Well, things got worse...I am thinking I have a bad heater core. I was looking at the hose to see about the replacement. Put the car up on stands and ran it till it got warm....now this.....coming from pretty much at the transmission. The only thing I can think of that is back there is the heater core. If I am not mistaken, that is an engine out kinda thing.

 

Look above at the back of the driver side cyl head, by the vac pump, there is a heater hose that goes bad often on our beauties. Also a hose that is under the wipers that can sometimes leak aswell.

 

thing is this leak is new, right?
​​​​​​You started with discharge under exp tank got a pressure test and now this under driver side rear.

See if $5 o-rings are now leaking or if the plastic parts cracked under pressure. It's a normal 100kMi tune-up parts.


The initial leak may well have been simply the tank cap relieving heat soak pressure.

 

Not the ones under the wiper. I need to cooler to get an eye on the ones behind the Cyl. My need to charge my borescope too....

 

@5soko The hose by the pump...is that the Engine Out one?

 

Dag-gone-it! I had all these ideas, and you had to go and find the leak(s). But I don't care and am going to state them anyway!

1. An easy and cheap test for a blown head gasket is to use a Block Test Combustion Leak Test Kit. With the engine running, you check gases in the coolant reservoir for combustion gasses. If the liquid turns pee yellow, you have a blown gasket.
2. The leak test described was for the cooling system; not a compression or cylinder leak-down test.
3. The dual or split cooling system is for the engine and intercooler, not the engine and turbos. Turbos are cooled with the engine.
4. When the coolant was replaced or filled last, was the vacuum fill process used? If not, an air pocket could form, but I would think driving around a bit would allow the air to migrate to the highest point, which is the coolant tank.

 

The bad boy is USUALLY the heater shut off valve for the coolant from bank 2 rear azz to HVAC heater core, it will crack over time, see below item 220 :




If yours is still original to the car, it will have the actual electric valve to do the OPEN/CLOSE of coolant flow.



However, the above is supposedly not sold anymore. Status is back ordered if you check here :
https://www.mbpartsexpress.com/searc...tr=A2782000831

.

What they will sell you is a NON-VALVED pipe. Pipe only, like below :



As how the ECM or the module handling this shut off valve when there is a "missing" valve detected as open circuit when and if using the newer pipe without the electric valve,
you need to test it with Xentry.


One bad shi-et when using this pipe only is, your heater core will always be flowing hot coolant and that in a hot country/region, is a BAD BAD thing for overall
HVAC cooling efficiency. I have by-passed my HVAC heater core, because me in the tropics and I do not need heater for my HVAC.


==============

One more item will crack for sure and leak coolant, overtime. If and when your car has the heated windshield wiper fluid option.

Item #150 . Ignore the P/N for now, as I do not have your VIN, so the #150 P/N below is probably not the one with the tee for heated windshield wiper fluid.



Here is #150 with a tee




The crack part of #150




=====================


This is the coolant flow and parts handling the coolant, starting from Bank 2 rear azz, that heater shut off valve.




The false firewall ( heat shield ) can be removed, read post #3 here : https://mbworld.org/forums/w212-amg/...ml#post8737737

=====


If you intend to keep your car for say 5 more years, replace every damn coolant hoses and tee fittings if plastic.
I have replaced all of my hoses and plastic fittings, even for radiator and aftercooler, and both coolant bottles, except 3 regions, where latest by 2026 if not next year,
those 3 regions shall be done.

If you want beauty sleep at night, till 20th year old your engine would be, the last horror show you must deal with is the item #20 and #50.
I suggest latest by year 15th, do the #20 and #50. Its a BIG BIG job. These two seals if they leak, it will mix coolant with engine oil. Those two are coolant seals crossing oil bath timing chain region.
The #20 has bad history TSB for earlier models of M152, M278 and M157 engine. I am attaching its PDF.




Your #20 and #50, is the equivalent region I would need to do for my engine too, along with 2 more regions. Mine uses 2 o-rings, not the unique molded seal like your engine uses and has no
TSB for it.

My engine is M276.820
The other 2 regions are : The engine oil cooler gasket ( not a fun job for my engine ) and the 2 hose/aluminum pipes combo for 2 turbochargers coolant circuits.

Not related to coolant but related to oil pressure is the oil pump o-ring. Oil pan/baffle to oil pump has an o-ring, that will get hard and seal bad, the oil pump will then suck air and you loose oil pressure.
Depending 4-matic or RWD only, the o-ring #45 or #50 is what I meant.




I already have on hand new oil baffle with the o-ring. My oil baffle is more complex design, long travel for the oil thru "snorkel" is scary, minor seam cracked will cause air bubble
too.


Remember, our W212 is aging and components will start to fail.


Happy troubleshooting.

 

dang.

 

@S-Prihadi I can not thank you enough for the very detailed post. Again, you amaze me.

I got to thinking (at like 3am)....I KNOW I have only had a leak at the area near the over flow...I KNOW that I found a coolant line (it will be here today, as mentioned in this thread). Then, doing my "due diligence" I lifted the front of the car, I removed the under car shields and was working to take off the pass-front wheel so that I could get a view from behind the splash shield.

