I awoke to a coolant leak nightmare

[Horokiwi_Hori]

Hi men and women of the forum.
I literally woke up to a nightmare. After a short drive yesterday, my 2013 E92 M3 (ex UK) warned of low coolant when I got home.
This morning when I checked there is a puddle under the car in line with the rear set of O2 sensors behind the cats.
I removed covers and took the attached photo.
I have coolant dripping once ever 8 seconds from what RealOEM.Com labels "Water outlet hose, splash wall, right" on a slide called "> Heater and Air Conditioning > Collective function group" - M3 diverse small parts.
The pic I took shows a drip forming on the part that looks like a breather. The photo is taken looking up the right-hand side of the DCT, with the pan just obscured and the rear O2 sensor wiring visible.
What I need help with is where to from here to resolve this leak?
The RealOEM diagrams don't clearly show what the "Water Outlet Hose" drains.
I assume it is the heater core area in the cabin? The leak roughly lines up with the door hinges - I imagine its in the vicinity of the heater core.
Do I have to embrace a heater core replacement job?
I'm stuck friends. Any help will be greatly appreciated.
I guess I may as well drain the system while I try and get a real understanding of the problem.
Thanks for all the history, I have searched and founds plenty of distractions. no Snap moment.
George in NZ

[Horokiwi_Hori]

Here is the RealOEM diagram. Sadly, I can't relate this to another diagram to better understand where to find the coolant leak.

[DrFerry]

Originally Posted by Horokiwi_Hori

Hi men and women of the forum.
I literally woke up to a nightmare. After a short drive yesterday, my 2013 E92 M3 (ex UK) warned of low coolant when I got home.
This morning when I checked there is a puddle under the car in line with the O2 sensors ahead of the cats.
I removed covers and took the attached photo.
I have coolant dripping once ever 8 seconds from what RealOEM.Com labels "Water outlet hose, splash wall, right" on a slide called "> Heater and Air Conditioning > Collective function group" - M3 diverse small parts.
The pic I took shows a drip forming on the part that looks like a breather. The photo is taken looking up the right-hand side of the DCT, with the pan just obscured and the O2 sensor wiring visible.
What I need help with is where to from here to resolve this leak?
The RealOEM diagrams don't clearly show what the "Water Outlet Hose" drains.
I assume it is the heater core area in the cabin? The leak roughly lines up with the door hinges - I imagine its in the vicinity of the heater core.
Do I have to embrace a heater core replacement job?
I'm stuck friends. Any help will be greatly appreciated.
I guess I may as well drain the system while I try and get a real understanding of the problem.
Thanks for all the history, I have searched and founds plenty of distractions. no Snap moment.
George in NZ

It could be #13 or #11 in the photo below.
.
https://www.m3post.com/forums/newrep...ply&p=30879118
.

[Horokiwi_Hori]

Thanks for the quick suggestion. I felt like I needed to clarify the leak location better and its actually dripping from the "breather tube" onto the rear O2 sensor wiring harness.
My thinking is if the leak was occurring in front of the cats, I'd see the drip further forward? Before I removed the covers, I'd describe it as the DCT is leaking radiator coolant.

[DrFerry]

Originally Posted by Horokiwi_Hori

Thanks for the quick suggestion. I felt like I needed to clarify the leak location better and its actually dripping from the "breather tube" onto the rear O2 sensor wiring harness.
My thinking is if the leak was occurring in front of the cats, I'd see the drip further forward? Before I removed the covers, I'd describe it as the DCT is leaking radiator coolant.

You need to consider the coolant "drip path" as it works its way down to the ground. Since the heater core is metal, my money is on the smaller feeder hose at the back of the engine. Number 11 I think which may have a small pin hole or split in it or perhaps just a crack at one of the clamp crimps. Hello in NZ from USA South Carolina.

Edit:
Could also be hoses 21 or 22.
.
https://www.realoem.com/bmw/enUS/sho...98#11537838215
.

[Brandoch]

The HVAC unit has a drain hole that leads right over top of the transmission. This drain hole allows coolant to escape if the heater core leaks.

[DrFerry]

Originally Posted by Brandoch

The HVAC unit has a drain hole that leads right over top of the transmission. This drain hole allows coolant to escape if the heater core leaks.

Uh oh.. Big job to replace the core....
.

[Brandoch]

Originally Posted by DrFerry

Uh oh.. Big job to replace the core....
.
https://www.youtube.com/watch?v=ah3xUzMF_b8

Ask me how I know lol

[Horokiwi_Hori]

Thank you Brandoch and DrFerry. The "ask me how I know" is exactly what I needed to hear. My interpretation of that is that you had this issue and you advised the fix.
I felt sure this leak was in the vicinity of the heater core.
Talk about stab it in and twist it. I feel like they broke it off as well!
I have a choice of 5 heater cores, and no way of knowing which I should order until the car is apart. I guess I won't be at the Masterton Motorplex drag strip this weekend.
That bites.
But on a positive note, the forum works really well. Thanks again.

[DrFerry]

Originally Posted by Horokiwi_Hori

Thank you Brandoch and DrFerry. The "ask me how I know" is exactly what I needed to hear. My interpretation of that is that you had this issue and you advised the fix.
I felt sure this leak was in the vicinity of the heater core.
Talk about stab it in and twist it. I feel like they broke it off as well!
I have a choice of 5 heater cores, and no way of knowing which I should order until the car is apart. I guess I won't be at the Masterton Motorplex drag strip this weekend.
That bites.
But on a positive note, the forum works really well. Thanks again.

Good luck with the repair job. When you say above, “I feel like they broke it off”. Who is “they”? Did someone damage your heater core? Let us know how the repair work progress goes? There’s not a lot on the forum about the topic. Though plenty on YouTube.

[Horokiwi_Hori]

OBSERVATION:
Before I knew the heater core / AC Evaporator was damaged, I was searching the forum to try and understand a strange behavior that made no sense to me. I was searching for "Cooling system pressurizing without starting the engine".
SYMPTOM:
I checked the coolant level after the car had been sitting a week or so, and the cooling system was pressurized, and overflowed.
RANT:
Its summer here and I had the heat off, I expect a tap/faucet is actually closed in the cooling system to prevent heat in the cabin. With the car in the garage I guess it got to 30 degrees C. during the day and down to 15C overnight.
I think the cooling system was able to suck air but not expel it? Hopefully this footnote helps someone trying to understand what could cause said dilemma?

[Horokiwi_Hori]

Here's the twist...
The evaporator is different for LHD and RHD cars.
Naturally I have had the LHD item delivered and my car is RHD. RMA my LHD and order my part from a non-USA supplier.
Half my fault. Hopefully this post might help someone order the correct part in future.