Or not. Good luck. Hope you have a warranty.

The vehicle is still under warranty. Driven only 25,000 miles.

****edit*** Just realized it is an E70 and not anE53, changing info!

I would NOT expect an internal leak unless the engine was overheated, but the I6 engines do not like being overheated and overheating definitely could cause head gasket problems.

From the sound of it you just need a different/more experienced tech to look for the leak, or to just find it yourself. (if you have warranty just tell the service manager and/or shop foreman this is a return visit for a leak of substantial coolant loss that hasn't been found yet) If you are out of warranty and want to try tracking it down yourself I'd start by removing the front plastic under-panel/skid plate so you can get a better look at it from underneath as well as see where the drips are coming from. Some components don't leak under normal static pressure test but only when engine is running, and some only leak when engine is cooling off but still under pressure etc. etc. etc. making it hard to track it down. The good thing is BMW coolant usually leaves a residue behind where it leaks from making it easier to find those intermittent leaks.

This engine uses an electric waterpump, which is at the lower passenger side corner of the engine. If there are ever any faults stored for the waterpump like "speed deviation" or "BSD communication" the pump itself should be changed, but you would have other issues with that besides coolant loss. There are a LOT of coolant system hoses which for the most part all have the plastic ends with o-rings in them for sealing... not prone to leaking at low mileage, but if they are leaking you would see the crusty slug trail looking residue.

Also, after a drive where you are using your heater park in the garage and leave it running for a couple minutes with the heater still on, if the heater core is leaking it would be dripping underneath by the transmission area from the spots that drip condensation water from the AC during the hotter months. The heater core would not show up in the static pressure test in the shop because the heater control valves are closed when the vehicle is turned off.

So in summary, I'd start by removing the front plastic under-panel, do a good inspection from underneath with bright flashlight to look for signs of leaking, drive to full operating temperature with heater blasting then pull in garage and look for leaking underneath with it still running (or at least key still on to keep heater valves open if you don't want it running in your garage for too long) and heater still on. (fan speed can be dropped to low if key on/engine off) And if there is any signs of leaking from the heater core you can tell they dealer service dept. that it only leaks when you run the heater.

Refilled 1 liter of coolant yesterday. The vehicle is losing about 1 liter everyday. Service appointment is next Monday. Hopefully it's ok with refill until then.

youre losing that much a day and dont have any on your driveway?? no steam rising when its warmed up? billowing smoke? old isnt looking milky is it? good luck. let us know what they find

I could find little bit of drop on garage floor, but no steam. Very curious where it's long from and to and frustrating.

idbe happy if its on the ground. thatd mean your not losing it internally. hopefully youre talking hundreds not thousands.

Because the vehicle is under warranty, I won't pay a dime, but I am worried if they cannot find the leak again and let me go.

Does it help if I escalate it to BMW NA? I heard they had a regional master technician or something.

took the dealer 13 times to finally figure this out with my 2004. I bet this is the posters issue as well.

If it is indeed losing 1 liter a day just tell them that and don't accept it back until they find it... If the tech can't find a leak of that caliber he can't be much of a tech and they should give it to someone more qualified or get the foreman to help him with the diagnosis/repairs.