Oil in Expansion Tank S212 E250 CDI

[Chrishazle]

Greetings everyone,

I need assistance, please. My 2010 S212 E250CDI, with 106,000 km, has a radiator expansion tank filled with oil. Two weeks ago, it certainly did not, as I verified the levels before to a trip. I discovered it because, when starting, a coolant level alert appeared for the first time, and upon inspection, it was all oil. If the low coolant level alert was caused by the oil, it occurred just on the previous trip.

My first assumption was an oil cooler issue, prompting me to have it towed to the mechanic, which shared the same opinion. They started removing the components and discovered that, in fact, there was no water in the engine oil; more perplexingly, there was an absence of oil in the water tubes around the oil cooler. Their determination is that the oil cooler is not the issue.

I inspected the automobile, and they said that the oil cooler is rather fresh, despite my ownership of the vehicle for just one year. The current assessment indicates that the oil cooler is unlikely to be the cause, given there is no oil present in the surrounding water pipes, nor is there any water in the oil.

The conduit going to the apex of the expansion tank, referred to as the bleed line in the attached picture labelled '250', was saturated with oil upon disconnection. Conversely, the terminal end connecting to the upper section of the radiator exhibited little oil residue. However, because the oil level exceeded this point, it may have drained back down rather than entering via that location. The origin of the oil remains unknown.

Upon examining the oil in the expansion tank, it has been suggested that it may be gearbox oil; however, I disagree with this assessment. The oil is pitch black, devoid of emulsion, and flows freely. Even accounting for the darkening of ATF oil with time, I would be astonished to see it as jet black and appearing healthy.

They believe the gearbox oil cooler in the radiator may have ruptured; however, due to the jet black colouration, I remain sceptical and would value your opinion.

We have suspended the work while we investigate the issue. What alternatives exist if the oil cooler is not the issue? Choices:

Head gasket: I suspect it is not the issue, since there is a significant amount of oil in the expansion tank. The tank was filled to the screw lid. There was no emulsion or milkiness, leading me to believe it would be otherwise. No smoke of any colour was seen; it operated well while being driven aboard the rescue vehicle.

Gearbox Oil Cooler in Radiator: I doubt it, since it was clean and black (it was replaced a few months ago), but is there gearbox oil that like that? The gearbox oil was replenished during an automatic gearbox service six months ago. Is it still possible for it to be ATF?

Can a block break in such a manner that oil seeps into the water jacket while preventing water from entering the oil?

Are there more possible causes? The garage has halted work as they do not believe the issue is the oil cooler, given that the surrounding pipes are not accessible. The vehicle has not been completely disassembled to reach it, but it will need a few hours to reassemble for operation.

Do you have suggestions for verifying contamination in gearbox oil? As a hermetically sealed machine, there seems to be no sump drain or accessible filler, preventing us from evaluating the condition of the gearbox fluid. Is there a method to lower the sealed filler pipe? Can the oil in the expansion tank be ATF if it appears black?

Can you provide a method to refine the study to ascertain the source of this issue? I would really appreciate any advice you may have. The garage is uncertain and first proposed a top-end overhaul, then recommending a new gearbox. It seems they are also uninformed on this matter.

Any assistance you may provide would be profoundly appreciated.

[bvlenci]

A compression test may reveal a blown head gasket, since failures often occur at the narrowest point, resulting in low compression in two contiguous cylinders.

A pressure gauge installed in the cooling system will indicate if the system retains pressure when the engine is turned off. If it does not, there may be a leak, maybe into the cylinder head.

Compress the upper radiator pipe, then assess the internal pressure. Remove the radiator cap to alleviate pressure (with the engine off), then replace the cap, start the engine, and then increase the RPM. If pressure accumulates rapidly, the head gasket is likely compromised, since pressure should increase gradually during engine warm-up.

When you bring the automobile to a MOT testing facility and request that they insert an exhaust gas analyser into the expansion bottle (ensuring it remains above the coolant level), the apparatus will identify any exhaust gases present in the cooling system.

Alternative methods for verification also exist:

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

[bvlenci]

https://www.lislecorp.com/specialty-tools/combustion-leak-detector

[bvlenci]

 

[Chrishazle]

The garage reported doing a compression test and determined that the cylinder head gasket was intact (or at least the components of the combustion chamber were).

The coolant system seems to have a leak, since it is saturated with oil, indicating a rupture inside the system; thus, it is uncertain if the system can maintain pressure at this time. It is mostly dismantled, complicating further testing.

I find it difficult to accept that the oil could be gearbox oil. The engine oil is jet black and seems clean and healthy, having been recently changed. Based on my understanding, the gearbox oil is either green or greenish-blue, but not black. A basic dipstick would indicate the oil colour in the gearbox; however, as the mechanism is 'sealed for life,' it is said that no dipstick is provided. There exists a dipstick tube for the ATF located to the left of the engine oil, but it is sealed. I learnt via my preferred AI (Pi) that an ATF dipstick with component number 722589012100 exists; however, Mercedes dealers declined to sell it, citing it as a 'workshop tool.' Nonetheless, it is available for purchase online.

Does anybody have experience utilising the ATF dipstick on the OM651 / 722.6 gearbox? I have purchased the Febi Bilstein component and will inform you of its efficacy. If it works, it will enable me to verify the colour of the gearbox oil and ascertain its contamination status.

