not-front-rule

Transmission Fluid leaks into Crankcase

Welcome to the Mercedes-Benz Club of America Forums
Here, you'll find members en masse who can talk, guide, answer or listen to your Mercedes-Benz related questions and comments. Participation in the forums is free to Club members. If you're a guest of this site, you'll have access to our read-only discussions. Like what you see? Join the Club to get full Q&A privileges. If this is your first visit, be sure to check out our FAQ page.  To start viewing messages, select the forum that you want to visit from the selection below.

Forum Jump

17 replies [Last post]
Guest
6ixx's picture
Offline

Posts:
6

Hello there,

I have a 1983 300D and have a problem with the Transmission Fluid leaking into the crankcase. My local mechanic can't see how it is possible (I live in rural Ontario, no Mercedes Dealers nearby).

It all began when I noticed my gears were not catching, so checked the transmission fluid, and sure enough, there wasn't much on the dipstick, so I topped it up.
Next day, I had the same problem, but there were no leaks on my driveway, and I checked to see if it leaked out while driving, but that didn't seem to be the case.
I soon noticed my temp was a little higher than normal and decided to check the oil too, which is usually right at the level it should be, but not this time... It was WAY over the max line, by about 2.5 inches.
So I ask you, oh wise and gracious Mercedes Mechanics out there, how might this be possible?

Thank you to anyone who might reply.

Cheers,
6ixx

Share this
Moderator
Maxbumpo's picture
Mount Pleasant, SC
Offline
Joined: February 2nd, 2006

Posts:
4857

Vehicles
1995 E300 Diesel
1987 300TDT
Re: Transmission Fluid leaks into Crankcase

The only thing I can imagine might be involved is the transmission cooler. I don't remember the particulars for your engine, but it is a place to start.

I hope someone else has seen this and knows the answer to the puzzle.

__________________

Max Dillon
Charleston SC
'87 300TD, 334k miles (need to pull the head again...)
'95 E300 Diesel, 335k miles (daily driving duty)
'73 Balboa 20

Member
lkchris's picture
Albuquerque, NM
Offline
Joined: January 29th, 1998

Posts:
3164

Vehicles
2007 GL320 CDI 4MATIC
Re: Transmission Fluid leaks into Crankcase

Yes, it's pretty much impossible for cross-contamination at the engine-transmission interface. Surely if this were any sort of possibilty, it would be accompanied by lots of oil also leaking to the ground in that same area.

If there is both cooling for engine oil and transmission fluid incorporated in the radiator, there could be some possibility there.

If your engine oil looks like chocolate milk, that might more likely be caused by mixing with antifreeze.

Member
shadetree's picture
Fountain, CO
Offline
Joined: August 14th, 1989

Posts:
525

Vehicles
1984 300DT
1984 230E
Re: Transmission Fluid leaks into Crankcase

Sounds very similar to the problem I had years ago with a 71 VW 411
3 door wagon. Same thing happened, that being the transmission
fluid ended up in the crankcase with little left in the xmission.
Problem was a ruptured vacuum operated transmission modulator valve.
Vacuum in that case supplied by the gasoline engine. Since vacuum
for our diesels is supplied by a pump instead I have not studied exactly
how vacuum would pull the oil from the xmission into the engine but
I suppose there could be a way. Worth a check of the xmission
vacuum operated modulator valve anyway.
Regards,
Chas Mattix

__________________

Charles E Mattix

Member
lkchris's picture
Albuquerque, NM
Offline
Joined: January 29th, 1998

Posts:
3164

Vehicles
2007 GL320 CDI 4MATIC
Re: Transmission Fluid leaks into Crankcase

Just checking ... you're aware that transmission dipsticks provide significantly different readings depending on whether oil is cold or hot? Sorry if this is obvious.

Guest
6ixx's picture
Offline

Posts:
6
Re: Transmission Fluid leaks into Crankcase

Thank you for all of your responses.

