If you had a head gasket problem you would see brown/white mayonaise type stuff on your oil filler cap and maybe on your rad cap.
hi mate, yeah ino loads of people are asking me about mayo, but no problems with that. thank god!
i probably just worry too much, but i would rather prevent it rather than letting it get worse.
however i did look at my header tank today and it had gone back up very slightly, so i was like... what the hell??
maybe it just fluctuates? but surely it should stay at the full mark and not half empty?
Your best bet is to park on a flat spot at nite and just get a felt tip pen and mark on the expansion tank where the level is ( when cold )and check it before you start the car up the following day just to give you and idea how much coolant loss is happening....
I would be very surprised if its your headgasket gone as there would be more signs ( like the mayo )
get a small mirror from your mum/girlfriend/wife etc and just hold it under your water pump and see if there is any signs of leaks there...
p.s dont forget...your expansion tank level WIll go up and down when the car is hot or cold.....