[Samfoh]

Originally Posted by N54Society

Definitely great points to consider. I'm just talking from practical, hands-on observations on two cars now. The observation I have is that if I mix too much distilled water, I get the boiling on the head. Two N54 cars. I ran the water pump air purge cycle twice with the cap off and then once with it on because I read some where that it was recommended that way as well, so I tried it. I opened the screw, let the air out and closed it back. Ran the car, it started boiling after a short drive. I removed some coolant from the system from the radiator screw, added more G48, ran the cycle once more, and things have been great even after multiple spirited runs. I must be putting too much distilled water is my conclusion. I could pretty much reproduce it at will now that I've seen it with this car as well.

Bumping this to check and see if the problem ever came back? I am have the exact same issue on my 2009 335i. The videos you posted are exactly like mine. From this last post, it seems you didn’t make any repairs, but just adjusted antifreeze ratio and re-bled?

[_N54]

That looks like my ethanol boiling on the cylinder head when I was depressurizing the system to remove the fuel lines.

[Samfoh]

Yeah. It’s very strange. It seems the OP and one other member has had the same issue. It also seems the OP ended up diagnosing the problem as leaking freeze plug(s) using coolant dye, but then only changed the antifreeze mixture without changing or repairing plugs. I just wanted to confirm if that was really a long term solution… it seems so strange that it would make a difference if the problem were really leaking freeze plugs.