[Dan A]

A couple weeks ago, was driving all over town, got home and was about to go out again and saw a huge puddle under my car as I was pulling out. I got out and it was oil/coolant. I pulled back in the garage and popped the hood and this oil/coolant sludge was coming through the expansion tank and running down. Car had been running fine all day and didn't have any warning signs something was wrong.

First thought was head gasket but then I was reading it could be the oil filter housing gasket. Pulled that and sure enough it failed, allowing coolant and oil mix.

It's since been parked. I probably can't get to fixing it for another few days at least. I'm assuming there is also coolant in my oil sump and hopefully hasn't caused any bigger damage. I have not yet drained out fluids.

Plan is to replace the gasket, button it back up, change the oil, flush the cooling system, and probably do another oil change after I get it warmed up.

Couple questions...what's the best way to flush the cooling system to get the oil out of there? Water pump is pretty new, so hope that isn't damaged. My other question is whether all the cooling system hoses are going to need to be replaced? Will the oil wreck those?

What a mess.

Oh yeah, it's an 08 335xi.

[e91Owner]

You'll get a lot opinions on this as unfortunately it is a common problem. Do a search and you'll find many methods.

Personally I would flush the system several times with a radiator cleaner until you no longer see a slick in expansion tank followed by water, draining each time. With the electric pump, you can do this with the bleed procedure. If you can cycle the cleaner with the engine slightly warm, it will help clear the oil.

You can also just cycle fresh radiator cleaner through the system and discard the return fluid by disconnecting the return line, but you need a few special tools for this which you may not have like a Lisle funnel and an expansion tank line cap.

After draining the oil if there is any residual coolant in the system, it's unlikely that it will be enough to cause problems, but you can always do a second oil change after driving for a little bit if you are concerned.

As far as the hoses, oil is not good for them, but the degree to which they are affected depends on how long it has been cycling through the system. If the hoses are old, you may take the opportunity to change them.

[lobotomy]

I agree with E91 owner, it is exactly what I would do. Only thing I want to add is to use 100% DISTILLED water for the final flushing process. On final fill, use distilled water if cutting anti freeze mixture.

[Dan A]

Thanks for pointing me in the right direction. I was able to find a couple threads on using the return line for flushing the cooling system. Got the replacement gasket yesterday so will try to find some time to work on it soon, I hope. I've had the gasket fail before but not internally - just to where oil leaks on the outside of the housing. I could not find history on where I got the gasket last time, I suspect I used the URO brand one that the local parts store carries. Should have known better. Not that the OEM one doesn't fail either, but this failed too soon and in a bad way.

Yes, I always use distilled water if I'm doing the mix myself, which I'll need to do for the full flush.

Thanks again.