Hey guys, I'm working through diagnosing a coolant leak in my recently acquired 2006 r53. I checked the thermostat, found that it was leaking, replaced the thermostat + gasket today. It looks like that leak has been stopped, but I added distilled water to about the halfway mark in the coolant reservoir to check. About 30 seconds later I had a couple of prett substantial drips under car. I crawled under and took this video -
It appears that the water/coolant is leaking out of the transmission bell housing. You can see in the video that both of the leaks are right along the seam between the engine and transmission. What's more, the one leak is on the bottom and not on the lowest point where any water dripping from the side would leak from.

What would cause coolant to get into the bell housing? My next plan is to pull the head to inspect the head gasket. That's the only way I can think that it could possibly get in there. The thing is though that there hasn't been a mixing of coolant and oil, so it's not your a-typical type of head gasket failure if that's the case. Maybe the outside of the gasket has failed so its leaking externally? Maybe there's a crack in the head?

Any thoughts are appreciated.

 

That's really really strange.
My first thought is that it's leaking up near the thermostat housing and running down into the bell housing.
Maybe drain the system and pressure test it to see if you can hear where the air is escaping from?
I don't think pulling the head is going to help, it sits above the bell housing, not next to it. So if the head was cracked or the head gasket was bad and leaking externally it would be outside the bell housing.

 

Could it possibly be a freeze plug? Would be extremely strange especially since the car has been in San Francisco it's whole life.

I just did a test. I removed the radiator and added a bit of distilled water. Water started coming out of the front water pump where the hose attached (the hose is off), but no water came out of the bottom of the engine/transmission. So that would suggest the leak is above the water pump. That should rule out a freeze plug.

 

Lot of coolant lines and thermostat above the housing…

maybe remove the air box and the battery to get a better look. My guess is a hose leak

also a bleed screw right above there

 

Update on this. I've replaced both the thermostat, gasket, and the coolant temp sensor which were leaking. I'm still getting a pretty prominent leak which was shown in the video from the original post. The only thing I can think it's that it's the head gasket given the location. Can anyone think of anything else I should check before I start tearing into the head?

Video of the leak itself -

 

Lower radiator hose where it attaches to the engine block, it’s right next to the bell housing.