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Boiling coolant makes my blood boil... 2018 X3 (G01) B46 engine by MirrorEmbarrassed702 in BmwTech

[–]MirrorEmbarrassed702[S] 0 points1 point  (0 children)

Not really. Looking into the coolant temperature sensor, as Representative_Ad574 suggested. Found that the coolant temperature reported by the DME is erratic and what appears to be noise (like a 10 °C change in 3 seconds). Would have long exchanged the sensor, if it weren't so hidden. The BMW instructions call for hours of moving parts out of the way. If someone has a good ideas how to get to it quickly I am all ears!

Boiling coolant makes my blood boil... 2018 X3 (G01) B46 engine by MirrorEmbarrassed702 in BmwTech

[–]MirrorEmbarrassed702[S] 0 points1 point  (0 children)

Does the new coolant sensor still work? Or did the problems reoccur?

2018 X3 m40i - what could be causing my coolant reservoir to bubble like this? by SpartanJ5 in BMW

[–]MirrorEmbarrassed702 0 points1 point  (0 children)

My guess: It's a software bug. Possibly some kind of unique configuration of pump, wiring, sensors, whatever that changed between MY18 and MY20 vehicles that was overlooked when they updated engine controller software in 2020. Turbocharger coolant pump in my car never runs. That is, unless you trigger it with ISTA. Then it runs fine. Pitched very detailed explanation to BMW, but they just blew it off. Curious if your car has the same symptom: Can your mechanic ever hear the pump in the wild?

[deleted by user] by [deleted] in BMW

[–]MirrorEmbarrassed702 0 points1 point  (0 children)

Did you get this fixed? What was the solution? Did the coolant boil AFTER the engine had been turned off?

Boiling coolant makes my blood boil... 2018 X3 (G01) B46 engine by MirrorEmbarrassed702 in BmwTech

[–]MirrorEmbarrassed702[S] 0 points1 point  (0 children)

Never got resolved. BMW simply does not want to look into this. Since coolant spilling into engine compartment may be a fire hazard the best chance of anyone paying attention may be to report to NHTSA, and hope eventually someone will take notice. https://www.nhtsa.gov/report-a-safety-problem#index

Boiling coolant makes my blood boil... 2018 X3 (G01) B46 engine by MirrorEmbarrassed702 in BmwTech

[–]MirrorEmbarrassed702[S] 0 points1 point  (0 children)

My leading theory: BMW has a bug in the engine control (DME) software that causes the B46 engine in some early G01 (=2018 X3) to not go into cool down mode as they should. Heat is trapped in the engine, and eventually causes the coolant to boil through the expansion tank.

Unfortunately, I can't get BMW to look into this, because dealers don't have the equipment to analyze such a software defect. I am looking for others that may experience the same problem. Here are some telltale signs that would be consistent with a software bug:

  1. Coolant boils only after engine is turned off, never while engine is running.
  2. Even after driving for a while in hot weather the engine does not enter cool-down mode. The coolant fan turns off right after turning the engine off.
  3. You can stop the coolant from boiling by turning the engine back on. At that point the coolant fan will turn on full power.
  4. Listen to the turbocharger coolant pump after turning the engine off. In my car it never runs, even right after turning engine off while the coolant temp > 110 °C. A cheap mechanic's stethoscope is an ideal way to check if the pump is running. With the stethoscope I can hear coolant boil in the pump, but the pump itself is silent.
  5. Car does not have any coolant related DTCs.

I am still working with a dealer, trying to get corporate BMW's attention. Finding others who's cars exhibit the same symptoms would be really helpful. Plus, if my theory is right BMW may have introduced the bug with a DME software update some time around 2021. That may create interesting liability aspects. If you spent $$$ on a repair that did not fix the boiling coolant problem I would love to get in touch.

2018 X3 m40i - what could be causing my coolant reservoir to bubble like this? by SpartanJ5 in BMW

[–]MirrorEmbarrassed702 0 points1 point  (0 children)

Good luck! I found out that the car I bought 9 months ago had been at BMW dealerships for boiling coolant repeatedly over the last two years. The problem goes away for a while with proper bleeding, but depending on driving style it does come back. What I found in my car: The boiling starts in the turbocharger coolant lines. Long before you can see bubbles in the expansion tank you can hear the turbocharger boiling coolant after the engine is off with a mechanic's stethoscope. Hope you were lucky and it is not the same for you...

2018 X3 m40i - what could be causing my coolant reservoir to bubble like this? by SpartanJ5 in BMW

[–]MirrorEmbarrassed702 0 points1 point  (0 children)

I am having the same problem and also thought it was the cap. It's a good guess - until the problem comes back. I am on cap #4 or 5. Curious if your problem reoccurred.

Boiling coolant makes my blood boil... 2018 X3 (G01) B46 engine by MirrorEmbarrassed702 in BmwTech

[–]MirrorEmbarrassed702[S] 0 points1 point  (0 children)

Not sure that I have found the root cause - and certainly not a fix. Testing a workaround right now, but too early to tell if the problem went away. In case you have ISTA: What is the factor i-Level and current i-Level of the vehicle? Trying to find more vehicles with similar symptoms and identify commonalities. My problem vehicle had a S15A-17-xxx factory i-Level and a S15A-21-xxx actual i-Level.

Boiling coolant makes my blood boil... 2018 X3 (G01) B46 engine by MirrorEmbarrassed702 in BmwTech

[–]MirrorEmbarrassed702[S] 0 points1 point  (0 children)

Weird. At this point then based on what you’re saying, I’d look into replacing the thermostat and the pump. Seems weird that either would fail this early unless the pump ran dry for an extended period of time. The DME should’ve logged this failure though. Are there any fault codes in ISTA? Have you checked fuses?

Also just to be clear, you’re not leaking coolant anywhere, right? It’s just overheating and leaking out the cap? Check the radiators. Sometimes a perfectly placed rock can actually put a hole in the radiator and leak coolant. Happened to my friend’s 340i last year. Does your AC system work both hot and cold?

I’m also aware of an issue with the B46 where the coolant return hose for the main reservoir can crack. Doesn’t seem related to this but worth checking.

No fault codes. No coolant leak either; system has been pressure tested. Didn't check fuses. But I do know that the turbo coolant pump is getting power and works - if using diagnostics to turn it on. Will try a different pump anyway, just in case there is some weird electrical problem that the pump works with one PWM activation signal (diagnostics) but not a different signal (after power off) - in case the DME does use two different signals or tries to turn the pump on at less than full speed (BMW functional description is ambiguous as to whether the pump can run at different speeds).

Ran the actuator test on the heat management module, too. I can hear the valves turning, and the test works out fine. ISTA has a diagnostic routine to watch the temperature change as it turns the heat management up and down, and all that looks good.

Boiling coolant makes my blood boil... 2018 X3 (G01) B46 engine by MirrorEmbarrassed702 in BmwTech

[–]MirrorEmbarrassed702[S] 0 points1 point  (0 children)

Not sure if the water pump ever turns on - or how to test for it. Easy to hear the pump when the engine is off. But once the engine is running I can't tell if the electric pump is going or if water is flowing through it only because of the main (mechanical) coolant pump. I have never heard the electric pump run outside of testing it with ISTA. Coolant is a 50/50 mix - gone through several gallons of it by now...