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BMW E46 318ti Query: Disconnecting Water Hoses from N42B20 Oil Cooler - Possible?

mavi 11232 14
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  • #1 16947343
    mavi
    Level 19  
    Posts: 493
    Rate: 41
    BMW E46 318ti Query: Disconnecting Water Hoses from N42B20 Oil Cooler - Possible?
    Hello

    I am aggravating the problem in my engine with water constantly getting into the oil. Despite the quite obvious answer, which is the high probability of damage to the head gasket, the mechanic, diagnosing the operation of the engine, still does not believe that it was a head gasket. The engine runs smooth, quiet and keeps the engine temperature constant.
    Talking by chance with another mechanic, I found out that corrosion of the aluminum walls in the oil cooler is something common, at least in diesel engines. There are small perforations there and this is often the reason why oil and water mix.
    And now my question is, can I disconnect the water hoses from the oil cooler and connect them together to keep the circuit closed and thus eliminate the cooler?

    The photo shows something like a knob. I understand that this is a valve on the main circuit and turning it off will stop all the oil from flowing through the engine or will it just bypass the oil filter?
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  • #2 16947647
    Anonymous
    Anonymous  
  • #3 16947719
    mavi
    Level 19  
    Posts: 493
    Rate: 41
    And did I write somewhere that it is mounted so-so? She is well aware of its tasks.
    As for the oil overheating, I don't want to bypass the oil cooler and drive this car onto the highway in the summer. Now I am reminiscent of winter, and I am going to drive the car in traffic jams and the oil temperature in such a situation. I do not know any other way to check the tightness of a non-dismountable element. This solution would be for a few days to observe whether the residual water in the oil will evaporate and the car will stop smoking steam from the exhaust pipe and thus eliminate or not the oil cooler.
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  • #4 16947794
    helmud7543
    Level 43  
    Posts: 12618
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    I would change the oil - if it is possible, of course - you don't know how much fluid there is in the oil. Keep the oil at the maximum level - the more it is, the lower the risk of overheating.

    Low air temperature will have little effect on the oil temperature limit. Not a problem on short journeys, and you can overheat even in winter on longer journeys. Do you have a working oil level sensor (responsible for the yellow oil light)? Because he actually monitors overheating, so some protection would be - you get a light and stop without damaging the engine.

    The indicator light on the route - add oil immediately. You can drive some of them at a limited speed.
    The light on after the engine is turned off - add oil at the earliest opportunity.
    That's what the manual says

    The indicator light is on immediately after starting the cold engine - sensor pad.

    The car will not stop smoking with the current aura, so you will not check this way.
  • #5 16947800
    Anonymous
    Anonymous  
  • #6 16950928
    Cobrat
    Level 22  
    Posts: 428
    Help: 35
    Rate: 499
    Dear author, please specify: do you have water in oil or oil in water? Because it's a big difference ...
  • #7 16953874
    RobertLodz09
    Level 30  
    Posts: 1216
    Help: 123
    Rate: 540
    Cobrat wrote:
    author, please specify: do you have water in oil or oil in water?

    After all, the author wrote at the very beginning ...
    mavi wrote:
    I am aggravating the problem in my engine with water constantly getting into the oil.
  • #8 16954767
    mavi
    Level 19  
    Posts: 493
    Rate: 41
    This is how water seeps into oil. There is still quite a lot of steam coming from the exhaust pipe, and when I drive it on a cork or a dipstick it gets so-called. delicate mayonnaise.
    Besides, the engine is running normally; even and quiet and keeps the temperature evenly. On average, I have to add a liter of fluid to the cooling system every 300 km, and there are no water leaks to the outside. The engine was inspected three times very carefully.
  • #9 16954830
    sylweksylwina
    Moderator of Computers service  
    Posts: 13170
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    Maybe it's the head gasket.

    One cannot deduce much from the photos, as it has been written before: it is disassembled and checked.
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  • #10 16955361
    Cobrat
    Level 22  
    Posts: 428
    Help: 35
    Rate: 499
    RobertLodz09 wrote:
    Cobrat wrote:
    author, please specify: do you have water in oil or oil in water?

