I did rebuild this engine recently. You need to purchase a WIS from eBay to gain access to MB dealer software and look up the part number for those hoses along with that sensor attached to the engine. I will look them up and attach them here.

 

2012_S550, Thank you for your kind reply. I believe I found all the parts I need. I got EPC and WIS now. See attached part list, please can you kindly review and let me know if I got all the correct parts.

Also, why in cooler vent line I see coolant leak? If it is vent line, then how the coolant get there? I am just curious about it.

 

Intercooler vent (bleed) line.

 

konigstiger, thank you sir, appreciate in confirming the vent line. I am ordering all my parts today to work on car next weekend.

I am still curious how the coolant leaking through cooler vent line? May be I don't understand all these Twin Turbo M278 engine cooling system that it has. It seems M278 engine is more complex due to Twin Turbos then my other good old S-550 with M273 naturally asperated engine, much simpler.

If anyone has any feed back or comments on cooler vent line coolant small leak, please help me here and give your input. Thank you all for your support.

 

See if attachment helps.

 

Seeking Coolant leak suggestions on an M278.
Konigstiger, your cooling handout very informative, but in my case MB does not include the rear of the engine in the handout. I believe my leak is from the rear, next to the firewall. Leak is not minor, only when engine runs. Reservoir was replaced by previous owner. Cap does NOT his consistently when cold.
I just acquired (and still learning) WIS and am concluding that my leak area is part of one of these subsections: Climate Control, Heater, Coolant Hoses.....which MB does not consider directly part of the engine coolant system. I can not locate diagrams for some of these subsections, so I am unsure what is under the windshield wiper cowling.
Do you have suggestions for location of a coolant hose (heater?) diagram that attaches/passes thru the fire wall? I was looking at section 83, but unsure. My reading around the forum leads me to believe that the leak is either a hose or hose connection near the firewall. Before I open up the cowling, I want to get an idea of what I am getting into. Suggestions appreciated.

 

konigstiger, thank you so much sir, very good document, I really appreciated it. Now I understand what this vent line does. Thank you again for your time and effort to get us information. God bless you man.

I got all my parts on order and will work on car this weekend.

Just FYI. 2012 S-550 has 56100 miles on it, not driven to much. It seem like M278 Bi-Turbo create quite a bit of more heat then my old M273 engine on 2007 S-550.

 

Sorry for late reply. additionally don't forget to replace 'Crankcase Breather Pipe' while you in there. I will attach it's part number and it's diagram.

 

2012_S550, do you know why I need vent fitting? I checked my car and I don't see any other tubing leaking coolant or oil etc. Do you have photo of it where does this goes? Is it in front area of engine where pullies are or it is in back side of the engine?

Did you see any issue on your engine with respect to this fitting?

 

Definitely anytime and any place you see evidence of a cooling leak ,that must be taken care of. No coolant leakage is acceptable at all, as that could lead to engine ruin. I don't like the part where the WIS says they changed aluminum and steel parts to plastic! But as long as the parts are new or in good condition, I guess that's okay. Cooling system is what keeps you from having to take the bus! When one of my cooling hoses sprang a leak I had them all replaced. Cheap insurance and reassurting to know that they were all new again since the car was 14 years old! When I bought my 2004 SL600, I also bought a replacement radior "just in case I needed one", and it's still in my garage. I'm happy to know it fits almosat all R230's. That said, I'm curtailing my crazy habit of buying spare parts that O don't need as I have W124 and W140 parts and others that I bought that I never wound up using, a whole section of my garage is taken up by these parts! Good luck.

 

What I've found to be true is that when a coolant hose or fitting fails it's not the only one that will fail. It's pretty warm here in the summer so if I find something leaking I'll look at that whole system to see what else might be next. The cooling system is pressurized and you should get a little 'burp' if you remove the coolant cap while the engine is cold. If not, you may just have a small leak somewhere.

 

Video covers area of interest (change-over valve) on 07 relatively same for your vehicle. Diagram shows heating water lines, 170 depicts valve.

 

Video covers area of interest (change-over valve) on 07 relatively same for your vehicle. Diagram shows heating water lines, 170 depicts valve....

Konigstiger, thank you. Your diagram helped me focus on that area. As you suggested, part 170 had been revised/upgraded to MB coolant part 2128300496 on my MY version of same M278 engine. Part no longer a 'box', more like a tube intersection.
For others trying to diagnose, my coolant leak between the firewalls (plural) appeared minor and did not seem to correlate with the puddle under the car. Result: after install and multiple tests, it seems this is the only coolant leak source. The reason is the small leak seems to have been occurring for awhile (under previous ownership). This leak runs down one of the firewalls and makes its way to the underbody panel that is made of absorptive material. The panel retained more liquid than known, then releases the excess liquid by volume or gravity. Tip: MB recommends a specific long 'snake'-type hose clamp wrench - you will need it. This part is up high, but in a tight space. I used several different hose clamp wrenches to complete the part swap. Thanks to others who have posted followups that I read.

 

Thank you all for your support and help. It took me to get vent line about 3 months. The vent line was back ordered. It is getting difficult to get parts from MB.

All installed and it is good now. No more coolant leaks.

So this vent line that get connected to Crank case and Intermediate cooler is basically to let some of the overflow coolant back to coolant reservoir but to keep the flow to low by orifice it.

Also noted that vent line connection form crank case and from intermediate cooler is use as ORIFICE to maintain the vent/pressure in system, but also to keep coolant flow to minimum back into coolant reservoir.

You will see in below photos the old vent line. It has very small opening and work as ORIFICE to minimize the flow of coolant.

It is bad design by Mercedes to use cheap plastic tube to maintain the lower flow in vent by restricting flow and keeping pressure down. Why in the world MB engineers used Plastic Tube for Orifice the coolant in this hot turbo charge engine. Bad design by MB. My gardening system tubing is more better quality then this $100K car vent line.

 

Here is photos of fitting that vent line get connected at Crank Case. This is poorly design cheap plastic fitting in crank case. Why not use some metal tube here.

I am disappointed with Mercedes Benz cost cutting strategies on $100K S Class. You can buy better hose fitting from gardening supply store.

 

Here is photos of fitting that vent line get connected at Crank Case. This is poorly design cheap plastic fitting in crank case. Why not use some metal tube here.

I am disappointed with Mercedes Benz cost cutting strategies on $100K S Class. You can buy better hose fitting from gardening supply store.


View attachment 2733064


View attachment 2733065

I just had the same problem on my 2013 S550, looking for these parts now. Everything that was plastic fell apart.

 

New vent line installed. No more leaks. But there are many more plastic low quality tubing in this Turbo Charge engine that will be needed to replace soon.

 

s550hollywood, I understand your pain. I believe Mercedes has been on cost cutting mission, even on high end luxury brand like S Class. That's the reason I would not prefer EQS Electric Mercedes S Class over Tesla Model S, even better S Plaid.

Any how, I like the naturally asperated engines like M273 on earlier S Class, no Turbos. In M278 Twin Turbo sit on low side of the engine create tons of heat that don't go well with plastic parts.

Even on M273 engine, I recently did the Oil Filter Housing to engine gasket and Oil filter housing to Oil cooler gasket, they both leaks and they look bad due to poor design by Mercedes Engineer. You can see in photos, the path that hot engine oil take from engine to oil filter housing and then from oil filter housing to oil cooler create gaskets failure. Mercedes engineers pick the wrong material for gaskets. Imagine on M278, it will be worst.

Photos shows at 160000 miles on mine 2007 Mercedes S-550 M273 engine.