So...here the car sits....in the best case scenario....hmmmmmmm.....I wonder why all of a sudden the leak seems like it is coming from further back on the car......

The video for the CLS550 - I am so thankful that my original symptoms are not the same, I can not find any coolant in that region...BUT - may replace that anyway (as you mentioned). I am in there, I have it apart - may as well do it.

 

in this video you're getting coolant on this wire harness/plug - what harness is that and could that be contributing to your misfires (electrical)

 

I only had the misfire that once....but, very valid point. On may way to Gainesville Mercedes (if I can get the hell out of the clinic)....we shall see in about 90 minutes if it is just the one culprit (and order more hoses)...

 

I often take a look at EPC to see my/our engine weak points, the plastics or aluminum pipe with plastic end and the hoses with plastic end.... handling coolant, engine & tranny oil and brake fluid.

The problem with EPC is, some components are placed all over the place, not all under the heading of say Cooling System or Heating & Ventilation.
The heater shut off valve due to it being an electrical device, it is under "Engine Electrical" as you can see from the EPC page title and people can miss that when searching under
"Heating & Ventilation".

Good to see/read EPC and enjoy it like a novel

Agree with Peter......
If the leaking zone is at the heater valve shut off valve or the hoses from it to false firewall, the crankshaft sensor can be effected ( albeit connector is waterproof ), as it is then at the wet zone.
Misfire can come from crankshaft sensor with mild error, like distorted signal.

The green circle is the heater shut off valve. The red circle is the crankshaft position sensor.



.




Our crankshaft signal is a very "tight" one. Its a 58 pulses per revolution including one being very long . While at idle of 650RPM, one teeth signal is only 122 microsecond if the valley
and/or 1.4 milli-second if the peak/hill.

If say crankshaft sensor get its signal distorted somehow intermittently, 1 "missing" valley or peak is equal to about 5 degrees of crank revolution. Missed 2 , that is 10 degrees off, which can
lead to misfire.

Green arrow is 1 revolution of the crank



1 revolution, zoomed.
.




The valley, 122 micro second only. I think the ECM reads the Peak/Hill.

 

Got it

 

Get the OR clamp for the hose, the existing will cause a leak and damage tank nipple.

 

Well, new pipe installed. Still a leak at the rear of the engine. Seems to be in front of the firewall...now, to take the wipers out again and move that heat sheild......

 

So.....I have the "Fake" firewall out (what a joy that is to remove, I dread getting it back in).

I still have not found a direct source of the leak in the rear of the engine. The hose behind the firewall (connected to the oblong 90deg connector) seemed brand freaking new. Felt new, looked new. That said, the connector )through the firewall would not budge for anything...so, I smashed it with vice grips (duh).
Figuring I was going to replace them both, screw it - get it out. Looking at the physical connections, no way on earth it was coming out not in pieces.

I need to get a small dental mirror (I lost mine somewhere in the mess) to get a visual on the screw holding the other part to the DS rear of the engine.

 

I know you mentioned using a dental mirror, but do you have access to a boroscope and you can just slide camera around the back of the engine and see the problem close-up?

 

I do - and I have yet to be able to get eyes on evidence of a leak as large as I am expecting to find. That said, I have not used the borescope since I got the firewall out as I was in "remove pipe" mode. For me, when trying to find a bolt hole the mirror is more effective for line-up (for a tool) than the scope is.

 

For what it’s worth I’m not sure if you’ve done your PCV valve yet, but removing that firewall is a big part of that job and this might be a while you’re in there type of project

 

PCV is a great idea, I assume it is in the region....now.

@S-Prihadi I have the new piece that connects the firewall to the engine - do I need to remove the part (vacuum generator?) to access the other bolt? I can not visualize it, not with a mirror, not with a bore-scope, not with the vacuum line (in the image) unplugged....in the second image you can see the ball park location of the second bolt.

 

So I got to it by removing what I believe is the vacuum creator. Quite simple once that is gone and now I have a new entire conundrum. How on Earth do I get the rest of this out

 

once you get that coolant adapter removed you'll have a perfect opportunity to replace your COOLANT TEMP Sensor with a new genuine MB part. It's held in place by that plastic coolant adapter pictured above.

That whole tune-up list is...:

• 90° firewall elbow with rubber hose
• Engine head plastic adapter
• Collant Temp sensor
• (CKP?)

> WHY all this is shot?
because it is handling the very hotest engine coolant from bank2.

 

I got the piece out. Thanks to Google and a C43 forum....

So, took out the trusty soldering iron and simply melted a slot into the piece that was still in the hole. From there a pick easily caught the round gasket (that did not melt with the rest of the plastic). Once the O ring was out the rest cleanly slid right out.

Those parts are all reinstalled - just waiting for me to put the heat shield back in. All in all - this is tedious, but, not hard. Nerve wracking.....

 

Impressive work.

do you think you found this to be the source of the leak?

 

Unfortunately - I can not verify that, more and more I think that it is not....this puts the leak at the heater core...BUT, no fluids in the cabin of the car at all. I could be wrong.

All in all, these 100% are NOT "Engine Out" hoses. I am very glad that they are being replaced (as the plastic is all quite brittle). The key is pulling the fake firewall panel, a good light, a good mirror (bore scope I find to be of no use). And, patients.