Yeah I mean it should have shown itself by now...
I refill [too strong of a word really] her watching it like a hawk. I thought I found it only for it to never repeat so that must have been melting snow. I've driven her and noticed nothing but the cap... Ordering a new one.
The thing is the low coolant light went out the first time I topped her off and then returned only to never shut back off... PITA!!
I'll report back...
CRAZY ASS SH**!!

Sent from my SM-N960U using Tapatalk

If the cap was leaking, and you're using BMW antifreeze, you should have that tell tale white residue from after it dries. While I agree your cap could be faulty, unless you have residue on the top of the expansion tank, I'd say you have the well known slow leak from the bottom or side of the tank.

When my tank went bad, it was in a location that I couldn't see any residue. I just knew I was having coolant leaving the system and decided to try the tank first. Especially since it has been mentioned on here a lot too.

No, I’m sure it was the tank, the coolant was leaking from underneath.

*UPDATE*
Started with a new expansion tank cap to corner this ghost coolant leak. Does anyone know if the low coolant warning goes is supposed to go off once the expansion tank is full? New cap. No change. Dead of winter...

Sent from my SM-N960U using Tapatalk

System is full when the "pecker" sticks out. The low warning should come on when more than a pint or 1-1/2 low. If you have a low coolant warning when there is coolant you can see in the reservoir, something is wrong with the sensor system. (unplugged, stuck float, etc)

Need to have the warning light turned off. Then if, after a new cap [just replaced] I'll continue with the process of elimination.


Sent from my SM-N960U using Tapatalk

AHA! I can never NOT see the level of the coolant. I add a few ounces at a time to fill it. This brings a new point of view I will follow through with. Thanks!

Sent from my SM-N960U using Tapatalk

What year is your E70? There no "pecker" on my 09 E70 N52 - just max and min marks.

Either way, what's next, a pressure test?

Oh sorry I mostly work on e53. They have a float for min/max.

Either way the low coolant will be for far far lower than min. Usually if you have erroneous low coldness l coolant is when the sensor connector is broken or a wire is broken.

On e53 I think the sensor can be pulled out of the bottom. It goes up inisde a sealed port so there is no seal to leak

Yeah. Sorry guys. My e39 has the "pecker" not the e70.
MIN/MAX... Got to check hoses and the pressure test... It's almost a ghost leak. SO. TINY. I'll find it...
Thanks!

Sent from my SM-N960U using Tapatalk