[RayLivingston]

My car is a '07 335i with ZF6HP19 transmission. About a month ago, it started "marking its territory" every time it was parked for several hours. It leaves about a 4-6" diameter puddle of oil directly under the post-cat O2 sensor connectors fastened to the bottom of the bellhousing. I can think of several possible sources for this leak:

1) Valve cover gasket
2) Engine oil pan gasket
3) Engine rear main seal
4) Trans input shaft seal
5) Trans Input housing cover O-ring.

I just replaced the valve cover gasket just a few days ago, as it WAS leaking some - I found small pools of oil in the "valley" between the cams. That is now fixed, but the drip persists. I also recently (about ten days ago) replaced all the Mechatronic seals in the trans, and did a fluid and pan+filter change. I re-filled it with LiquiMoly TopTec 1800 fluid, which, sadly, looks almost exactly like engine oil - translucent light brown in color - rather than the more typical ATF red, or the Pentosin blue!

Obviously, at this point, I am PRAYING for an oil pan leak, rather than a main seal leak or any kind of trans leak, either of which would require removing the trans. Ultimately, this oil must be coming from EITHER the engine or the trans, and I would have thought it would be easy to tell the difference, but this is not the case.

Yesterday, I went to the parts store, and got a small bottle of bright yellow/orange UV dye, and put it in the engine oil, then drove for about an hour. When I got home, my drip pan still had the puddle of oil left from sitting overnight on one side, so I rotated the pan 180 degrees, so the "new" drip would land on the other side. After sitting a few hours, I was praying I would find a new puddle of bright yellow/orange oil there, but, after a few hours, I had a second puddle of identical-looking oil! Both puddles fluoresce with the same orangey-brownish color! I then took samples of fresh, new engine oil, and fresh, new trans oil, and looked at them with the UV light. To my surprise BOTH fluorescing under UV light! Cr@P! So, just now I took a sample of engine oil from the oil filter housing, and trans oil I sucked out with a syringe. The engine oil sample matches the drip perfectly - orangey-brownish in color under UV. The trans oil is distinctly more yellowish. Hard to figure, but it appears the dye I put in the oil did NOTHING to change the color! But I now know I have an engine leak, NOT a trans leak, which is really good news.

So, before I tear into the oil pan gasket, is there ANY other potential leak source that could cause it to drip where it is dripping? I can see nothing from above, and there is so much cr@p in the way, I can't really tell what path it is taking. The oil appears to be coming more down the left side of the pan, but I cannot see how far up it starts. But the fact that it is coming DOWN the side of the pan would seem to me to rule out a main seal leak, or a trans leak, as I would expect both of those to leak straight down from the crank, and come out near the center-bottom of the bell housing.

Any thoughts? Other leak sources to check out before dropping the pan? Any other plausible theories?

[RayLivingston]

After poking around underneath the car, it now appears to me the leak is actually on the RH side of the engine, above the pan. Something on the turbos??

Need to find some photos or other documentation on exactly what is over there...

[GrimaldoA]

Originally Posted by RayLivingston

My car is a '07 335i with ZF6HP19 transmission. About a month ago, it started "marking its territory" every time it was parked for several hours. It leaves about a 4-6" diameter puddle of oil directly under the post-cat O2 sensor connectors fastened to the bottom of the bellhousing. I can think of several possible sources for this leak:

1) Valve cover gasket
2) Engine oil pan gasket
3) Engine rear main seal
4) Trans input shaft seal
5) Trans Input housing cover O-ring.

I just replaced the valve cover gasket just a few days ago, as it WAS leaking some - I found small pools of oil in the "valley" between the cams. That is now fixed, but the drip persists. I also recently (about ten days ago) replaced all the Mechatronic seals in the trans, and did a fluid and pan+filter change. I re-filled it with LiquiMoly TopTec 1800 fluid, which, sadly, looks almost exactly like engine oil - translucent light brown in color - rather than the more typical ATF red, or the Pentosin blue!

Obviously, at this point, I am PRAYING for an oil pan leak, rather than a main seal leak or any kind of trans leak, either of which would require removing the trans. Ultimately, this oil must be coming from EITHER the engine or the trans, and I would have thought it would be easy to tell the difference, but this is not the case.

Yesterday, I went to the parts store, and got a small bottle of bright yellow/orange UV dye, and put it in the engine oil, then drove for about an hour. When I got home, my drip pan still had the puddle of oil left from sitting overnight on one side, so I rotated the pan 180 degrees, so the "new" drip would land on the other side. After sitting a few hours, I was praying I would find a new puddle of bright yellow/orange oil there, but, after a few hours, I had a second puddle of identical-looking oil! Both puddles fluoresce with the same orangey-brownish color! I then took samples of fresh, new engine oil, and fresh, new trans oil, and looked at them with the UV light. To my surprise BOTH fluorescing under UV light! Cr@P! So, just now I took a sample of engine oil from the oil filter housing, and trans oil I sucked out with a syringe. The engine oil sample matches the drip perfectly - orangey-brownish in color under UV. The trans oil is distinctly more yellowish. Hard to figure, but it appears the dye I put in the oil did NOTHING to change the color! But I now know I have an engine leak, NOT a trans leak, which is really good news.

