[Erickuokwa]

Hi! I recently bought a 2018 65k mile x3 m40i and on the drive home, the coolant overflow starts to bubble/boil inside the tank. No modifications or cel.

I had 90day 4000 mile warranty with autonation so I took it into BMW Buena Park dealer and they said it needed tear down approval before they can further diagnose what is wrong.

Should I return the car within my 5 day money back while I can? Or is this a common coolant leak easily fixed.

[cbpip]

Take it back !

[Tejas1836]

Bubbles/fluid coming out of the return line to the tank? If yes, that is normal during warmup

[Erickuokwa]

Update with some good news! they are going to continue the remaining 5 day money back after it comes out of the service department. So I’m able to decide after they pinpoint what is broken. I hope it’s nothing too major as it’s optioned out pretty nice to my liking.

[cbpip]

Make sure someone does an exhaust gas check in radiator. Very simple test. Checks for blown head gaskets. An indie shop can do it cheap.

https://bryansgarage.com/test-coolan...exhaust-gases/

[RockCrusher]

Bubbling is not a good sign. That suggests a head gasket problem that is allowing cylinder compression or power stroke pressure to leak into the cooling system.

In this case as has been offered by cbpip a test can be done for combustion gas compounds in the coolant. Also, the engine oil can be analyzed looking for (among other things) the presence of anti-freeze compounds in the engine oil.

Boiling is a sign the cooling system is not able to maintain pressure which allows hot coolant to boil. This can lead to localized overheating.

For a cooling system that is suspected of a pressure leak I like to perform a hot coolant pressure test.

But you are going to have the shop look into this so I'll not bother to post the hot coolant pressure test procedure. However, shop techs appear to favor a cold pressure test which in my experience often fails to uncover a leak that a hot coolant pressure test uncovers.

But a thorough inspection of the various cooling system leak points can find signs of coolant leakage (often just dried anti-freeze residue). Depends upon how thorough the tech is. Some take the position if there is no leak (cold leak) there is no leak and don't bother with an inspection.

In spite of the above suggestions I agree with cbpip's recommendation to take the vehicle back, take advantage of the 5 day return policy.

While you like the vehicle a rule with used vehicle buying is there is always another vehicle. In the context of this discussion one without bubbling/boiling coolant. (And of course with no other abnormal behavior/symptoms.)

My concern is the shop will find "no problem" and then you accept the vehicle and after the return the vehicle period has expired symptoms will appear. Or the vehicle will be repaired but not completely or there are complications that have arisen from this bubbling/boiling condition.

[rantarM3]

Return that percolator ASAP. Consider that the dealer, during its intake process for the car, failed to (or ignored) this issue. Leads to the question of what other issues they may have failed to identify with this car.