When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I've had a slow steady loss of coolant for the past two weeks. Car drives very well, no unusual smells.
I did a quick pressure test and I couldn't find anything from the radiator or any hoses at the front. I got under the car and saw pink coolant residue under the left side of the car. On the photo, you can see it on the left lower control arm, brake lines, and dripping through what appears to be part of left side firewall near the strut
. From up top, I can't see anything. I popped off the plastic cover to the brake fluid reservoir and master cylinder. Nothing to see from there.
Where is the likely coolant leak? I've heard of a leaking changeover valve for the heating/cooling system behind the firewall. Would this cause the visible leak?
From above, I think I see some moisture on a O2 sensor and the O2 sensor wire so I'm not so sure this is confined behind the firewall. Nothing in the valley "V" above the engine.
I'm not a mechanic, but I don't think coolant, by itself, is pink. The only red/pink fluids are the power steering and transmission fluids. Given the location, maybe it's a mix of power steering fluid and coolant. Just a guess...
I'm not a mechanic, but I don't think coolant, by itself, is pink. The only red/pink fluids are the power steering and transmission fluids. Given the location, maybe it's a mix of power steering fluid and coolant. Just a guess...
I’m diagnosing a coolant leak because I am adding pink coolant every few days. I checked the area and on the other side of the metal shield is the exhaust pipe with O2 sensor and there is no coolant to be found. I think the pink crusted coolant is a red herring and may have gotten there by splashing the last time I drained my radiator a month ago to replace the recovery reservoir because of a malfunctioning coolant level sensor. There are no leaks to the hoses at the reservoir or in the front. Because the problem (clearly a coolant leak) started after my own service of replacing the recovery tank, I’m going to do what I should have done first which is to get a new cap for the reservoir. I’ve gone crazy trying to locate the leak when I should have just replaced the cap from the beginning. Nothing is hissing or leaking with a pressure test. I wiped off the pink crust and if it reaccumulates then there is a real leak in the rear engine bay that I’m having trouble locating.
The leak is real and dripping from the metal heat shield/panel just above the brake lines in the picture but there is no drainage seen from within the engine bay. This is in the left front wheel well, just above the rear control arm. This means there is a coolant carrying tube behind the heat shield and possibly behind the firewall. Nothing is visible from inside the engine bay, so the leak is somewhere behind the heat shield and possibly draining from behind the firewall. The bottom black plastic shield under the engine is bone dry except at the edge where the leak is visible so I know it's not in the visible engine compartment. I have to suspect this is a water leak around the heating system or heating control valve. Time to remove the windshield wipers and get behind the firewall. If this doesn’t show anything, it’s a trip to the mechanic.
I finally got off my **** because I was sick of driving the back-up W203... not that the W222 was unsafe to drive. I passed a borescope behind the firewall underneath the windshield wiper plastic drain shield. Crusted pink dried coolant is seen and it does appear to be a cracked heater control valve, MB part number 2308300084. This is a known source of coolant leaks behind the firewall on many Mercedes with the M278 engine, and as I'm reading on the internet, it seems to be the most likely source of a coolant leak behind the firewall. It's a 60 dollar part and probably less than 2 hours of my personal time. I'll post pictures when I get to it.
@bkdc Did you ever get around to doing the repair? Our '14 S550 90K miles seems to now have the same issue and I'd appreciate any advice regarding it. I've seen some guides on this thread but want to know of any gotchas before attempting this.
10-30-2021, 03:16 PM
