cooland loss

My first GC and only got it 4 days ago. The coolant light came on after about 200 miles so I topped it up ,200 miles later it was low again and the light came on,I toped it up and started looking for leaks.
I couldnt see any, and It runs well, so where is the cooland going.
It is a 3.2 Ltr Ltd 2001 model.

Might be your water pump going bad, there is a weep hole in the water pump that will leak coolant when it goes bad, it is prolly a very slow leak and burning off on the engine.

if it is not leaking like you say, I would check for coolant in the oil, is your oil level high? does the oil look foamy ? A blown head gasket will let the coolant enter the engine. Another area, but not likey at all is , the auto trans fluid lines lead to the rad tank and if there was a problem there , coolant could enter into the trans as well.

Just did anothe 300 miles, the light came on and it took 2 ltrs of coolant to top it up.
At home, I searched for a leak,leaving the engine running, still cant find a leak. The oil looks OK dark and smooth. No puddles under the vehiclecant see any drips?

PS what is the purpose of the small knob on the top of the radiator housing(turns in line with radiator or 90 deg across the radiator top, which should it be?)