2018GLC300

Hello everyone
I noticed a blue/green fluid had leaked from front left side ( under the washer fluid reservoir) , MB service said the reservoir is probably cracked and needs replacement.
Checked Engine coolant reservoir , just to make sure it wasn't the source, it was full, done at service in Jan.
The car is always garaged and not used much and after its last service in Jan , it was mostly unused , but there were a few very cold days( -15F ), maybe garage was at 5F

Anyway I refilled the washer fluid yesterday ( 65 F outside air temp ) and didn't see any leaks, drove it around to get the compartment warmed up , still no visible leak on the floor.
What might have caused this leak ? which I'm not able to repeat now.
My theory the washer fluid reservoir has small cracks that contract sufficiently only in very cold weather, to cause noticeable leaks?
Any one had this issue , any thoughts ?

TimC300

What other fluid is blue/green in the car? My coolant is that color but its a 2010, I think 2013 is a redish/pink color maybe. If you pour some windshield fluid on the ground does it look the same as the leak you found?

Coolant does flow through the windshield fluid reservoir to heat it up. Theres also a sensor that goes thru the side of it sealed with a gasket.

With the undertrays I know at least for me its hard to pinpoint leaks.

2018GLC300

Thanks TimC300
Didn't know the coolant has a sneak path through the washer fluid system, they are supposed to be good till -20, but I guess MB probably has insured it works at even colder temperatures.
I did check the Coolant reservoir , and it seems its at the full mark. So at this point it's probably not the source.
As for the color of what had leaked and dried up on the garage floor, its a bit subjective. To me it was blue-green.
So far the garage floor has been clean since I refilled the washer fluid.

I did question the MB service person, because before I saw this leak this month, the car was in for a Service B in Jan ( was very cold then ) and during that visit , additionally on their recommendation the Coolant system was flushed, but they obviously don't think this leak had anything to do with the coolant flush procedure, and claim its a washer fluid reservoir leak.

TimC300

Could be nothing, or snow in the wheel well melting. There's hoses and pumps for the windshield wash system, even more hoses and connections if you have the headlight wash system.

2018GLC300

It was definitely dried fluid on the floor. Luckily this car has a plain vanilla headlight, no wash system on it or any other complexity..
I also heard that if you over service the coolant system, it can expand and dump it out , ( Recall I had gotten the coolant system flush in Jan ),
don't know if that's indeed a fact and where exactly it would dump the excess coolant overboard, and if that's what might have happened here.

gamma300C

My 2009 C300 had a similar small leak in the washer fluid tank...removing the driver's front fender liner and moving the lower black plastic splash panel revealed the bottom of my reservoir. There is a molded seamed running up the side, hardly visible, and it was weeping so slightly, a drop would form and take a minute or more to reach the bottom of the reservoir, then more time to finally drop onto the bottom panel and eventually a drop would finally hit the garage floor. I only noticed a small, in my case, blue stain on the floor one evening. My fix was to clean the area with 90% isopropyl alcohol after roughing up that split seam slightly with emery paper, then apply Permatex black RTV. I did this with the reservoir full....a couple days later there was the slightest residual seam wet spot which another smear of RTV fixed...no leaks after 8 months.

2018GLC300

Thanks gamma300C. That sounds like what could have happened here , in the sense that its not an immediate or heavy leak even in my car.
Will let you know what I find.