How To Distinguish Engine Oil Leak from Trans Oil Leak

RayLivingston · 08-30-2021, 06:13 PM

My '07 335i has rather suddenly developed a significant oil leak, coming from the very back of the engine. From what I can see, I suspect (hope?) it is most likely the engine oil pan, but it could also be a trans leak inside the bell housing (ZF 6-speed auto trans). The leaking oil is brown-ish, so could be either engine or trans oil. Is there any reliable way to easily tell which it is??

"As we speak", I am doing the Mechatronic seal replacement on the trans, so it is about to get a fill of fresh, clean fluid, which will hopefully make distinguishing between the two sources easier, but I'm wondering if there is any other way to tell.

Welcome to NBA Jam · 08-30-2021, 06:26 PM

Transmission fluid is typically red in color, but the best indicator is how it smells. Transmission fluid is notoriously smelly, like sulfur.

mainbearing · 08-30-2021, 06:34 PM

GM ATF uses red dye, but ZF 6 could be either amber (LG6) like engine oil or green (LG8) as I use in Audis.

I would think the ATF would still be a little thinner than engine oil and would smell different too.

If you are changing the mechatronic sleeve, also change out the tube seals and double-D seal, because you do not want this to happen with the cheap plastics:

https://www.e90post.com/forums/attac...1&d=1502107542

My old seal was still good for the 6HP19 (Audi) when replaced along with the tube seals and the case sleeve:

https://www.e90post.com/forums/showp...86&postcount=4

RayLivingston · 08-30-2021, 07:35 PM

Yes, I am changing the square seal, the four little round ones, and the one on the connector, along with a new oil pan/filter and bolts.

Old tans oil is barely translucent brown-ish, looks and feels about the same as engine oil. Hadn't noticed any particular smell, but I will check that tomorrow.

e91Owner · 08-30-2021, 11:33 PM

If the replacement fluid you are using isn't MERCON SP or other red colored fluid that would make a future leak more obvious, you can always clean the area well and add some UV dye in either the engine oil or ATF to be able to tell better than smell alone.

RayLivingston · 08-31-2021, 12:30 AM

Don't know yet what color the new fluid is - it's LiquiMoly TopTec 1800. I'll open the first one tomorrow, after swapping all the seals.

UV dye is a good idea. I'll keep that in mind, and add to the engine oil, if the new ATF is not a very obviously different color.

RayLivingston · 08-31-2021, 12:31 AM

Ha! Just looked up the specs for the LiquiMoly. The data sheet describes the color as "brownish"! That won't be at all helpful!

RayLivingston · 08-31-2021, 12:50 PM

OMG! This is NOT fun! I've got the pan off, the connector seal out, the valve body hanging by a few bolts, waiting for it to stop dripping. With a lift, this would be a pretty easy job. Working with the car on jack-stands, it is a major PITA! I could not get the front of the car high enough to actually get under it, so I had to remove the pan and valve body lying on the ground, reaching underneath with one hand. With the exhaust pipes in the way, I could not even SEE the wiring harness connector, much less the seal tube. I had to put a jack under the trans remove the trans mount, and that gave be BARELY enough room to feel around, find the seal tube, and pry it out - completely by feel. Then I had to put the trans mount back to drop the valve body. I'll have to do the same in reverse to put it back together.

A LOT more fluid came out than on the 5HP19 on my E46 - like 2X! Good news is, the fluid did not look too bad. It was "brown-ish", but still translucent and otherwise clean.

If I had this job to do over again, I'd pay someone to do it, just because it is so difficult to do without a lift. At 68, I'm getting too old for this s**t!

mainbearing · 08-31-2021, 01:10 PM

The 335i may have a lot more plumbing causing you problems. Jacking up the car high enough and put wood blocks under the wheels or jack points was how I got to them. I got them high enough and did not remember access problems regarding height.

Not much more than about 6 qts in both the 6L45 or the 6HP19 drained out however, as IIRC just about exactly that went back in both. Yes continuous dripping was a pain.

The Liquid Moly 1800 spec sheet said brownish, but in the video it is greenish?

How does it drive now? All good?

At 35:10 into the video:

RayLivingston · 08-31-2021, 01:12 PM

Interesting! Looks almost yellow in the video. I'll go open one now, and see what color it is...

