1998 BMW 328

Engine Cooling problem
1998 BMW 328 6 cyl Two Wheel Drive Automatic 141K miles

Hi there,

I am having problems with my car cooling system.
I have filled up the cooling bottle a few times but it goes all the way down in a few hours.
I have taken it to two mecanics ( not bmw dealer ) that work or have worked with BMW, and none of them could tell me where is the problem.
I thought there was a lick from a hose or the bottle itself, but so far could not see it. The temperature gage is fine, so the car is not over-heating.
I have tighten the bottle lid thinking that the problem could be because a loose lid. But did not work.

Thank you very much in advance for your help,

Tomas