Hey all! 2014 E550 4matic owner located in Chandler, Arizona here.

I recently purchased this vehicle with 120k miles on it and it had nearly $9k in maintenance done back in June. I purchased in November.

I recently developed a coolant leak which I understand is common with these vehicles however the entire system was replaced by Group One Motorwerks in Tucson, Arizona. The leak seems to be coming from the overflow reservoir but I can't entirely tell. The other problem is that I'm getting conflicting information online about the correct coolant for my 2014. Some say the purple and some say the blue. The paperwork from Group One says OEM so that didn't help but the color is bluish/green in my opinion inside the reservoir. Parts store wanted me to buy purple but I held off until I could get some better information. Since the leak started, I have been keeping an eye on everything and when I park in my driveway (at an incline) the next morning I get the "message" to check the coolant level. This message goes away and does not come back if I'm parked on level ground. The leaking is not constant but only after I have driven whether at an incline or not. I have also noticed that the coolant seems to be boiling after driving (even only a handful of miles) but the temp. gauge in the car does not read greater than 90 degrees F.

Here is the work that was done in June by Group One:
-MB A Service 212
-Brake Fluid Flush
-Inspect Turbo Coolant Line to Identify Leak
-Radiator, Oil Cooler, and Drive Belt Replaced
-MB AT Service
-MB 212 Washer Reservoir Leaking - both reservoir and cap replaced (questioning this...)
-Water Pump Replaced
-MB278 Turbo Coolant Leak - All lines/hose assemblies replaced
-Another Coolant line leaking replaced (paperwork does not say which line)

When I purchased it was so clean you could eat off of the entire inside of the engine bay. No visible spray, leaks, residue or anything.

I've attached the images for what I am able to see without taking anything out. My questions are - thoughts on the most likely culprit of this leak (or how since it seems like it may even come out of the cap) and what is the proper OEM coolant I should be using? I know I am a new owner and it has been 6 months since the service but it's less than 2500 miles since that service in June to today - does the shop have any responsibility here? (not really looking to drive to Tucson to get it fixed unless it's more major than swapping out the reservoir.

Thanks in advance for the thoughts! I really enjoy working on my cars... I drove a 1972 Chevy El Camino 50 miles a day for over 2 years straight! Not afraid to get dirty.

Cheers!



Notice residue around the cap and the lip of the top half.


Some Spray next to the reservoir

Some sort of residue built up on the bottom of the reservoir but looks dry and may have been much longer.


Only area up top that I can see has some sort of wet spots. Reservoir side closest to the motor

The hole it is dripping out from onto the ground when parked on flat surface or incline.


Inside the cap. Color seems Blue and not the purple the part store is trying to give me.

 

You did good by not listening to the purple advice- This cooling system uses Blue/Turquoise chemistry.

Being in high heat AZ region you need your cooling circuit in good repair.


3x classics

You can use a UV dye to spot exactly your leak source or replace : the plastic expansion tank + Cap + hose/O-ring as these 3 are know to have limited service life.

As to the source of high heat: its from the partly dry cylinders below 3500.Rpm.
Bump up your summer oil to 10W50 that will actually provide a decent W40 viscosity film under high heat.
There is a coolant pump mod that consist in running the electric coolant pump at all time to lower heat. Turbo ppl report positive improvement.


The heat management in this car is a little bit on the limited side even with everything working "normal".
I find having the radiator fan running in winter borderline odd. I too am missing some answers on heat management regardless of managed-thermostat. Like the coolant temp sensor reference is skewed/lying to ECU.

The N01 killer is the fragile plastic coolant adapter located at engine rear towards the firewall. There sre couple plastics + rubbers that need preventative renewal.


@S-Prihadi keeps his turbo cooling pipes under close watch for goood reasons!!

 

thanks for the clarification on the coolant type! Any brand you recommend or I should stay away from? I know O’Reilly’s has an “OEM” blue European coolant.

I will definitely check on the dyes to see if I can find the exact location of the leak. I did just learn that someone else cleaned the cap really well and it stopped leaking but that seems a bit odd.

I know these are all known for failing but sort of bummed that it’s less than 6 months since it’s all been replaced and having these issues. I’ve only been driving it for 3 weeks now and it hasn’t been too hot here but I have been driving it every day.

thanks for the advice on the advanced cooling options as well! I’ll dig into that before our spring rolls around and we jump back into the 90’s!

wish there were some aftermarket support options that were bulletproof fixes. Seems like an opportunity with so many having the same issues and so many of these on the road?

Cheers!

 

My 3.5NA has always smelled and leaked coolant from the first day and the first mile, seriously! Don't bit yourself up unless it's a productive leak that really dumps out (UV dye).

Just recently near 50KMi it has stopped burning oil and smelling coolant.


leaky cap

Your pics show an active leak at the cap... thing is once pressure is well sealed in something else going to get stressed out.
We know the cap is supposed to vent and the plastic tank is not supposed to split but regardless that's what happens.
Given you're in a heat stressed area, your best be proactive instead of wait-N-see.

The issue is normally even the cap is not supposed to safety-vent under standard conditions. The car produces too much heat that's poorly removed.

