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E46 M3 (2001-2006) Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006.


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Old Fri, Apr-06-2018, 04:14:04 PM   #1
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Default PSA difficult to find oil leak at motor / trans. Flyweel bolts, clean your crank hub

Over the last 8 months (off and on) I have been trying to find the source of an oil leak at the back of my motor that begins about 3" up to the right side where the motor meets the trans. This is in the vicinity of the CPV.

While searching I saw that a lot of individuals have experienced the same type of leak. Most said CPV (some it was), but I didn't have oil that high, mine was dry. Others said check VCG (again, this solved some peoples issue, not mine). I did this 2 times and resealed the 2nd once twice. VCG was 100% dry and leak free, but I still had the leak.

On the back of the head there's a few freeze plugs and hex head caps, I checked these as best I could to confirm they were dry. It was rare, but a few people had this leak. This was not an issue on mine I believed.

At this point I figured the oil pan was leaking and maybe turbulence under the car was blowing it up slighty...I did the pan, this time with hylomar as a sealant...fired the car up and it still leaked. At this point I am pissed.

My symptoms were the car would only leak when driving, or idling for 30+ minutes on stands, level. I figured it had to be the rear main seal at this point, but I heard that was a non issue on these cars. I got a dye kit as a last resort before I tore it all down just to see. All the kit did was confirm that the oil was coming from inside the bell housing.

This is where it gets interesting. Looking in the peep holes, I could see the UV light revealed oil spatter on the back of the flywheel, but only on what appeared to be about 1/4 of the way around. It was hard to see, but that made me think it wasn't the RMS as the spatter should have been all the way around.

Having exhausted all of my option, I ordered the RMS anyway and dropped the trans. It was the only way to really see what was going on back there either on the head, block, seals etc. When I got everything apart I confirmed that the spatter was only 1/4 of the way around the flywheel, but the oil was coming from the bolt holes, NOT the RMS at the crank.

I looked at everything further and I had a build up of Loctite red on the face of the hub where it meets the flywheel...the UV light showed contamination on the hub at the 3 bolt holes where the spatter was coming from. So when the car would run, it would take a while for oil to work passed the these three bolts, then it would get slung around the bellhousing. Eventually it would be enough to run down the passenger side due to the tilt of the assembly and pool / leak at the bottom. This is why it would have to be after 30 min idle or a drive with more RPM's.

I did the clutch about 1500 miles before all of this and when I did, just used reloctite on bolts, didn't really clean the threads or face of the hub. Now I know. Contamination there could lead to oil moving passed the bolts to the hub causing a leak. This time I cleaned the face of the hub, vacuumed the threads and removed all debris. Idled for an hour yesterday and bone dry.

Tl, DR if you take your flywheel off, clean the face of the crank hub and the crank threads or oil can sneak passed causing a ***** of a leak. I read threads where guys replaced the RMS three times before reporting they stopped the leak. This could have been the issue.



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Old Fri, Apr-06-2018, 04:59:48 PM   #2
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Default Re: PSA difficult to find oil leak at motor / trans. Flyweel bolts, clean your crank

Matt,
This is a very bizarre and interesting finding. I am wondering why loktite on flywheel bolts was not keeping that in.

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Old Fri, Apr-06-2018, 06:01:11 PM   #3
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Default Re: PSA difficult to find oil leak at motor / trans. Flyweel bolts, clean your crank

Not the best penis drawing ever, so 6/10 on that, but great sleuthing to find the leak!
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Old Fri, Apr-06-2018, 06:02:43 PM   #4
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Default Re: PSA difficult to find oil leak at motor / trans. Flyweel bolts, clean your crank

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Originally Posted by TboneM3 View Post
Not the best penis drawing ever, so 6/10 on that, but great sleuthing to find the leak!
LOL

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Old Fri, Apr-06-2018, 07:16:10 PM   #5
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Default Re: PSA difficult to find oil leak at motor / trans. Flyweel bolts, clean your crank

Haha I’ll work on that. And I’m not sure on the loctite. Maybe I was shy with it? I have a feeling that because I didn’t clean the old debris out of the threads or off the hub that it left a path for the oil to travel. I just took the car out, got it real good and hot and got on it a bit. Came back and dry, very happy to put this one behind me. It was a real pain in the ass.


Lots of similar threads - hope it helps someone..it will most likely show recently after a flywheel install.
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Old Fri, Apr-06-2018, 10:09:39 PM   #6
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Default Re: PSA difficult to find oil leak at motor / trans. Flyweel bolts, clean your crank

This might be the leak I've been chasing the last 5 years, but i'm not going to through this trouble to find out it's not. I checked all the usual suspects also. Had BMW change out my RMS when I had my clutch/flywheel replaced. They may not have done it correctly since I continued to have the leak afterwards. I only lose half a liter of oil every oil change so not too bad.

Last edited by aznniche; Fri, Apr-06-2018 at 10:24:41 PM.
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Old Sat, Apr-07-2018, 03:18:08 AM   #7
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Default Re: PSA difficult to find oil leak at motor / trans. Flyweel bolts, clean your crank

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Originally Posted by aznniche View Post
This might be the leak I've been chasing the last 5 years, but i'm not going to through this trouble to find out it's not. I checked all the usual suspects also. Had BMW change out my RMS when I had my clutch/flywheel replaced. They may not have done it correctly since I continued to have the leak afterwards. I only lose half a liter of oil every oil change so not too bad.
Itís not too bad of a job, but all that aside, if you have a similar leak, with the trans out, identifying it should be very easy. Toss some dye in.
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Old Sat, Apr-07-2018, 02:20:26 PM   #8
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Default Re: PSA difficult to find oil leak at motor / trans. Flyweel bolts, clean your crank

So if Iím understanding this correctly the locktite on the face of the crank kept the flywheel from mating 100% perfectly and it allowed oil to seep past the bolts on the crank and splatter around a bit?


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Old Sat, Apr-07-2018, 03:08:06 PM   #9
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Default Re: PSA difficult to find oil leak at motor / trans. Flyweel bolts, clean your crank

Yea that's what I believe happened, along with debris (old Loctite) in the threads of the crank.

The shit was flaking everywhere on the face of the crank as you can see. I had a can of brake cleaner and that plastic pointer and scraped the whole thing off until it was all gone. Then I used a twisted paper towel in the threads, then vacuumed them with a piece of 3/8 line and then twisted them out with an alcohol wipe once more.

When installing, I pressed the FW up to the hub as best I could and used a generous amount of Loctite red on the bolts, this time on the last half of the threads only.

If I could change one thing I did, I would bolt the flywheel on at maybe 5 ftlbs then remove 1 bolt at a time and apply the Loctite. This way, the flywheel with be held completely flush while everything is going together. Not necessary, but next time. Also I suggest not being shy with the Loctite...it also seals the threads from that oil coming through. I know its a catch 22 with it spreading between the faces, but if you do what's written just above that should bullet proof it.

This has to be the issue that these guys who did their ream main 3 and 4 times had.
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Old Sat, Apr-07-2018, 07:49:26 PM   #10
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Default Re: PSA difficult to find oil leak at motor / trans. Flyweel bolts, clean your crank

Never did this job on a e46 so i wouldent know but i never thought the other side of the threaded crank is exposed to oil like that. this is good to know.
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Discussing PSA difficult to find oil leak at motor / trans. Flyweel bolts, clean your crank hub in the E46 M3 (2001-2006) Forum - Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006. at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)