RayLivingston · 08-31-2021, 01:16 PM

Must be odd lighting in the video - it is light, translucent brown, very much like most motor oils.

mainbearing · 08-31-2021, 01:19 PM

Do make sure the valve body is correctly and evenly fastened to the transmission. That way you do not have pressure leaks past the seals.

If you do not already have this, note the tightening sequence and torque. My 6HP was a 10-bolt part:
http://www.thectsc.com/images/pdf/th...eplacement.pdf

RayLivingston · 08-31-2021, 01:27 PM

Yup, I've got my freshly calibrated torque wrench, and the tightening diagram at the ready.

Chapperss · 08-31-2021, 01:27 PM

Quote:

Originally Posted by RayLivingston

but I'm wondering if there is any other way to tell.

Transmission oil smells of cat piss - it`s horrible, still haunts me to this day......

RayLivingston · 08-31-2021, 08:47 PM

Well, this day has been a MAJOR PITA! It was a chore getting the old wiring harness seal tube out of the trans body. The new one seemed to slip into place nicely, using just finger pressure, but I could NOT get it locked into place. Nor could I remove it again! After, literally, hours fighting with it, I just got fed up and went cave-man on it. Had to break it to get it to come back out, so I just put the old one, which was NOT leaking, back in. Everything is buttoned up, except for putting all the bolts in the oil pan, and pumping in the new oil, which will be done first thing tomorrow. It that connector seal sleeve eventually leaks, I'll take it to the local (very good) indy BMW shop and let then swap it out. Shouldn't cost much, and I am NOT going to try that again without a lift.

mainbearing · 08-31-2021, 09:59 PM

If your case sleeve o-rings were red, then they will eventually leak. Mine turned mushy and the old sleeve pulled right out easily. See this post with the mushy red o-rings picture:

https://www.e90post.com/forums/showthread.php?t=1682238

The new sleeve was hard to push in, so I made sure it was properly lined up, lubed up and just pushed firmly. The two round o-rings were pretty firm and I was sure those were the problem. It was like the "last millimeter" kind of a problem.

To pull out a stubborn old sleeve on GM, I used 6" groove joint pliers, knowing there was a chance the sleeve could get crushed (but fortunately it did not). Grab onto the rim, not the entire sleeve.

https://www.harborfreight.com/tongue...-pc-64093.html

For the GM sleeve, I swapped in new o-rings (from a seal kit) onto the old sleeve; for the ZF sleeve, I replaced with a new sleeve with o-rings. Both the GM and ZF look identical but I was not risking it by swapping them. And yes I kept the old sleeves around.

In fact, if the new o-rings are still good, maybe you want to swap them onto the old sleeve and try again. You have come this far already.

RayLivingston · 09-01-2021, 12:19 PM

All O-rings are black. The old ones were still very compliant, and in perfect condition, so I just left them. They were not leaking before, they should not leak now. If they do, I'll take it to a shop, and let them spend 15 minutes swapping in a new on.

Everything is back together, and seems to be running just fine. Took 8 quarts to fill it up.

mainbearing · 09-01-2021, 01:54 PM

LOL, right, get it out of your sight. As long as it is running fine that is the important part.

08-30-2021, 06:13 PM	#1
RayLivingston Lieutenant 140 Rep 445 Posts Drives: '07 335i Sedan Join Date: Aug 2018 Location: California iTrader: (0)	How To Distinguish Engine Oil Leak from Trans Oil Leak My '07 335i has rather suddenly developed a significant oil leak, coming from the very back of the engine. From what I can see, I suspect (hope?) it is most likely the engine oil pan, but it could also be a trans leak inside the bell housing (ZF 6-speed auto trans). The leaking oil is brown-ish, so could be either engine or trans oil. Is there any reliable way to easily tell which it is?? "As we speak", I am doing the Mechatronic seal replacement on the trans, so it is about to get a fill of fresh, clean fluid, which will hopefully make distinguishing between the two sources easier, but I'm wondering if there is any other way to tell.
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08-30-2021, 06:26 PM	#2
Welcome to NBA Jam Is it the shoes!? 3884 Rep 5,112 Posts Drives: (Sold) 2011 E92 335i ZMP 6MT Join Date: Mar 2014 Location: USA iTrader: (1)	Transmission fluid is typically red in color, but the best indicator is how it smells. Transmission fluid is notoriously smelly, like sulfur.
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08-30-2021, 06:34 PM	#3
mainbearing Lieutenant Colonel 1085 Rep 1,677 Posts Drives: BMW 328i Join Date: Apr 2019 Location: LA iTrader: (0)	GM ATF uses red dye, but ZF 6 could be either amber (LG6) like engine oil or green (LG8) as I use in Audis. I would think the ATF would still be a little thinner than engine oil and would smell different too. If you are changing the mechatronic sleeve, also change out the tube seals and double-D seal, because you do not want this to happen with the cheap plastics: https://www.e90post.com/forums/attac...1&d=1502107542 My old seal was still good for the 6HP19 (Audi) when replaced along with the tube seals and the case sleeve: https://www.e90post.com/forums/showp...86&postcount=4
	Appreciate 0 Quote