I wonder if these smart-thermostats are worthless or the main pump is ultra undersized to be useless - I get it, the ECU runs these engines a little warmers but radiator fan and venting through open cap under normal conditions is not too impressive.


+++ internal vent:
I think the cap has an internal venting path through the tank.

 

On my third M278 car and I live here in the valley in AZ as well. Looks like the leaking coolant is pooling onto one of your lower control arms. Had the same issue on my W222 S550 just a week or two ago. Found a leak behind the firewell just below the font cowl. There are a number of lines back there along with the heater control valve (I believe this is this case on your car as well). Found a leaky line along with a leaky heater control valve. Took me an afternoon but its not the worst job. I would check there and see if you see some old, caked up coolant behind the engine from the top.

 

I will definitely look at this. I’m hoping it’s simple since the entire system was just redone and just want to fix it haha especially before any more hot days arrive for us.

where are you grabbing your parts in the valley? I’m down in Ahwatukee.

 

So according to your first post on what has been done it looks like the all of the turbo coolant lines were replaced, but not the entire cooling system. This isn't the worst thing in the world as the turbo coolant lines on the M278 will pretty much always leak at some point, so good thing they're done. I'd definitely look at what I had suggested as the heater control valve leaking can be a common thing as well.

I'll PM you about parts.

 

Use 326.0 or 325.0 coolant for your M278.
Simple explanation : 325.0 = Concentrated 100% coolant and the 326.0 = Pre-Mixed 50/50 coolant and proper distilled water
https://mbworld.org/forums/e-class-w...formation.html


The 1.4 BAR pressure cap and the coolant reservoir works like this :
01. When 1.4 BAR is reached, the pressure cap internal sealing system will rise up a bit and allow the overflowing coolant to go to small hole A and dumped to bottom of the reservoir at hole B. A & B are interconnected.

This is also to protect us the user from getting hot coolant spray when opening the pressure cap while coolant is hot, with doing counter clockwise rotation a tiny bit like 90 degrees or so ...and let the gassing off or overflow to occur to A and B holes.



02. You best replace your coolant cap, it might be weakening already, because the "leak" or venting is up to the red arrow zone below, where by right hole A would manage it nicely.



Attached spec of the cooling circuit and the pressure cap. 2 pdf


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The pressure cap looks simple but it is not that simple, when you are done reading COOLANT PRESSURE CAP TEST VALUE.





Buy genuine coolant pressure cap please.



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There are 2 types of cooling system on M278 that I know of.
1st is the turbo aftercooler cooling is shared with the engine cooling circuit and the dead give away is that the coolant reservoir bottle is only 1, that big black top one as per your photo.
2nd one is a totally separated turbo aftercooler cooling ( like my Turbo 3.0 M276 ), where there is a smaller white color coolant reservoir bottle at middle of engine front.
Which version is yours ?


2nd version

 

Agree with all of the above. In case you have not tried this yet: From above, you can double twist-tie small pieces of paper towel to (not hot) coolant lines to try to narrow down leak source(s). In my case "3" was the first problem, the 'Y' junction a little farther down (not in photo) was my second problem. The cap "2" does not appear aligned. Everything in a Benz is aligned . Check that it sits/clicks/aligns properly. also, From Below, you can temporarily remove the under-panels for several calm weather days (no high wind, no sand storms, no rain) and place clean, uniform paper in your garage parking spot to locate drip locations more accurately. btw, I think that is 90C as a temp. In winter or summer - my gauge never moves. There is a thread somewhere that discusses the micro-accuracy of this gauge. I am surprised at "coolant boiling". AFAIK, the point of coolant is NOT to boil, assuming the mixture % is correct. Boiling would mean air in the system which leads to a ineffective or non-working system depending upon other factors. Car looks great. Congrats.

 

Peak makes OEM coolant in the US, also make sure your not overfilling, that could be the leak issue

 

Couple of updates.

Noticed today that my fan is not kicking on even after driving for some time or sitting idle for 5+ minutes.

Back behind the motor looks clean. No signs of leaks there. It all seems isolated to the area around the reservoir.

additionally this part “runs” or “hums” for about 5 minutes after I’ve parked and turned the vehicle off.

Thoughts on the fan or this thing?

cheers!


This is the part that “hums” for a while after parked. Also seems slightly out of place but I’m not sure if that’s normal.

 

That is the small black bosch pump is the HVAC heater core assisting circulation pump.

Get a scanner and read the fan command %. If now in December your region is cold and you run above 50MPH, fan may not kicked is not unusual.

 

I'll trade you!!

Your fan is lazy while my is doing overtime - The one thing though s my engine packs less heat now than it used to when oil was getting vaporized out.

I heard my little electric pump the other day after stopping my engine.

I am growing more confident Tstat operation is impacted by overheated plastics. Conveniently stuck in a median half way position neither shut nor wide open. Perfectly poor circulation to heat stress weak parts unless you know how to recognize poor cooling signs.

Sanity check: when fan is commanded to run then Tstat opening duty better be maxed out (reverse ECU logic reads 0% PWM for full open, true?)

 

Some cars do have the aux coolant pump running after shut-down to even-up "hot spots" on the engine and this is normal.
Do you have a scanner you can use for monitoring temperature while driving?
The dash temp gauge is dummy gauge and what you see might be simply result of overheating.