[-PM-]

Hey guys. First post, as I am new-ish to the N platforms (plenty of M and old S experience though).

So here's a crazy situation I am currently facing with this N55:
I got my hands on a 2014 M235i with a bad head. The car ran and drove and even built boost, but cylinder 3 was toast.
Got a replacement head, rebuilt, machined, flow tested, etc. Replaced the head, got everything buttoned up. Started up the car for roughly 45-60 seconds, with oil only (no coolant) to make sure it's timed correctly and running right. All is well at this point. Shut the car down.
Go to pour the coolant into the expansion tank; a gallon goes in right away (that's about what I drained before taking the original head off); the expansion tank is still empty. I proceed to pour in another gallon. It eats it up. Expansion tank is once again empty. This is all with engine OFF. At this point I know something is wrong.

Turns out all that coolant went directly into the oil pan! I removed the oil drain bolt and all that coolant came rushing out, followed by all the engine oil.
To test, I left the drain bolt off and proceeded to pour a half a gallon of clean distilled water into the expansion tank again. Sure enough, 5-10 seconds later it all comes gushing out of the oil drain pain.

How is this possible? Where could it possibly be draining directly into the oil pan?
I checked all the oil and coolant lines that were taken off, and everything seems to be reconnected correctly. There really is only one way to get every line on to fit properly. There are no external oil or coolant leaks either.
It's like the fluid goes down the expansion tank hose, and magically finds a route into the oil pan.
I spent 3 hours soaked in coolant under the car, trying to find an obvious culprit. Nada.
Any ideas or suggestions are more than welcome!


Thanks!

[435gc]

Not sure how this is possible. Not to be a jerk, but are you sure you are pouring into the coolant tank?

[-PM-]

No worries. I did say ANY ideas or suggestions are welcome haha!
And yes, the coolant expansion tank on the passenger side.
I still have no clue how this can happen.

Are there any spots where coolant and oil passages are very close to each other?

Any hoses or lines that can easily be mixed up at re-assembly?
I've tripe and quadrupled checked every line and everything seems to be correct.
Turbo oil feed on top. Oil return on bottom.
Turbo coolant feed and return on side.

How can this be happening? It's mind-boggling.

[BillyT]

Wild stab. Crack in the cooling jacket in the block?

[-PM-]

Originally Posted by BillyT

Wild stab. Crack in the cooling jacket in the block?

Was a thought I had as well. But how realistic would it be for a block to magically crack while non-running with no head on it, between last shut down and first start up with the new head?
When car was shut down last, it definitely did not have a cracked block nor any coolant in the oil pan at all.

[BillyT]

Scratch that then. There must be some connection between the cooling jacket and the oil system. Unless something got under the head gasket or it's in improperly I'm out of ideas. Let us know when you find the problem.

[435gc]

I believe coolant circulates though the oil filter housing. Maybe look there?

Even if an issue there Im not sure you would get the coolant into the oil as quick as you are describing.