    After all, the author wrote at the very beginning ...
    mavi wrote:
    I am aggravating the problem in my engine with water constantly getting into the oil.


    Do you have eyes or have they fallen out? The topic of the thread is: "... mixing oil with water", in the first sentence it says: "... water getting into the oil", so please clarify, because there can be both water in oil and oil in water, means something else (as you know), and people treat statements interchangeably !!! Better, however, just to screw yourself and get 2 points, report back ;) .

    @mavi "Cap" for the photo, the head to be checked properly and do not drive like this, you have poor lubrication ...
  • #11 16955379
    robokop
    VIP Meritorious for electroda.pl  
    Posts: 29406
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    Not necessarily a gasket - BMW is famous for cracking heads. So there may be surprise and costs.
    mavi wrote:
    The photo shows something like a knob. I understand that this is a valve on the main circuit and turning it off will stop all the oil from flowing through the engine or will it just bypass the oil filter?
    Close the hatch immediately and never look there yourself again. This is not a valve, just a vent.
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  • #12 16955401
    Cobrat
    Level 22  
    Posts: 428
    Help: 35
    Rate: 499
    And come on with the oil cooler, you'd have oil in the tank.
  • #13 16978748
    blurow
    Level 13  
    Posts: 54
    Help: 4
    Rate: 48
    [quote = "Cobrat"] And come on with the oil cooler, you would have oil in the tank. [/ quote
    cobrat writes well.
    and test the gases in the system cooling, a great patent, and then only the head gasket ...
  • #14 17014916
    Coolbit
    Level 18  
    Posts: 403
    Help: 16
    Rate: 90
    Check the fan and replace the O-ring between the filter and the cooler to be sure. it gets tough over time.
  • #15 17014954
    Strumien swiadomosci swia
    Level 43  
    Posts: 27411
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    Rate: 6379
    This is a faulty valvetronik engine, everything can kneel in a moment, of course, you can bypass the oil coolers, of course, you can remove the heads and make a new gasket.
    I do not know what you are counting on, get to work and collect for repairs and do not click on the forum here and on others.
    What tempted you to buy these padacas were you hungover or did your friend persuade you?
    .
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Topic summary

✨ The discussion revolves around a BMW E46 318ti experiencing water contamination in the engine oil, likely due to a failing head gasket or corrosion in the oil cooler. The original poster seeks advice on the feasibility of disconnecting the water hoses from the oil cooler to temporarily bypass it and observe if the issue resolves. Responses highlight the risks of oil overheating and potential engine damage if the oil cooler is bypassed. Several contributors suggest that the problem could stem from various sources, including the head gasket or cracks in the engine block, and emphasize the importance of thorough diagnostics, including pressure testing and checking for leaks. The need for proper oil maintenance and monitoring is also discussed, along with the suggestion to replace seals and O-rings to prevent leaks.
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FAQ

TL;DR: Owner reports losing 1 liter of coolant every 300 km; “engine runs evenly and quietly.” Likely head/gasket or cracked head, not a valve. [Elektroda, mavi, post #16954767]

Why it matters: This FAQ helps BMW E46 318ti (N42B20) owners diagnose oil–coolant mixing safely and decide next repair steps.

Quick Facts

Can I disconnect the coolant hoses from the N42 oil cooler to test it?

Avoid bypassing the cooler for driving. It increases oil temperature and reduces lubrication, risking seizure. If you must test, restrict it to a brief, static diagnostic, then restore normal flow. “Oil overheating will reduce engine lubrication.” Use a bench leak test to confirm cooler integrity. [Elektroda, 762302, post #16947647]

Is that round “knob” on the oil filter housing a shutoff valve?

No. It’s a vent, not a valve. Do not turn or tamper with it while troubleshooting. Misusing it can introduce air, worsen lubrication, and mislead diagnosis. “This is not a valve, just a vent.” [Elektroda, robokop, post #16955379]

I lose about 1 liter per 300 km and see dipstick mayonnaise—what does it indicate?

Coolant is entering the oil. Common sources are a failed head gasket or a cracked head on the N42. Continued driving degrades lubrication and bearings. Park the car, change the oil, and diagnose before further use. The owner in-thread added ~1 L/300 km with steam and mayonnaise. [Elektroda, mavi, post #16954767]

Could the oil cooler be the culprit if I have water in oil but no oil in coolant?

