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Old 06-24-2019, 07:04 AM   #1
JGood
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m6x rear main seal issues

My e30 suddenly started leaving small puddles of oil under it, and it appears to be coming from the rear main seal. I'd say maybe a baseball size puddle after I drive it each time. There's a decent amount of oil covering the bottom of the car as well, looks like it's leaking when running too. This is an m62 block with m60 heads, that has been leak free since I put it together ~5 years ago, maybe 30k miles or so. I resealed the entire engine at that time, including the rear main and rear cover gasket.

I'm a little worried that it suddenly began puking a significant amount of oil, out of nowhere, with such little mileage. Has anyone else had rear main seal issues?

I see BMW sells a "rear main seal kit" of sorts, including a new rear cover with a seal already pressed in, and a new gasket included. This is significantly more expensive than buying a seal and gasket alone, but I'm wondering if it's a better idea to ensure a perfect seal. This is not a job I want to do more than once.

Ideas, experience, thoughts?
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Old 06-24-2019, 09:43 AM   #2
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They just leak after awhile. N63s are really bad about it. When you replace it use a fine scotchbrite pad to smooth the sealing surface of the crank. If you replace the whole plate make sure you put a couple of dabs of RTV on the corners when it meets the oil pan.

If you replace just the seal put some anaerobic sealant on the outside of the seal and a very light coat of oil on the crankshaft sealing surface.
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Old 06-24-2019, 09:52 AM   #3
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My dad used a product called Blue Devil on the RMS leak in his E24. The first can reduced the volume of the leak, while the second can stopped it completely.

Are there alignment dowels between the block and the rear cover? Is it possible that the seal bore in the cover was out of concentricity relative to the seal journal on the crank, resulting in short seal life?
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Old 06-24-2019, 12:37 PM   #4
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They just leak after awhile. N63s are really bad about it. When you replace it use a fine scotchbrite pad to smooth the sealing surface of the crank. If you replace the whole plate make sure you put a couple of dabs of RTV on the corners when it meets the oil pan.

If you replace just the seal put some anaerobic sealant on the outside of the seal and a very light coat of oil on the crankshaft sealing surface.

Yeah I took those steps when I put the engine together. I just find it hard to believe that I have a rather sudden, serious leak. I know BMW v8's are notoriously 'leaky', and almost every gasket on this engine does have some amount of seeping oil, but this went from dry one day, to leaving puddles the next day. To me, that sounds like something actually failed.

I did notice that the rear cover bolts use a washer with a rubber gasket built in. I do not recall purchasing, or even seeing these upon disassembly, so I may have used plain washers. That said, the gasket includes a 360 degree sealing surface around the bolt holes, so they should just be redundant sealing.

I think I'm going to run some UV dye through the engine immediately prior to removal, to hopefully pinpoint the leak once it's apart.
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Old 06-24-2019, 12:57 PM   #5
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Have you been consistently running the same motor oil?

Buddies RMS was leaking like crazy when he was using synthetic Amsoil. Switched to Rotella t non synthetic and not a drop after.
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Old 06-24-2019, 01:26 PM   #6
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Have you been consistently running the same motor oil?

Buddies RMS was leaking like crazy when he was using synthetic Amsoil. Switched to Rotella t non synthetic and not a drop after.



Yeah, Mobil 1 10w30 Full Syn. It is due for an oil change, maybe I'll switch it up and see what happens, before I tear it all apart.
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Old 06-24-2019, 02:56 PM   #7
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Yeah, Mobil 1 10w30 Full Syn. It is due for an oil change, maybe I'll switch it up and see what happens, before I tear it all apart.
Give the Blue Devil a shot while you're at it.
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Old 06-24-2019, 04:12 PM   #8
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Originally Posted by The Dark Side of Will View Post
My dad used a product called Blue Devil on the RMS leak in his E24. The first can reduced the volume of the leak, while the second can stopped it completely.

Are there alignment dowels between the block and the rear cover? Is it possible that the seal bore in the cover was out of concentricity relative to the seal journal on the crank, resulting in short seal life?

I can attest to this stuff. I had a front crank seal tear and start leaking HEAVILY. I knew it was going to be at least a month and half before I could get the time to do the job and with the car being a daily I needed it to survive. I tossed a bottle of the blue devil rear main sealer in and the leak almost stopped. I was seriously impressed. It wasn't on an m60 or anything but a crank seal nonetheless.
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Old 06-25-2019, 08:10 AM   #9
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Yeah I took those steps when I put the engine together. I just find it hard to believe that I have a rather sudden, serious leak. I know BMW v8's are notoriously 'leaky', and almost every gasket on this engine does have some amount of seeping oil, but this went from dry one day, to leaving puddles the next day. To me, that sounds like something actually failed.

I did notice that the rear cover bolts use a washer with a rubber gasket built in. I do not recall purchasing, or even seeing these upon disassembly, so I may have used plain washers. That said, the gasket includes a 360 degree sealing surface around the bolt holes, so they should just be redundant sealing.

I think I'm going to run some UV dye through the engine immediately prior to removal, to hopefully pinpoint the leak once it's apart.

