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Discussion Starter #1
Hi -

I have what appears to be an atomized mist of engine oil that seeps out from underneath the oil fill cap, and I postulate that the aerodynamics of what happens underneath the closed hood at speed is what carries the mist out towards the passenger side.

A tell-tale sign of this is residue of an oil mist on the automatic transmission fluid reservoir, among other parts int he way of the mist as it escapes from underneath the hood.

I have a fantastic shop that I take my M5 to for most work but I wanted to do this myself. The last time I was there, I asked them about the oil filler cap. They said that the rubber gasket feels a little firm. While this may be true, I have no baseline for what elasticity this gasket should have. I trust their judgement though. However, this is a new cap.

I'm about to get deep in to the top end to replace the idle air control valve in bank 1, so figured I'd also address this problem and clean things up while I'm in there.

In a search of the forums, I didn't get any idea that this is a common thing, but I have an open mind and would be ok with someone suggesting that the oil is coming from somewhere else. There are some pictures attached, to describe what I mean.

Thanks!
-dant
 

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Common thing and thats not the auto transmission reservoir, its the power steering reservoir which uses CHF fluid. Your SMG reservoir is on the side of the tranny.
 

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Discussion Starter #3
Common thing and thats not the auto transmission reservoir, its the power steering reservoir which uses CHF fluid. Your SMG reservoir is on the side of the tranny.
Wish I could delete the original quite and make it look like I actually know what I'm talking about. I'll blame the head cold. Sorry about that.

What's a common thing, the filler cap not having a great seal? What suggestions might be out there to make this a not-so-common thing?
 

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BMW power steering reservoirs are notorious for leaks. There are some tricks to help, which I have never paid attention to. There's a weep hole where it comes out of, once in a great while sure the gasket on the bottle or cap could be bad. I have seen people tie socks around the bottle to catch it.
 

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Let's check basics first: is the PS fluid level too high?

If fluid is at the second mark when cold then it WILL spill (found out at the track).
 

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That engine bay is embarrassing. Sorry I couldn't hold it in.
 

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I know its probably obvious but clean everything up and check it out after a hard drive. No other way around that.

(To me it just looks like years of neglect)
 

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Discussion Starter #10
Decided to investigate this a little more while I had the plenums off to replace the idle control valve.

Looks like the o-ring between the oil filler neck and the valve cover is compromised. Here's some pictures before I hit it with some degreaser and a spritz of water. I haven't visually or physically confirmed, but now that I've got a better idea of the spray pattern, I'm pretty certain that's it. Removing the ignition coil cover for inspection helped. I'll wait until everything is all dried up and wiped down again before attempting to remove the neck and confirm, don't want to get any of those oil boogers in the case.
 

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Discussion Starter #11
A year later, and my, what has changed.... and again, what hasn't.

At the time I posted this, I was also replacing an idle air control valve. Since I had the battery disconnected, I decided to give everything a deep steam degreaser clean.

Since then, I've also done every part of the driveline behind the transmission (flex disc, pinion seal, output seals, all new rubber, washers, learned about torque-to-yield bolts.............). I love this car.

The leak that I had original described persists, despite having replaced the oil fill cap, neck, and o-ring. It never got worse, it was just persistent. It's not gushing out oil but it's definitely still venting and atomizing some oil at pressure. There's even an oil stain right above the oil fill cap, against the mat that attaches to the underside of the bonnet.

We've learned about the power steering fluid reservoir leaking. That doesn't seem to be the case here. But are the oil fill caps also notorious for leaking? The cap I replaced the original with is an OEM replacement. The washer underneath it is still rubbery, but it feels quite stiff. That being said, I'm wondering if there's just a re-engineered version, or an aftermarket one, that is designed to correct this very problem?

(after a good cleaning, awaiting oil filler neck, o-ring, replacement OEM fill cap)

930338


(scrubbing with degreaser and toothbrush continues; no leaks found in or around power steering reservoir or cap)
930339


(ready for a prom date)
930340
 

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Discussion Starter #12
Did some digging today, reading up to get a better understanding of how much oil is enough, or in worse cases too much, and the effect this has on the pressure of the oil system. In such case that there's too much oil (more than the dash description of the "max" arrow (to read > 1L) looks like it can cause what I'm describing. It was interesting to read up on how the volume of oil is measured, and how much to add at which interval according to the OB.

I'll chalk this up to there being maybe 500ml too much oil in the system. That's what I always tried to keep it at, since that's what my shop always filled it to. I'm reading that this may be wrong.

Hope that helps someone.
 

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Discussion Starter #13
So, that was a lie. The oil level was fine.

I did, however, swap out the cap based on some stuff I was reading.

I went with 11121405452, which has a fitment for up until the E46 M3. It fit just fine, and there's no more leaking.
 

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Mine also has some crud around the oil cap. Bought a new cap last week and there's an obvious difference in how tight the new cap seals. Consider the cap another wear item on these cars...
 

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So, that was a lie. The oil level was fine.

I did, however, swap out the cap based on some stuff I was reading.

I went with 11121405452, which has a fitment for up until the E46 M3. It fit just fine, and there's no more leaking.
Hey dan do you mind giving me the link on where to find this cap? Mine is leaking too and I just want to make sure I buy the right one. Thanks man!
 

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Discussion Starter #17
I think you should be fine or during this part number anywhere, except ECS of course :)

AutohausAZ is local and has a will-call so that's where I happened to order mine.
 
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