Less likely. A cooler core perforation typically sends oil into coolant because oil pressure is higher. In the thread, responders point instead to head/gasket issues for water-in-oil cases. Confirm with a combustion-gas test in the coolant and a bench test of the cooler. [Elektroda, blurow, post #16978748]

What’s the safest short-term step if coolant has contaminated my oil?

Change the oil and filter immediately to restore lubrication. Keep the oil at the max mark to reduce overheating risk until proper diagnosis. Do not road-test hard or long. Watch the oil level/overheat warning behavior as a minimal safeguard. [Elektroda, helmud7543, post #16947794]

How do I quickly check for a head-gasket leak on my N42?

Do a combustion-gas (CO₂) test at the expansion tank. 1) Warm engine fully. 2) Use a block-tester fluid per kit directions. 3) Color change indicates combustion gases in coolant, supporting a head/gasket fault. Follow with teardown confirmation. [Elektroda, blurow, post #16978748]

What’s an oil cooler and why is it tied to the cooling system?

The oil cooler uses engine coolant to stabilize oil temperature, preserving viscosity and lubrication. Removing it from the circuit raises oil temps and can precipitate failure, even in winter queues. That’s why bypassing it isn’t recommended for driving. [Elektroda, 762302, post #16947647]

Could an N42 cylinder head crack instead of the gasket failing?

Yes. Experienced members note BMW heads can crack, producing oil–coolant cross‑contamination. A pressure test and inspection during teardown confirm the fault. Plan for higher repair cost if a crack is found. “BMW is famous for cracking heads.” [Elektroda, robokop, post #16955379]

Is there a simple part to replace before tearing down the head?

Yes. Replace the O‑ring between the oil filter housing and the cooler. It hardens over time and can cause leaks. It’s inexpensive and quick, and helps rule out an external-path issue before major work. [Elektroda, Coolbit, post #17014916]

What’s the professional way to verify if the cooler core is leaking internally?

Remove the cooler and perform a sealed bench leak test. Shop rigs pressurize and isolate the oil and coolant passages to detect cross‑leaks. Visual checks alone won’t confirm integrity. “The only thing that can be checked is disassembly and leakage test on a workbench.” [Elektroda, 762302, post #16947800]

Why doesn’t winter weather protect me from oil overheating if I bypass the cooler?

Low ambient temperature barely offsets oil’s heat under load or extended idling. Even in winter, longer runs can overheat oil without cooling. Short trips might seem fine, but it’s a trap for the next long drive. [Elektroda, helmud7543, post #16947794]

My engine runs smoothly and holds temperature—can it still have a bad head gasket?

Yes. Smooth running and normal coolant gauge do not exclude a head/gasket leak. Oil–coolant mixing plus steam and repeated top‑ups strongly suggest internal leakage. Proceed with a gas test and teardown if positive. [Elektroda, mavi, post #16954767]

What is an OBD oil level/temperature warning trying to tell me here?

On this platform, the yellow oil light behavior can indicate low level or high temperature after events. If it lights on route, add oil and drive gently; lit after shutdown means add soon. Treat any alert seriously during contamination events. [Elektroda, helmud7543, post #16947794]

How-To: perform a safe, minimal diagnostic without driving hard

  1. Change oil and filter to remove coolant-contaminated lubricant. 2. Perform a coolant CO₂ test at the expansion tank. 3. If positive, schedule head removal; if negative, bench-test the oil cooler before further road use. [Elektroda, blurow, post #16978748]

Edge case: Can a small leak self-clear after short trips and oil changes?

No. Moisture may evaporate on short trips, masking symptoms, but the underlying breach persists. Continuing to drive risks bearing damage and cam wear. Do not delay definitive testing and repair. [Elektroda, helmud7543, post #16947794]

Bottom line—should I drive while diagnosing oil–coolant mixing?

No. Multiple responders advise against continued driving because lubrication is compromised. Park it, refresh oil, test for combustion gases, and prepare for head work if indicated. “Do not drive like this.” [Elektroda, Cobrat, post #16955361]
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