[M5FirstEdition]

The car has only 11,000 miles on it. I took it to 2 different dealerships last week and they didn't believe it's a common issue for this platform. They simply brushed it off and said this perhaps this happens in hot climates like Arizona and California.

Anyhow, After spending days reading about the issue I decided to change the cap and see if the issue still persists.
I can also confirm that the caps between the old and new design are slightly different when it comes the quality of material. See photos.

The cap on the right is the new one.
Execuse my ignorance in using this format. I am new to the forum.

[pbonsalb]

Sure looks like either the cap failed or too much pressure from either too high coolant temp or the tank being over full. A scan tool can give you coolant temp readings. Maybe there is a menu in the idrive or dash but I don’t know how to access it. The standard dash temp gauge is for oil. Even if the engine temp sensor reads low, it is possible the tank is heating up from the turbo and cat under it. An infrared temp gun reading on a hit day after a hard drive might be interesting. Heat also causes expansion. Maybe it is best to keep the coolant level at the minimum level, checking when cold, rather than the maximum.

[M5FirstEdition]

Originally Posted by pbonsalb

Sure looks like either the cap failed or too much pressure from either too high coolant temp or the tank being over full. A scan tool can give you coolant temp readings. Maybe there is a menu in the idrive or dash but I don’t know how to access it. The standard dash temp gauge is for oil. Even if the engine temp sensor reads low, it is possible the tank is heating up from the turbo and cat under it. An infrared temp gun reading on a hit day after a hard drive might be interesting. Heat also causes expansion. Maybe it is best to keep the coolant level at the minimum level, checking when cold, rather than the maximum.

Thanks, I use bimmer link app to check coolant temperature and I am never above 90° (Celsius). Do you think I should take some coolant out? Or just see the effect of the new cap?

[pbonsalb]

I’d wait and watch. Maybe use an infra red gun on the tank to see how closely it matches what you see on the scan tool.

[logicators]

Originally Posted by M5FirstEdition

The car has only 11,000 miles on it. I took it to 2 different dealerships last week and they didn't believe it's a common issue for this platform. They simply brushed it off and said this perhaps this happens in hot climates like Arizona and California.

Anyhow, After spending days reading about the issue I decided to change the cap and see if the issue still persists.
I can also confirm that the caps between the old and new design are slightly different when it comes the quality of material. See photos.

The cap on the right is the new one.
Execuse my ignorance in using this format. I am new to the forum.

Coolant expansion tank failure is literally the most common problem with this car. Just search this forum. You may also want to share the following with the dealer:

https://static.nhtsa.gov/odi/tsbs/20...25107-9999.pdf

[Tiz113]

How they can say its not a common problem is beyond me. There are a ton of members here that have coolant tank leaks along with the many threads on it. Aftermarket companies even make a shield that sits under the tank to prevent the coolant from leaking on the spark plugs and ignition coils for if or when the tank leaks.

Post i made about mine being replaced under warranty:
https://f90.bimmerpost.com/forums/sh...&postcount=235

Original Thread:
https://f90.bimmerpost.com/forums/sh....php?t=1945250

If the cap doesnt fix the issue its most likely a pinhole leak in the tank somewhere and BMW will replace under warranty. If they do replace it make sure they check the plugs and coils that site directly under the tank

[M5FirstEdition]

Originally Posted by Tiz113

How they can say its not a common problem is beyond me. There are a ton of members here that have coolant tank leaks along with the many threads on it. Aftermarket companies even make a shield that sits under the tank to prevent the coolant from leaking on the spark plugs and ignition coils for if or when the tank leaks.

Post i made about mine being replaced under warranty:
https://f90.bimmerpost.com/forums/sh...&postcount=235

Original Thread:
https://f90.bimmerpost.com/forums/sh....php?t=1945250

If the cap doesnt fix the issue its most likely a pinhole leak in the tank somewhere and BMW will replace under warranty. If they do replace it make sure they check the plugs and coils that site directly under the tank

You think it's a pinhole issue even my coolant level isn't decreasing?

[Tiz113]

Originally Posted by M5FirstEdition

You think it's a pinhole issue even my coolant level isn't decreasing?

When mine happened i never got an error saying i had low coolant, i just noticed the residue around the tank so it is possible there could be. I would just keep an eye on it and if it keeps happening with coolant getting everywhere then its most likely a leak.

[Maverik259]

its just a bad design. the leaks are almost always coming from the cap and tank interface. whether its a bad cap or an issue with the threads of the tank is unknown. either way it allows hot liquid to escape from under the cap and come out. could even be a failure of the 200bar relief valve.

[pbonsalb]

BMW has been using 200kpa or 2 bar or 29 psi caps for over 15 years. 29 psi is a lot of cooling system pressure. I am curious whether the pressure is being exceeded or whether there is some defect.