Tank for Oil Expansion S212 E250 CDI

[WhisperingWillow]

Salutations everyone,

Someone plz assist me. There is oil in the radiator expansion tank of my 2010 S212 E250CDI with 106k miles. When I checked the levels two weeks ago in preparation for my vacation, it most certainly did not. I saw the coolant level alert when I started it up for the first time, and when I looked closer, I saw that it was completely filled with oil. If the oil was the cause of the low coolant level warning, then it had only occurred on the most recent trip.


I had it hauled to the garage since I assumed it was an oil cooler, and they confirmed my suspicions. After beginning to disassemble the components, they discovered that the engine oil was devoid of water, but even more perplexingly, there was no oil in the water tubes around the oil cooler. According to their findings, the oil cooler isn't the culprit.

Since I've only had the vehicle for a year, the mechanics who came to inspect it noted that the oil cooler seemed to be relatively new. So far, they have concluded that the oil cooler is not to blame because neither the oil nor the water in the pipes surrounding it contain any oil.

When they removed the oil from the line that went to the top of the expansion tank—the Bleed line, if you will, according to the drawing that is attached and labeled '250'—a small quantity of oil remained at the end where it connected to the top of the radiator. Instead of entering through it, the oil could have drained back down there if the level had been higher. Because of this, we still have no idea how the oil got here.

Oil in the expansion tank has led them to speculate that it may be transmission oil, a theory with which I disagree. The oil is dark in color, has no emulsion, and flows freely. I would be amazed to see ATF oil that appears healthy and jet black, even when I account for the fact that it darkens with age.

They think the gearbox oil cooler in the radiator has cracked, but I'm not convinced by the jet black color and would value your opinion.

We are now investigating the matter and have temporarily halted the process. The oil cooler can't be the only possible culprit. Possible choices:

Head gasket: I'm not sure, because the expansion tank has an excessive amount of oil. The tank had been filled to the top of the screwcap. Furthermore, there was absolutely no milkiness or emulsion, leading me to believe that it probably is. It ran well as I drove it into the retrieval vehicle, and there was no smoke of any kind.

Is there gearbox oil that looks like that? I don't think so, because it was clean and black when I changed it a few months ago. Six months ago, during an autobox service, the gearbox oil was changed. Is the ATF still behind it?

Is it feasible for a cracked block to let the passage of oil into a water jacket but not the flow of water into oil?

Could there be any other possible reasons? The mechanics have temporarily halted the process because they haven't figured out how to get to the oil cooler—which means the car isn't completely disassembled—but they still have a couple of hours to go before it can be run again.

How can we verify that the gearbox oil is free of contaminants? Unfortunately, we are unable to access the gearbox fluid to assess its condition because the unit is sealed for life and does not appear to have a sump drain or an accessible filler. Can the filled-in pipe be lowered in any way? Is it possible for the black oil in the expansion tank to be ATF?

Do you have any ideas on how we might focus our inquiry to find out what's causing this? Any advice you could provide me would be greatly appreciated. The mechanic is confused and first recommended a top end rebuild before recommending a new gearbox as a remedy. Therefore, I also believe they are unaware of this.

I would greatly appreciate any assistance you can provide.

[Black_raven]

Low compression in two neighboring cylinders is a telltale sign of a blown head gasket, which is typically located at the narrowest point and can be detected using a compression test.

When the engine is turned off, a pressure gauge attached to the cooling system will reveal whether or not the system keeps the pressure. In the event that it doesn't, a leak may be present, potentially affecting the cylinder head.


To gauge the internal pressure, squeeze the top hose of the radiator. To release the pressure, take the radiator cap off (with the engine turned off), replace it, start the engine, and rev it up. The head gasket has blown if the pressure is built up too rapidly; normally, it should do so gently as the engine warms up.

The gadget can detect exhaust gases in the cooling system if you bring the vehicle to a MOT testing site and request that an exhaust gas analyzer be lowered into the expansion bottle, but above the coolant level.
 

[Black_raven]

https://www.amazon.co.uk/Block-Tester-Bt-500-Combustion-Leak/dp/B06VVBSFTF/

[Black_raven]

 

[WhisperingWillow]

The repair shop did claim to have performed a compression test, which confirmed that the gasket around the engine's cylinder head was in good working order.

Given the presence of oil in the coolant, I suspect a leak. Given the current state of the system, I am unsure if it can maintain pressure. Its also pretty much disassembled making further testing hard.


Among the things I find hard to believe is the possibility that the oil is gearbox oil. Its recent oil change gives it a clean, healthy appearance, and its jet black color belies its cleanliness. The gearbox oil, as far as I can tell, is neither black nor green nor greenish-blue. The lack of a dipstick is explained as being due to the unit being "sealed for life," which prevents us from knowing the color of the gearbox oil. But there is a blanked-off ATF dipstick tube that is located to the left of the engine oil. According to my preferred artificial intelligence system (Pi), there is a genuine ATF dipstick available (part number 722589012100). However, when I contacted Mercedes dealers, they declined to sell it to me since it is classified as a "workshop tool." Fortunately, I was able to find it online.

Has anyone used an ATF dipstick on an OM651 / 722.6 before? I'll report back to you on the effectiveness of the Febi Bilstein part match that I ordered. In that case, I'll be able to verify the color of the gearbox oil and determine if it's polluted.

