The other day it was really cold here in Chicago, as I am leaving work the "Check engine coolant" warning popped up on the dash, so I stopped at a gas station and checked. The coolant level was a tad bit low but nothing significant. It's never shown that warning before or since, and it's been a week now. Added more coolant just to be safe.. Possible causes?

 

since the actual level was otherwise not too low then no engine crack or leak so nothing serious in my opinion, but these sensors are very sensitive to even a tablespoon low of coolant and it'll fire a warning

how many miles on the car

 

Luckily you don't have a M156 engine, for which this warning will kick you into full panic mode.

 

Got the low coolant warning over the weekend on the 2016 Wagon. In the shop now. Wanted to share a couple photos and will update this thread when we get diag and repair back. It was just in for 20k recently, but went a few weeks so I think the timing is just coincidental.

Warning light initial on Friday - Saturday get in it to go somewhere, notice the light, Wife says "oh yeah that came on yesterday" check, sure enough it has spotted the driveway. Not a huge amount but enough to make a small football shaped puddle near the front of the engine. Smell checked the puddle - not much smell to it but definitely a greasy feeling - not just water - definitely not condensate from A/C. Backed it up a couple feet - left an identical albeit smaller spot in under the same place. There IS a slight coolant smell under the hood after driving, the classic tell-tale maple syrup smell. Service Advisor thinks possibly Turbo inlet fitting, they see those on occasion.

Also of interest I believe we've had the Reservoir replaced earlier as well, have to check the records. Not the first coolant smell on this one.

Reservoir looks dirty but doesn't appear to be leaking - this is probably lazy cleanup from the fluid top-ups on the 20k:


View from the top above the fan shroud - you can see the white residue and maybe even some of the coolant leaking.

 

Funny that, it was indeed the left bank turbo feed line. Apparently there is a plastic bit where it attaches to the thermostat housing, or beneath it, that can get brittle and break. Service advisor had photos of it, waiting for a text, if I get em I'll post em. Interestingly he said their sister store had it in stock because they do see these from time to time, and there's an updated part number of alleged better design that should hold up better. Sounds like MB updated the part to avoid the issue.