[mrbyteware]

After driving for about 30 minutes my 2018 X3 G01 starts to bubble and leak coolant out of the expansion tank. The temp gauge remains in middle. The coolant temp is around 109C using Autel scanner.

The water pump was recently replaced. I drained the coolant and vacuum filled. Performed the bleed procedure but no luck.

No coolant leaks anywhere other than when it starts to bubble.

No bubbling when I first start the car. Used the blue liquid test to check for head gasket leak, but the fluid never turned yellow

Replaced the expansion tank cover. Checked the coolant system holding pressure fine.

No codes when running diagnostics using Autel scanner.

Any ideas what the issue might be? Could it be the heat management module?

[mattsheng]

I assume you bleed both high and low temp coolant circuits, right? Maybe try running the bleeding procedures with caps off so that air can vent out instead of building pressure in the coolant circuit.

If your vacuum is not powerful enough (need -0.8 to -0.95 bar for 2 min per BMW), there can still be air pockets in your coolant circuits after vacuum fill. The bleeding procedure probably couldn't handle that many air pockets and thus causing the coolant to bubble.

[mrbyteware]

Thanks mattsheng: I completed the low and high circuit bleed as follows with the caps on:

For low temp circuit bleed: With the car in diagnostic mode (hit stop/start 3 times), fan speed low, high temp setting, hold accelerator pedal for 15seconds.

For High temp, same steps as low bleed then started the engine and: Rev engine to 3500/min and hold for 10s, then idle for 30s, repeat rev/idle steps 5 times.

I believe vacuum was powerful enough that the hoses collapsed during vacuum. I used a 150 PSI compressor.

I will redo the bleed cycles with caps off as you suggested to see if it makes a difference. Another post mentioned the Heat Management Module (which I think is like a thermostat) was replaced for a similar issue. Do you suspect it the cause? How to test if it is not defective. No codes related to it or the water pump from scanner

[mattsheng]

mrbyteware The high temp bleeding procedure should be automatic, i.e. no need to rev the engine to 3500 rpm yourself. I posted this procedure in another thread but I will attach it here as well. I did this procedure on my G01 and I can confirm it worked.

A couple of things:

1. Ignore the "Connect battery charger" step
2. After holding the accelerator pedal for at least 10 sec (Step 13), let go of the accelerator pedal and then step on the brake to start engine (Step 14)
3. The bleeding procedure will start automatically after the engine starts and it will take 11 mins
4. During the bleeding procedure, you will see "service function started" on your instrument cluster

high_temp_coolant_bleed.pdf

[freshxdough]

Originally Posted by mattsheng

mrbyteware The high temp bleeding procedure should be automatic, i.e. no need to rev the engine to 3500 rpm yourself. I posted this procedure in another thread but I will attach it here as well. I did this procedure on my G01 and I can confirm it worked.

A couple of things:
Ignore the "Connect battery charger" step
After holding the accelerator pedal for at least 10 sec (Step 13), let go of the accelerator pedal and then step on the brake to start engine (Step 14)
The bleeding procedure will start automatically after the engine starts and it will take 11 mins
During the bleeding procedure, you will see "service function started" on your instrument cluster


Attachment 3050932

Automatic high temp bleeding is only capable on iDrive 7 cars. iDrive 6 cars do not do it automatically.

[mattsheng]

Originally Posted by freshxdough

Automatic high temp bleeding is only capable on iDrive 7 cars. iDrive 6 cars do not do it automatically.

Thank you for catching my mistake! I thought all G01 have the same bleeding procedure but you're right. iDrive 6 cars still have the same high temp circuit bleeding service function but you have to rev the car yourself. See the attached procedure for iDrive 6 cars. 20221209_085728_REP-REP-P-1700039-G01_B48_VIN7-XXXXXXX.pdf

[383vett]

Are you starting out with the coolant level at min when cold?

[mrbyteware]

Thanks @mattsheng for sharing the bleeding procedure. I have already followed the bleeding steps several times but bubbling remains. The only step I couldn't do is open the bleeder screw because my expansion tank does not have one!!. @383vettnnand I keep the coolant level on the midsection of the expansion tank between the up and down facing arrows. This is the level I start the bleeding process and when I start the engine to drive off. Does the coolant level at cold have to be at a different level to avoid the bubbling?

[mattsheng]

Originally Posted by mrbyteware

Thanks @mattsheng for sharing the bleeding procedure. I have already followed the bleeding steps several times but bubbling remains. The only step I couldn't do is open the bleeder screw because my expansion tank does not have one!!. @383vettnnand I keep the coolant level on the midsection of the expansion tank between the up and down facing arrows. This is the level I start the bleeding process and when I start the engine to drive off. Does the coolant level at cold have to be at a different level to avoid the bubbling?

