astrodog1

Got a 2007 R320, started losing coolant just below the master cylinder not sure if its a heater core or just a hose. Cant find any posts that describe this, anyone have had this leak out there?

Thanks,

B34chBum

Yes.

You may be able to get at the hose(s) without removing the rain tray but it would be awkward.
Really, remove windshield wiper arms and loosen the lower portion of the trims beside the windshield, to get the rain tray out.
If you haven't pulled wiper arms before, I would advise using an air chisel with a point, to vibrate the posts to which the wiper arms are attached, as you pry them off.

With tray out of the way, you can see the hose going through and between the firewall layers.
(Engine compartment has an inner firewall/sound barrier.)
There is a small section above the hose at the left back corner of the firewall, held in with 2 10mm shorty bolts, kind of like fender bolts.
Remove it to access the fitting through the firewall.
(You could try removing this panel from the firewall without removing the rain tray, but I think it would be a feat. And the fix hasn't really begin yet).

At first I though that it was simply rubber fatigue where the spring hose clamp wasn't able to compress and seal anymore.
It was leaking down the back of the inner firewall and around onto the flat area behind the wheel well (where you see it now).

I replaced the fitting going through the firewall along with the short section of hose going to the heater core, just for good measure.
BUT, I realized a couple of weeks ago that the through-firewall fitting (made of the stupid black plastic that's everywhere anymore!) had actually perforated.

I'd recommend replacing both the fitting And getting some standard heater hose for replacing the short piece connecting it to the heater core.
Fitting part number is A2515060018 "CONNECTING PIPE IN PARTITION WALL", the best I can tell. I ordered one last summer and don't have the receipt or package handy.
Might also be A2515060718. I got an aftermarket one. Here is a diagram of the heater plumbing:
https://www.ilcats.ru/mercedes/?func...81&language=en
The small aux pump is at the front-right of the motor (at left in the diagram), system wraps around to the rear of the motor where this fitting is found, going through firewall.

You can see there are 3 hose connections behind that "Partition wall", but I would bet it is the one attached to this fitting on the back side - due to vibration.

Hope this helps,
Tom