Excessive crankcase pressure or vacuum can cause the seal to “fail” as well. For example I’ve seen CCV valves on M54s and N52s fail causing an absurd amount of crankcase vacuum and literally pull the seal “flaps” if you will in and let oil leak past. I know that’s probably not what’s going on with your car but if it were me trying to diagnose it I would be trying anything and everything to avoid pulling the transmission.
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Old 06-27-2019, 04:49 AM   #10
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I changed the oil, it had been longer than I thought. 4k miles and 10 months. Previous oil was Mobil 1 5w30, switched to Mobil 1 10w30. No change, still leaking.

I'll get a vacuum gauge on it and check crankcase pressure as well.

I don't think I want to use any leak-stoppers. If this was an old engine, sure. But all of these seals and gaskets are fairly new, none of them are going to be hard and dry, especially the rear main. That's how they work... swelling and softening the dry, hard seals. I have no idea what it would do long-term to all of the spots where I used gasket maker (timing cover junctions, etc). Last thing I want to do is create more issues.
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Old 06-27-2019, 08:28 AM   #11
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I changed the oil, it had been longer than I thought. 4k miles and 10 months. Previous oil was Mobil 1 5w30, switched to Mobil 1 10w30. No change, still leaking.
That's not much of a change?

M60/M62 is "rated" to run 15w40 conventional (07510017868) or 5w30 synthetic (07510017866).

Realistically the engine was designed for 15w40 conventional.

No one is saying that it should leak with 5w30 synthetic, but when it comes to leaks, 15w40 dino should make a big impact.

Get a bottle of Rotella T4 15w40. Enjoy the added ZDDP complimentary of looser diesel regulations.
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Old 06-27-2019, 09:47 AM   #12
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That's not much of a change?

M60/M62 is "rated" to run 15w40 conventional (07510017868) or 5w30 synthetic (07510017866).

Realistically the engine was designed for 15w40 conventional.

No one is saying that it should leak with 5w30 synthetic, but when it comes to leaks, 15w40 dino should make a big impact.

Get a bottle of Rotella T4 15w40. Enjoy the added ZDDP complimentary of looser diesel regulations.

I didn't change it thinking the rated weight would make a difference, I changed it thinking the old oil may have sheared to the point where it lost significant viscosity. I knew it was unlikely, but I was due anyway. I've been running 10w30 Mobil 1 since I put the engine together 5 years/30k miles ago, and it's been leak free. Last oil change I used 5w30, I don't remember why, maybe they were out of 10w30 Mobil.

With 10w30, I see very high oil pressure. 20psi at 600RPM idle, 60psi by 1k RPM, 70psi up to about 5k, 80+psi over that. That's all at the fully warmed up operating temp. That's why I never used anything thicker.

There is no way oil is literally running out of the rear main seal suddenly due to using 30 weight instead of 40 weight oil, when I've been using it all along. If it was a drip every 1000 miles, okay. But I get a large puddle after running the engine for 15 minutes. There has to be a failure of the seal/sealing surface.
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Old 06-27-2019, 01:51 PM   #13
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I didn't change it thinking the rated weight would make a difference, I changed it thinking the old oil may have sheared to the point where it lost significant viscosity. I knew it was unlikely, but I was due anyway. I've been running 10w30 Mobil 1 since I put the engine together 5 years/30k miles ago, and it's been leak free. Last oil change I used 5w30, I don't remember why, maybe they were out of 10w30 Mobil.

With 10w30, I see very high oil pressure. 20psi at 600RPM idle, 60psi by 1k RPM, 70psi up to about 5k, 80+psi over that. That's all at the fully warmed up operating temp. That's why I never used anything thicker.

There is no way oil is literally running out of the rear main seal suddenly due to using 30 weight instead of 40 weight oil, when I've been using it all along. If it was a drip every 1000 miles, okay. But I get a large puddle after running the engine for 15 minutes. There has to be a failure of the seal/sealing surface.
The flow characteristics and additive packs in dino vs synthetic are completely different. Synthetic can flow through small crevices much better.

Certainly the synthetic didn't cause the leak, and I agree its a seal failure. Never the less, synthetics have gotten substantially better over the last 20 years and even more so since they designed the M60. They just flow too good sometimes, particularly when a seal is less than perfect.

I wouldn't have suggested it if I hadn't seen it with my own two eyes. Like I said, buddies RMS was leaking to the point of making a puddle, after switching rarely does he even see a drop.

At the rate your leaking, you'll need to buy more oil soon anyways. Give it a try.
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Old 06-27-2019, 02:05 PM   #14
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If you made it 5 years on an M60 without leaks, you should be buying a lottery ticket
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Old 06-30-2019, 07:05 PM   #15
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I said screw it and yanked the engine. I ordered the new (expensive) rear main seal kit from BMW, with the seal already pressed into a new housing.

When I pulled the old seal housing off the block, I noticed the seal was seated crooked. I pushed on it a little bit, and it damn near fell out.

Pretty sure you shouldn't be able to do this:

https://www.youtube.com/watch?v=-_5bqJHJm7c

The new seal looks quite a bit different. Bare metal outer case, instead of fully coated rubber, and also has an inner and outer sealing lip, instead of just 1, and measured a slightly smaller ID. The old seal was also significantly harder than I expected for 5 years/30k miles.










The new housing casting looks a bit cheaper/shittier to me, but I'm not an engineer, it's probably just fine. The sealing surfaces look fine, guess that's all that matters.

Got the new parts on, and the trans back on the engine. Tomorrow evening I'll put the engine back in the car, hopefully finish everything up Tuesday evening.
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