounds like the coolant is leaking internally in the engine and coming out the exhaust. You need to have a dye test done on the vehicle to determine if there is a leak internal. The head gasket is the most likely cause of this problem.
Just following up to see if you need further assistance with this question, if not please accept the answer and give me a 5 star rating. Thank you and have a happy holiday.
So you have discovered a leak, now you just need to fix leak and refill coolant and this should correct your overheating problem.