When the beast is cold, try bleeding the radiatore. There should be a bleed screw on the top corner. It may be on the left as you lean into the engine bay .. but possibly on the other side.
Unscrew it slowly until air or coolant comes out. Don't unscrew it completely since if it comes out, you'll have a job getting it back in with all the coolant ****ing out.. (unless you like "depth-charged submarine" moments..
If just coolant comes out, then that's good. It could be that your car just had low coolant. You need to see if the level is stable or if it's going down.
If it's going down, you need to work out where it's going.
Check that it didn't lose any:
>> Out of a defective header tank cap - Do you have stains on the bonnet lining?
>> From any leaking hoses - Look for white/pink/green stains at the hose joins
>> From a creaky radiatore - Look for streaks down each side and check if the radiatore support mount is wet.
>> Heater matrix - is the carpet damp on the left hand side (passenger's right foot)? Stick a rag on the end of screwdriver under the centre console where the airbag switch is and see if it comes out wet or pink stained.
If air comes out of the rad'... then use the car a while.. let it cool down and repeat it once again. If it clears.. and you get just coolant coming out (2 bleeds should be enough) then the beast is okay.. Keep an eye on the coolant level as above and try to work out where it's going.
If it still bleeds air then it's certainly a leaky head gasket... nothing else. You can try running it a while depending how bad it is... but the cooling system is going to be under pressure these next 3 months and it's likely to just let go on you when it's least convenient.
Fingers crossed it's just a leaky radiatore or something minor...