08-30-2021, 07:35 PM	#4
RayLivingston Lieutenant 140 Rep 445 Posts Drives: '07 335i Sedan Join Date: Aug 2018 Location: California iTrader: (0)	Yes, I am changing the square seal, the four little round ones, and the one on the connector, along with a new oil pan/filter and bolts. Old tans oil is barely translucent brown-ish, looks and feels about the same as engine oil. Hadn't noticed any particular smell, but I will check that tomorrow.
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08-30-2021, 11:33 PM	#5
e91Owner e91Owner 425 Rep 1,129 Posts Drives: 2011 e91 & 2010 e60 Join Date: Mar 2018 Location: Out of the Office iTrader: (0)	If the replacement fluid you are using isn't MERCON SP or other red colored fluid that would make a future leak more obvious, you can always clean the area well and add some UV dye in either the engine oil or ATF to be able to tell better than smell alone.
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08-31-2021, 12:30 AM	#6
RayLivingston Lieutenant 140 Rep 445 Posts Drives: '07 335i Sedan Join Date: Aug 2018 Location: California iTrader: (0)	Don't know yet what color the new fluid is - it's LiquiMoly TopTec 1800. I'll open the first one tomorrow, after swapping all the seals. UV dye is a good idea. I'll keep that in mind, and add to the engine oil, if the new ATF is not a very obviously different color.
	Appreciate 0 Quote

08-31-2021, 12:31 AM	#7
RayLivingston Lieutenant 140 Rep 445 Posts Drives: '07 335i Sedan Join Date: Aug 2018 Location: California iTrader: (0)	Ha! Just looked up the specs for the LiquiMoly. The data sheet describes the color as "brownish"! That won't be at all helpful!
	Appreciate 0 Quote

08-31-2021, 12:50 PM	#8
RayLivingston Lieutenant 140 Rep 445 Posts Drives: '07 335i Sedan Join Date: Aug 2018 Location: California iTrader: (0)	OMG! This is NOT fun! I've got the pan off, the connector seal out, the valve body hanging by a few bolts, waiting for it to stop dripping. With a lift, this would be a pretty easy job. Working with the car on jack-stands, it is a major PITA! I could not get the front of the car high enough to actually get under it, so I had to remove the pan and valve body lying on the ground, reaching underneath with one hand. With the exhaust pipes in the way, I could not even SEE the wiring harness connector, much less the seal tube. I had to put a jack under the trans remove the trans mount, and that gave be BARELY enough room to feel around, find the seal tube, and pry it out - completely by feel. Then I had to put the trans mount back to drop the valve body. I'll have to do the same in reverse to put it back together. A LOT more fluid came out than on the 5HP19 on my E46 - like 2X! Good news is, the fluid did not look too bad. It was "brown-ish", but still translucent and otherwise clean. If I had this job to do over again, I'd pay someone to do it, just because it is so difficult to do without a lift. At 68, I'm getting too old for this s**t!
	Appreciate 1 Vivek.1367.50 Quote

08-31-2021, 01:10 PM	#9
mainbearing Lieutenant Colonel 1085 Rep 1,677 Posts Drives: BMW 328i Join Date: Apr 2019 Location: LA iTrader: (0)	The 335i may have a lot more plumbing causing you problems. Jacking up the car high enough and put wood blocks under the wheels or jack points was how I got to them. I got them high enough and did not remember access problems regarding height. Not much more than about 6 qts in both the 6L45 or the 6HP19 drained out however, as IIRC just about exactly that went back in both. Yes continuous dripping was a pain. The Liquid Moly 1800 spec sheet said brownish, but in the video it is greenish? How does it drive now? All good? At 35:10 into the video:
	Appreciate 0 Quote