The repair instruction calls for overfilling the high temp expansion tank by 200ml over the max line. That's how the new cars are delivered too. By bubbling, you don't mean boiling right?

[mrbyteware]

Boiling indeed.

[mattsheng]

Are you able to read coolant temp before and after the radiator? Or coolant temp at other locations?

I can think of 2 issues. 1) the heat management module is fine and the issue is with the coolant. The correct coolant shouldn't be boiling at 105C. 2) the coolant is fine but the heat management module isn't. At 105C, the heat management module should open the entire coolant circuit allowing coolant to flow through the radiator. If it's stuck at warm-up phase, i.e. coolant not allowed to flow through the radiator, the coolant can heat up very quickly and starts boiling. If you can measure coolant temp at multiple places, you can see if there is a huge difference in coolant temp at various places.

[mattsheng]

Just thought of another possibilty. If the coolant pump isn't working, which I doubt is the case, then coolant can boil too.

[abbike18]

Does the cooling system build pressure? Are the big lines than run from the block to the radiator more firm once things heat up?

I'm wondering if you aren't sealing properly and the low pressure in the system is reducing the boiling point of the coolant.

[mrbyteware]

The scanner showed 112C for the coolant temp immediately when the boiling started. The big upper and lower hoses are all firm when the boiling begins. The upper hose firms up sooner and gets much hotter than the lower.

Improper sealing would have resulted in a leak somewhere, but no signs of leak until the boiling begins and the coolant escapes the expansion tank.

I am planning on replacing the Heat Management Module this weekend. My DIY skills in this area are limited but will give it a shot.

[mattsheng]

Originally Posted by mrbyteware

The scanner showed 112C for the coolant temp immediately when the boiling started. The big upper and lower hoses are all firm when the boiling begins. The upper hose firms up sooner and gets much hotter than the lower.

Improper sealing would have resulted in a leak somewhere, but no signs of leak until the boiling begins and the coolant escapes the expansion tank.

I am planning on replacing the Heat Management Module this weekend. My DIY skills in this area are limited but will give it a shot.

Hope this repair instruction will help. (I assume you have a 2018 G01 30i) REP-REP-P-1153015-G08_B48_VIN7-XXXXXXX.pdf

[mattsheng]

Originally Posted by mrbyteware

Improper sealing would have resulted in a leak somewhere, but no signs of leak until the boiling begins and the coolant escapes the expansion tank.

I think abbike18 has a good point. Since there is not coolant leaking, it is possible that the expansion tank cap is not sealing properly. Then the coolant circuit cannot build pressure correctly. So it's possible that either the expansion tank deforms during the vacuum fill or the expansion tank cap is faulty. Both will be easy fix before attempting to replace the Heat Management Module. A faulty Heat Management Module will usually throw fault codes.

[AllBlackBimmer]

Could be vent in the cap… replace the cap before throwing a bunch of money and time at parts.

[mrbyteware]

Thanks mattsheng for the instructions. I agree a faulty HMM usually throws codes, but since all other ideas did not work I proceeded with the installation of a new HMM and vacuum filled the coolant. I also completed the coolant bleed process. The coolant level did not drop after the bleed completed.

I had already replaced the expansion tank cap twice thinking as abbike18 suggested, but no luck.

The boiling happens after 30 minutes of driving, will drive to work on Monday and see if problem solved.

[mrbyteware]

After 2 days of driving, no boiling of coolant. This is a good start, but I am cautiously optimistic and may be too soon to judge if replacing the Heat Management Module fixed the coolant boiling issue. I have a scanner connected while driving and collecting live data. The coolant temp did not exceed 112.8C.

I will provide an update after few more days of driving. Thanks to all who helped especially mattsheng for sharing the instructions documents.

[Autobahn1]

Originally Posted by mrbyteware

I will provide an update after few more days of driving. Thanks to all who helped especially mattsheng for sharing the instructions documents.

Having what seems to be the same problem. Dealer suggests that an animal had damaged harness around coolant temp sensor and that car was now "confused." Wants to replace the entire engine harness! Asked to see a picture of the damaged wires and "unfortunately that's not possible" without paying for hours of removing parts, because they allegedly barely saw the damage with a borescope.

mrbyteware : Did you confirm that the heat management module went bad without throwing DTCs?

[abradford07]

Did you ever get your car fixed? What was the solution?

[njscott]

Hi all. Did anybody ever hear if this solved the issue? I have the same exact issue. Changed water pump, cap and tank. Still boiling over on long drives .. is