Bmw E60 2007 loosing coolent drastically and no leak identified

[Jay2328]

Hello all,

I have BMW E60530XI 2007 model.

I am facing an issue since February where the coolent gets low drastically. According to the measurement, I am losing 3mm of level when I drove 18kms.
I topped of the coolent 2 times went for checking the leak at workshop. The garage person had performed pressure test and he found no leak. The system maintains the pressure. He told me he went slightly beyond the threshold limit and still the same thing, he couldn't identify a leak as the pressure was holding consistent.

What could be an issue? Is anyone aware of such problems?
What to check?

Thank you in advance for your answers

 

[rssid]

Head gasket is suspect. Check for white smoke on startup or acceleration from the tail pipe.

 

[Citizen69]

When no pressure loss is detected, then its most likely a very small leak and the coolant is lost only during engine running, or it could be the coolant tank cap
Next time you drive for some time and park, do not turn off your engine yet. Open the hood and with a good light source, look around the coolant system and follow where the pipes run. if you see steam coming off somewhere or slight hissing sound, then u would have detected the leak source. Remember the radiator too, as small droplets may ooze out and evaporate almost immediately.

My previous E60 had a loose cap, and can only be detected this way and I can see steam coming from under the cap, when the engine is hot and running. The pressure loss detector the ws used was attached to the coolant tank opening and thus the cap problem was not detected