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Possible Coolant Leak - W212 65 reg OM651 engine - Suspected Head Gasket Issue?


WannaVulture

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Greetings, everyone.
I'm seeking clarification or insight from someone.

Approximately three weeks ago, the engine coolant indicator illuminated on my vehicle's dashboard. Without giving it any consideration, I proceeded to fill it completely. Following about one hour of driving, the following day, I saw the reemergence of the coolant indicator.
Due to my regular mechanic's high workload, I conducted online research and opted to locate the leak independently by using a Green dye and UV light. Nevertheless, I discovered nothing. Subsequently, I brought the vehicle to a shop where the mechanic conducted a pressure test and confirmed that my coolant system was functioning properly without any leaks. After inspecting the engine oil, he saw that it was not completely black as expected. He noted that the oil had a thin consistency and concluded that the head gasket had failed. Although I have little information about vehicles, he said that the most prevalent indication of a failing head gasket is the presence of white substance surrounding the engine oil cap. However, I have not seen any such white substance. Subsequently, I brought the vehicle to a different garage, where the mechanic said that he cannot definitively exclude the possibility of the head gasket failing, but he is not completely certain.
There are no apparent indications of water leakage in the engine, but it seems to be dissipating or being directed elsewhere.

I am reluctant to invest a significant amount of money on repairing the head gasket, just to discover that the issue remains unresolved.
Do you have any hypotheses on the cause of this problem?
The heater and air conditioning system are functioning well, and the engine is not experiencing overheating, despite a loss of coolant. However, this is contingent upon around 45 minutes of travel.
I do not see any discernible decrease in power either.

The coolant loss amounts to around 0.25 litres after driving for approximately 45 minutes.

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Inspect the water pump for any signs of leakage.
Is there any coolant leaking from the vehicle after parking?
Furthermore, after the temperature has reached the desired level, carefully examine the plastic coolant filling container.
My item had a little puncture that was not noticeable until the coolant swelled and forcefully discharged. Invisible during engine's cold state.

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I recently unscrewed the expansion vessel top to inspect the coolant level, which I had previously replenished earlier in the day. Upon unscrewing, I saw the water level rapidly decreasing before my eyes, accompanied by the distinct sound often associated with a partly clogged kitchen sink. Subsequently, I relocated the vehicle to ascertain the presence of moisture on the ground, only to discover that it was completely dry.

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I have reexamined the matter. I purchased a pressure tester of this kind, and it seemed to function fairly well. I attached the pressure tester and raised the pressure to 20 psi. I saw a prompt but gradual decrease in pressure. After thoroughly inspecting all the locations listed before, I anticipated the presence of coolant being forcefully expelled from a specific area, but I saw no such occurrence. After adding dye to the coolant, I used a UV torch to inspect for leaks. The most noticeable area where a leak seems to be occurring is at a pipe connecting to the EGR cooler. Kindly review the attached photographs. In addition, I have captured photographs of many locations exhibiting apparent dye presence.

Evidently, there is a mixture of water and oil, as shown by the oil level exceeding the maximum limit when I removed the dipstick. Nevertheless, the viscosity of the oil does not enough account for the quantity of coolant that is being lost.

It is worth mentioning that when driving over bumps, I can audibly perceive swishing noises, seemingly originating from the dashboard. I am uncertain if this indicates the movement of coolant inside the unoccupied sections of the cooling system.

The shot above shows holes where oil has accumulated, indicated by yellow arrows. These holes also seem to contain dye, which is visible under UV light since it has a glowing effect.

I would much appreciate any guidance or recommendations.

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Some of the N55 BMW oil coolers may have this problem as a result of a seal failure. I am uncertain about the specifics of your cooler, but it may be worth investigating if this might be a potential issue.

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Thus far, I have consulted two garages and a Mercedes technician about the car's problem. However, none of them have been able to definitively determine the issue because to its uncommon nature, since the typical indication of mayo behind the oil cap is absent. Regardless of the problem, it is evident that water is really becoming mixed with the engine oil. However, the method by which it is infiltrating remains unknown. It seems to be a situation where fixing the head gasket is necessary in order to determine if the issue is remedied. I have reservations about this option due to its substantial cost and lack of assurance that it would resolve the issue.

A week ago, I replenished the coolant in my vehicle but did not drive it. I anticipated that the coolant level would stay same, but to my surprise, the tank was almost depleted. Initially, I believed that the issue was limited to coolant loss while driving, which then evaporated.

Does anybody else have any other suggestions on the potential cause of the problem, or should I go with the head gasket repair?

 Do you know the precise location of the oil cooler?

Does the oil filter/housing have a pathway that allows coolant to leak?

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This indicates the presence of oil seeping into the coolant. However, it is plausible that the reverse may also occur, with coolant infiltrating the oil. It may be more cost-effective to have this possibility investigated.

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