Are you in agreement? Is the gearbox actually made of jet black, virgin oil? My guess is no.

To review, currently:
- The oil color makes me doubt that it's gearbox oil; thus, it isn't gearbox oil cooler. The compression test confirmed that the head gasket surrounding the combustion chambers was fine, but a leak in the gasket connecting the oil and water channels could be the culprit. There may have been a disastrous crack in the block or the skull.

On the other hand, the oil cooler might be the culprit. Given the amount of oil in the coolant, it's strange that any nearby waterways would be spared and clean, but the garage insisted that this wasn't the case because the surrounding waterways weren't polluted. Is it because the car hasn't clogged up any waterways yet, or is it because it just got fresh oil and filter two weeks ago, during which there was clearly no oil in the coolant?

At this point, I must decide whether or not to instruct the garage to proceed with reaching the oil cooler. If it's not the oil cooler or gearbox oil cooler, then taking the cylinder head off for diagnosis is necessary for everything else, right? Upon closer inspection, however, it becomes clear that in order to reach the head gasket, all of the components necessary for the oil cooler must be removed.

I just need to know if the oil in the expansion tank is for the transmission or the engine before I can call the garage.

Am I missing something?

Much obliged.

[Gianni682]

I'm at a loss for suggestions because we've pretty much covered everything.

[Gianni682]

As an aside Because I experienced the same issue with an old dump truck that we used for cleaning out our stables, I can say with certainty that EP gearbox oil does, in fact, emulsify to a cream color when combined with water.
Additionally, while "EP" lubricants are specifically designed for gearboxes, it seems that the majority of normal gearboxes do not operate under pressure. My guess is that if a gearbox had a heat exchanger, the pressurized coolant would exit the cooling system much more quickly than the gearbox lubricant would enter it.

[Gianni682]

A cylinder head failure across the same channels would cause the same symptoms as a crack in the block or cylinder head between the coolant and lubrication channels, in my opinion.Both of those things can go wrong with a cylinder head and it will still be perfectly OK as far as combustion pressure is concerned.

[Gianni682]

Hmm...

Just so you know, I remember hearing something about how the problem of "very old coolant breaking down into an oily mess" might be fixed by simply replacing the coolant. N.B. That information is anecdotal, so I cannot in any way verify it. However, I seem to recall that a cooling system sealant ingredient had previously been used and could have contributed to the symptoms.


Whatever you decide, best of luck, and do report back to us when you have solved the mystery.

[WhisperingWillow]

It's helpful to know that. Curiously, no emulsion is visible. What I mean when I say the expansion tank is full of oil is that it is filled with thick, black stuff that looks like motor oil. There is absolutely no creamy emulsion. This is the main reason why I believe it happened just a little distance before the "check coolant" alert appeared during startup. So far, I've come to the conclusion that the expansion tank is the uppermost section, and that the oil cooler "skimmed off" the oil that floated to the top when it split. We only do short journeys, therefore the engine got switched off. Because of this, the rivers are rather empty. This is just my current best guess, however it could be completely wrong.

[WhisperingWillow]

I understand. Now we know the combustion chambers are fine thanks to the compression test the garage ran, but they didn't mention anything about the oil-water leak or the damaged block or head. Is there a way to examine the water jacket for leaks now that it's mostly disassembled? It could be done by reattaching the water line to the block and then testing the pressure, but then water would leak out of the oil cooler, making it even more difficult to pinpoint the exact location of the leak. In the event that the oil cooler comes up and checks out, the only method to determine is by looking at the head gasket.

[WhisperingWillow]

Since I checked the level two weeks ago and added more, I can say with certainty that the coolant is not old. But it's good to know.

We'll make sure it's not gearbox oil; if that doesn't work, we'll go on to the oil cooler and cross our fingers. In any case, we need to get out of here soon.


I am grateful.

[KOOLCAR]

Definitely, the transmission won't stay sealed forever.

The Mercedes manual specifies how often you should change the filter and fluid. Even if these have evolved, they are still necessary.

[BENZE220AMG]

How long has the car been on the market? Placing oil in the expansion tank is a typical tactic for would-be purchasers looking to lowball sellers.

[WhisperingWillow]

Wow, that's dark! I've never heard of that before, but I can see how it may be useful. Surprising things might happen at any time!

[WhisperingWillow]

In case anyone was wondering, the garage has indeed identified the oil cooler as the source of the problem. Grainy sand filled the space within the water jacket and all the pipes that had been inserted into it when we removed it. Plenty, not just a little. The result is that the cooler has burst due to the buildup of pressure.


From what I can see, it has nothing to do with the engine and is neither magnetic nor metallic. I am familiar with the car's history up to the last year's 30,000 miles, during which time it has had the oil changed and a serpentine belt installed, but other than that, it has been completely unaltered. Nothing has been done with the coolant system.

Is there anybody who can guess what it could be? Although it's strange that it went 30,000 miles before exhibiting difficulties, one reasonable hypothesis is that a radweld similar to Bars Leak may have been added (too many times) prior to my ownership. My only other theory is that someone or something was deliberately added to the coolant system, but nobody other than people I trust has been near the vehicle.

Is anyone else thinking about possible other explanations? I am grateful.