What is your opinion? Could jet black fresh oil really be gearbox oil? I believe not.

In summary, at this juncture:

- I doubt it is gearbox oil due to the oil's hue (therefore, not from the gearbox oil cooler).
- The head gasket around the combustion chambers is intact based on the compression test; nevertheless, there may be a leak in the gasket between the oil and water passages.
- It may result in a catastrophic fracture of the block or skull.

Nonetheless, it may only be the oil cooler. The garage said that they did not believe the waterways were polluted; but, due to the significant presence of oil in the coolant, it would be unusual for any rivers to remain untainted and clean, since the oil would circulate throughout the engine. The vehicle had a new oil and filter two weeks ago, and there was no oil contamination in the coolant at that time. Given that it has been driven only few kilometres subsequently, it is possible that the waterways have not yet been obstructed.

I must decide whether to instruct the shop to proceed with the oil cooler repair. If it is determined that the issue is neither the oil cooler nor the gearbox oil cooler, I feel that the cylinder head must be removed to examine the remaining components. However, to access the head gasket, all components necessary for reaching the oil cooler must be removed regardless.

I need to ascertain if the oil in the expansion tank is for the transmission or the engine before instructing the service to proceed.

Is this coherent?

Thank you!

[keithmerc220]

For what it's worth Your proposition seems to be somewhat perplexing, jjc2020.
I find it challenging to propose anything that you have not previously addressed.

I can verify that EP gearbox oil emulsifies to a cream hue when combined with water, since I had this issue with an old dumper truck used for cleaning out our stables.
Moreover, although "EP" oils are classified as gearbox oils, to my knowledge, most traditional gearboxes operate without pressurisation. Therefore, it is reasonable to assume that if a heat exchanger were present in a gearbox, the pressurised coolant would exit the cooling system to a far higher degree than the gearbox lubricant would infiltrate the coolant.

[keithmerc220]

I do not see how a fracture in the block or cylinder head between the lubrication and coolant channels would present differently from a cylinder head failure occurring across the same channels. A cylinder head may fail in one or both of those features while maintaining full integrity concerning combustion pressure.

I remember being informed that "aged coolant deteriorates into an oily substance," which was reportedly rectified by just replacing the coolant. If I recall correctly, there was also mention of a cooling system sealant component that had been previously used, and this may have contributed to the condition noted. The information is hearsay; thus, I cannot confirm it in any anyway.

Best of luck; should you uncover the details, please inform us.

[Chrishazle]

Thank you for the excellent answer. I really appreciate it.

That is helpful information. Notably, there is an absence of any emulsion. When I state that the expansion tank is filled with oil, I refer to genuine engine oil, characterised by a viscous and dark appearance. No creamy emulsion whatsoever. This leads me to believe that it happened just a few miles prior to the 'check coolant' alert at beginning. My hypothesis at this juncture is that the oil cooler ruptured, causing the oil to rise and be 'skimmed off' into the uppermost section - the expansion tank. The engine was thereafter turned off as we only do brief trips. Consequently, the waterways are mostly devoid of content. This may be complete rubbish, but it is my most informed conjecture at now.

[Chrishazle]

That is logical. The compression check of the garages confirms the integrity of the combustion chambers; however, it does not address any leaks in the gasket between oil and water, nor does it indicate the presence of a cracked block or head in that area. The assembly is mostly disassembled; is there a method to inspect the water jacket for leaks? It is conceivable to reconnect the water hose to both the inlet and outlet of the block and conduct a pressure test; however, this would also result in leakage via the oil cooler, thereby failing to identify the source of the leak. The only method to ascertain is to visually inspect the head gasket, provided the oil cooler is intact and functioning properly.

The coolant is certainly not old, since I verified the level and replenished it two weeks before. It is beneficial to be informed, however.

We will verify that it is not gearbox oil; if it seems not to be, we will proceed with the oil cooler and hope that is the issue. If unsuccessful, it is time for decapitation.

Thank you!

[alpaco45]

The gearbox is unequivocally not sealed for its entire lifespan.

Mercedes has prescribed times for the replacement of the fluid and filter. These have evolved throughout the years, but they remain mandatory.

[Motoman]

Have you listed the automobile for sale? A prevalent fraud involves prospective purchasers introducing oil into the expansion tank to undervalue the seller's offer.

[Chrishazle]

That is rather ominous. I am unfamiliar with the concept, yet I can see its potential efficacy. Individuals consistently astonish!

[Chrishazle]

The garage has identified the fundamental problem as the oil cooler. Upon removal, all the piping connected to it and the hollow inside the water jacket were filled with granular sand. Not a little amount - a significant quantity. This has resulted in increased pressure, leading to the rupture of the cooler.

Upon inspection, it is neither magnetic nor metallic and resembles no component of the engine. I have driven 30,000 miles in the automobile over the last year, therefore I am familiar with its history for that duration. During this period, it has had an oil change and had the serpentine belt changed; no other maintenance has been performed. There is no functionality in the cooling system whatsoever.

Do you have any recommendations on its potential nature? It is suggested that a radweld product, such as Bars Leak, may have been excessively applied prior to my ownership, which is a plausible theory; nevertheless, it is peculiar that it functioned well for 30,000 miles before the issues arose. The one option I can conceive is that something was intentionally inserted into the coolant system; however, no one has approached the vehicle except for those I trust.

Does anybody have more insights on its potential nature? Thank you.