coolant issue

[Shorty S91]

Evening guys,

Ive been keeping an eye on my expansion tank for a while but yesterday I went to the the kids to nursery and was prompted with a low coolant level warning. So i checked to see where it was at and there was just under half when I always keep my tank topped up.  

I took the cap off and started the car to see if there was perhaps an air lock in the system. Ran the car for about 10 minutes and held it at 2000 rpm for about 2 minutes. The level returned to normal. 

Checked it again today and the level had dropped again. there is no staining around the water pump and I cant see any wet patches on the ground or in the engine bay. The car is not over heating and still runs smooth however I have noticed a small amount of bubbling coming through the return pipe back into the expansion tank. 
Any ideas???

[Shorty S91]

Update:

Went out this morning to have a good look over the car.



The bubbles were appearing in the top return hose when the cap was off while the system was bled. Bubbles have now stopped when the cap is.


Pulled the oil cap off and spotted some mayo on the cap and instantly thought the worst  given the fact that coolant was going missing.



Me being me went into fault find mode and took the rocker cover off.




No mayo in the cams or anywhere else. Just a little bit in the rocker cover which is fairly typical of vauxhall engines. No mayo on the dipstick either. Glad its not the head.

What I did find was a really small crack in the expansion tank though 

[tucpal]

Lets hope that is the issue

[stigeye]

Where is the coolant full/ low lark i.e is mine low, I've put a couple of guess lines in?

[Shorty S91]

yeah thats it mate. You get a warning if your coolant gets low and you should always top it up when its cold too.

[stigeye]

yeah thats it mate. You get a warning if your coolant gets low and you should always top it up when its cold too.

Cheers mate ;-)