Coolant leak from nut on side of cylinder head

[Bennet]

Hi everyone,

I seem to have coolant leaking from a bolt on the left hand side of the cylinder head. I assume this is a drainage bolt for coolant. I'm hoping this is a simple case of taking the bolt out, replacing a rubber seal and screwing it back up - however, I can't find this bolt anywhere on the exploded diagrams on realoem.com.

My questions are:
Has anyone seen a leak from this location before?
Can anyone find this on a diagram or tell me the part number for the seal ring? (I haven't taken the bolt off yet, but I assume there is a seal ring!)

Car is an E85 2.0.

I could just try tightening it, but I assume this is an aluminium head and I don't want to knacker the thread.

Here's a video showing a closeup of the leak https://www.youtube.com/watch?v=lQOhaRyPZ3k
Drip at 13 seconds.
Closeup at around 25 seconds.







https://www.realoem.com/bmw/enUS/showparts?id=BZ12-EUR-07-2007-E85-BMW-Z4_20i&diagId=11_3177

 

[smorris_12]

Looks like someone's lost the drain plug and wound an ordinary bolt in. There won't be a seal as such, that sort of fitting ought to be shaped to bottom out in a matching face to provide the seal. From the diagram the drain plug also comes with PTFE tape wrapped round it to seal the threads too.

Or, if the bolt head that's in there is hitting the top face of the boss then a copper washer under it would make a good seal.

 

[Bennet]

Looks like someone's lost the drain plug and wound an ordinary bolt in.

Maybe! (All though if so, lots of other people have done the same thing! Every picture of the cylinder head I can find online has the same large bolt.)

I could unwind it and put it back in with some tape though. Will ordinary PTFE tape be suitable for something that gets as hot as a cylinder head..?

Thanks for the response.

 

[smorris_12]

Ah. I was going by the parts diagram: they're usually hyper accurate on their detail (hence the comment about tape) - If it shows an Allen headed bolt, that's what I'd expect!

Looking at the video again, if that is the correct bolt then I'm not sure where I'd expect the seal to be. Sealing generally doesn't occur on threads unless one of them is a taper fitting (in general plumbing, not something I'd expect on a car) and the mating face won't be at the end of the bolt or the head wouldn't be hard against the block. That just leaves a flange just under the head mating to the block. And then a copper washer is usual, which I can't see there.

I'd whip out off cold and get a copper washer in there as I have a pile to hand. Otherwise a fresh bolt may be worth obtaining. PTFE is rated to 260C so should be ok but it's an utter fag to keep in place if trying to put a fitting back blind. Especially if you're trying to keep the coolant from escaping while doing it!