08-31-2021, 01:12 PM	#10
RayLivingston Lieutenant 140 Rep 445 Posts Drives: '07 335i Sedan Join Date: Aug 2018 Location: California iTrader: (0)	Interesting! Looks almost yellow in the video. I'll go open one now, and see what color it is...
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08-31-2021, 01:16 PM	#11
RayLivingston Lieutenant 140 Rep 445 Posts Drives: '07 335i Sedan Join Date: Aug 2018 Location: California iTrader: (0)	Must be odd lighting in the video - it is light, translucent brown, very much like most motor oils.
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08-31-2021, 01:19 PM	#12
mainbearing Lieutenant Colonel 1085 Rep 1,677 Posts Drives: BMW 328i Join Date: Apr 2019 Location: LA iTrader: (0)	Do make sure the valve body is correctly and evenly fastened to the transmission. That way you do not have pressure leaks past the seals. If you do not already have this, note the tightening sequence and torque. My 6HP was a 10-bolt part: http://www.thectsc.com/images/pdf/th...eplacement.pdf
	Appreciate 0 Quote

08-31-2021, 01:27 PM	#13
RayLivingston Lieutenant 140 Rep 445 Posts Drives: '07 335i Sedan Join Date: Aug 2018 Location: California iTrader: (0)	Yup, I've got my freshly calibrated torque wrench, and the tightening diagram at the ready.
	Appreciate 0 Quote

08-31-2021, 08:47 PM	#15
RayLivingston Lieutenant 140 Rep 445 Posts Drives: '07 335i Sedan Join Date: Aug 2018 Location: California iTrader: (0)	Well, this day has been a MAJOR PITA! It was a chore getting the old wiring harness seal tube out of the trans body. The new one seemed to slip into place nicely, using just finger pressure, but I could NOT get it locked into place. Nor could I remove it again! After, literally, hours fighting with it, I just got fed up and went cave-man on it. Had to break it to get it to come back out, so I just put the old one, which was NOT leaking, back in. Everything is buttoned up, except for putting all the bolts in the oil pan, and pumping in the new oil, which will be done first thing tomorrow. It that connector seal sleeve eventually leaks, I'll take it to the local (very good) indy BMW shop and let then swap it out. Shouldn't cost much, and I am NOT going to try that again without a lift.
	Appreciate 0 Quote

08-31-2021, 09:59 PM	#16
mainbearing Lieutenant Colonel 1085 Rep 1,677 Posts Drives: BMW 328i Join Date: Apr 2019 Location: LA iTrader: (0)	If your case sleeve o-rings were red, then they will eventually leak. Mine turned mushy and the old sleeve pulled right out easily. See this post with the mushy red o-rings picture: https://www.e90post.com/forums/showthread.php?t=1682238 The new sleeve was hard to push in, so I made sure it was properly lined up, lubed up and just pushed firmly. The two round o-rings were pretty firm and I was sure those were the problem. It was like the "last millimeter" kind of a problem. To pull out a stubborn old sleeve on GM, I used 6" groove joint pliers, knowing there was a chance the sleeve could get crushed (but fortunately it did not). Grab onto the rim, not the entire sleeve. https://www.harborfreight.com/tongue...-pc-64093.html For the GM sleeve, I swapped in new o-rings (from a seal kit) onto the old sleeve; for the ZF sleeve, I replaced with a new sleeve with o-rings. Both the GM and ZF look identical but I was not risking it by swapping them. And yes I kept the old sleeves around. In fact, if the new o-rings are still good, maybe you want to swap them onto the old sleeve and try again. You have come this far already. Last edited by mainbearing; 09-01-2021 at 01:48 PM..
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09-01-2021, 12:19 PM	#17
RayLivingston Lieutenant 140 Rep 445 Posts Drives: '07 335i Sedan Join Date: Aug 2018 Location: California iTrader: (0)	All O-rings are black. The old ones were still very compliant, and in perfect condition, so I just left them. They were not leaking before, they should not leak now. If they do, I'll take it to a shop, and let them spend 15 minutes swapping in a new on. Everything is back together, and seems to be running just fine. Took 8 quarts to fill it up.
	Appreciate 0 Quote

09-01-2021, 01:54 PM	#18
mainbearing Lieutenant Colonel 1085 Rep 1,677 Posts Drives: BMW 328i Join Date: Apr 2019 Location: LA iTrader: (0)	LOL, right, get it out of your sight. As long as it is running fine that is the important part.
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