So, before I tear into the oil pan gasket, is there ANY other potential leak source that could cause it to drip where it is dripping? I can see nothing from above, and there is so much cr@p in the way, I can't really tell what path it is taking. The oil appears to be coming more down the left side of the pan, but I cannot see how far up it starts. But the fact that it is coming DOWN the side of the pan would seem to me to rule out a main seal leak, or a trans leak, as I would expect both of those to leak straight down from the crank, and come out near the center-bottom of the bell housing.

Any thoughts? Other leak sources to check out before dropping the pan? Any other plausible theories?

How many miles is on your car? Is it the original valve COVER? Oil filter housing gaskets and cracked valve covers are pretty common too. You should check em out if you haven't already.

[RayLivingston]

Car has ~140K miles. Valve cover was replaced about ~6 years/60K miles ago, and has been fine until recently. Seems leak-free now, AFAICT. No oil on manifold heat shields, no smoke. No leaks from OFHG - that was done same time as the valve cover ~6 years ago, and is still clean and dry.

I now suspect one of the turbo oil lines. Trying to figure out how to get a good look up in there to see what's going on. May need to get a borescope.

[mainbearing]

You might also want to check your warranty. In Cali it may be covered 15-years 150K miles.

If the valve cover was not changed, then the plastic could crack and leak.

[RayLivingston]

Valve cover was replaced, and is NOT leaking. I now suspect it's probably leaking from the oil return line for the rear turbo, or (I hope NOT) the turbo itself.

[RayLivingston]

If my leak is the oil outlet pipe from the rear turbo, how difficult is that to replace? What is involved?

[mweisdorfer]

Originally Posted by RayLivingston

If my leak is the oil outlet pipe from the rear turbo, how difficult is that to replace? What is involved?

If you have the subframe out, not horrible. It will probably act like it's stuck until it finally pops out. Don't pry.

[RayLivingston]

Originally Posted by mweisdorfer

If you have the subframe out, not horrible. It will probably act like it's stuck until it finally pops out. Don't pry.

Oh, so it still requires removing the subframe? I was hoping to avoid that. If I have to do it anyway, it would seem foolish to NOT also do the oil pan gasket, no?

[RayLivingston]

Originally Posted by mweisdorfer

If you have the subframe out, not horrible. It will probably act like it's stuck until it finally pops out. Don't pry.

Oh, so it still requires removing the subframe? I was hoping to avoid that. If I have to do it anyway, it would seem foolish to NOT also do the oil pan gasket, no?

[mweisdorfer]

Originally Posted by RayLivingston

Oh, so it still requires removing the subframe? I was hoping to avoid that. If I have to do it anyway, it would seem foolish to NOT also do the oil pan gasket, no?

That would be something you could do "while" you are in there, yes. It depends on how many miles you have on that gasket. Over 75,000 miles = yes

[RayLivingston]

AFAIK, the oil pan gasket is original. I bought the car in '14, with ~70K miles on it.

I've done all the peeking I can to get a handle on the leak. I believe it is the oil pan, and the oil above that is just being blown up there. The exhaust manifolds, and what I can see of the turbos, wastegates, and cats are all clean. No evidence of even past valve cover leaks.

So, off to buy an engine lifting bar, and some good ramps to get the front end up in the air as far as reasonable, so I can take off the sub-frame and pan. When they are off, I'll get as good a look as I can of the turbo area, looking for any other potential problems.

[mainbearing]

If dropping the subframe, maybe engine mounts, thermostat and water pump?

I would recommend removing rear mounting bolts first (the ones going 45 slanted into the chassis), then the middle one and finally the fronts.

There have been two member posts about thread damage for those bolts (https://www.e90post.com/forums/showthread.php?t=1858639). I suspect removing of the bolts while the subframe's weight on them might be the reason (even when supported as mine was). But easily resolved with a Harbor Freight $19.99 tap and die set IIRC M12-1.5 (https://www.harborfreight.com/carbon...-pc-62832.html).

Installation iirc Bentley says to install the fronts first. Therefore reverse the order.

[RayLivingston]

I'll certainly check the motor mounts, and take a look at the pump and thermostat, though they are working fine, and not completely awful to replace in-situ (I've had them out once - can't recall why).

My E46 has a frame stiffener that is similar to the E90 subframe, with similar odd-angled bolts. I ALWAYS put those in by hand far enough to be certain they are not cross-threaded. Never had a problem.

Really not looking forward to this whole job...

[mainbearing]

When I was doing mine, I kept thinking I would gladly pay a shop $1,000. In retrospect I can do it much faster. While not something we want to do, if this is not your first rodeo you should do better than I did.

BMW definitely should have sealed the thing with RTV and avoid all those wasted hours by so many owners. IMO their engineers should be sent to Honda for training first before starting jobs. I wondered if some of them even knew how to change oil before getting the jobs.

The rear of the pan had two "ears" that hung up on a flimsy separator plate with the transmission that caused me to waste hours. Anyway my notes https://www.e90post.com/forums/showp...&postcount=327

[RayLivingston]

Yeah, I really don't understand why they can't make a lifetime oil pan gasket. I've NEVER had to replace one on any other car I've ever owned. Same goes for the OFH gasket. Seems to me a graphited paper gasket would've worked just fine there.