I am indeed aware of the effect that temperature has on dip readings... Thanks though.
I brought the old girl into the shop, where they pretty much thought that trans fluid in the crankcase was not the problem, dismissing the possibility. They replaced the Transmission Pan gasket and gave me an oil change. The oil DID smell and look like it was mixed with tranny fluid, which surprised them. They asked me if anyone could have done this by mistake. The answer to that is, NO, impossible. I do my own simple maintenance, otherwise, I go only to them.
I don't think the problem is fixed though. My oil seems high again and the Tranny fluid is down again. As I said, there are no leak spots on my driveway. I don't know enough to give my own opinion, but I feel certain that SOMEHOW the trans fluid IS making its way into the engine oil.
The reason I'm posting this query is to find out where this COULD happen, however unlikely, and maybe to give my mechanic a place to start looking. He is the most qualified person in town to work on Mercedes Benz. I was so hoping this was going to be a simple problem!!!?!

Any help at all is very much appreciated.

Thank you,
Alex (6ixx)

Member
shadetree's picture
Fountain, CO
Offline
Joined: August 14th, 1989

Posts:
525

Vehicles
1984 300DT
1984 230E
Re: Transmission Fluid leaks into Crankcase

Like i said on post #5. Check to see if you have a RUPTURED DIAPHRAM
IN THE TRANSMISSION MODULATOR VALVE!! And while you are at it you
might trace the vacuum line from the valve to whereever it goes, ending
up at the vacuum pump which probably dumps the tranny fluid into some
cavity in the engine block.
CEM

__________________

Charles E Mattix

Moderator
Maxbumpo's picture
Mount Pleasant, SC
Offline
Joined: February 2nd, 2006

Posts:
4857

Vehicles
1995 E300 Diesel
1987 300TDT
Re: Transmission Fluid leaks into Crankcase

I think that Shadetree has hit on a good idea - you need to check out the vacuum connections for the transmission to see if they're full of ATF.

__________________

Max Dillon
Charleston SC
'87 300TD, 334k miles (need to pull the head again...)
'95 E300 Diesel, 335k miles (daily driving duty)
'73 Balboa 20

Guest
dawette's picture
Offline

Posts:
45
Re: Transmission Fluid leaks into Crankcase

You can also add a uv dye to the trans fluid. Then run it and use a uv light to check the engine oil. No dye, no cross contamination.

Guest
6ixx's picture
Offline

Posts:
6
Re: Transmission Fluid leaks into Crankcase

shadetree;149368 wrote:
Like i said on post #5. Check to see if you have a RUPTURED DIAPHRAM
IN THE TRANSMISSION MODULATOR VALVE!! And while you are at it you
might trace the vacuum line from the valve to whereever it goes, ending
up at the vacuum pump which probably dumps the tranny fluid into some
cavity in the engine block.
CEM

Absolutely, thank you! I will look into that. I did have that down from your original post as something to check.
I also have transmission cooler written down, not sure if it applies, but there is an oil cooler part to the rad. Its definitely not coolant in the oil though, no chocolate milk.

Again, thanks to everyone for your ideas!
I'll entertain all possibilities at this point. My car is going back to the shop tomorrow, at least I'll have a couple suggestions on where to look.

This is a great site here. I'll be checking back.
It seems nobody so far has had this particular problem with a Benz. Just my luck.

Cheers,
Alex

Guest
rogo's picture
Offline

Posts:
3960
Re: Transmission Fluid leaks into Crankcase

Pull a few vacuum connections at or near the vacuum pump. If ATF is present, I would guess that the vacuum modulator on the transmission is bad. This would be accompanied by hard shifting. Does the car shift hard? If so, replace the modulator and clean out the vacuum lines.

__________________

Virginia Beach VA

87 300SDL
95 E300D

Guest
6ixx's picture
Offline

Posts:
6
Re: Transmission Fluid leaks into Crankcase

Robert Goodwin;149405 wrote:
Pull a few vacuum connections at or near the vacuum pump. If ATF is present, I would guess that the vacuum modulator on the transmission is bad. This would be accompanied by hard shifting. Does the car shift hard? If so, replace the modulator and clean out the vacuum lines.

Funny thing is, the shifting isn't that hard, seems to be no worse than usual, that is to say that the first couple shifts sometimes lag a second before catching (the engine revs a bit, then it grabs the gear), but it was almost always this way. Of course, when my trans fluid is very low, it has trouble catching the gears at all, feels like the car is gutless.

I can say with reasonable certainty, that the trans fluid drops quickly. I poured 2 liters into the tranny, took a 10-15 minute spin, rechecked the levels and its gone! Checking the oil dipstick, the increase there was obvious.

Still, I'll check the lines as you suggest. Thanks

Guest
6ixx's picture
Offline

Posts:
6
Re: Transmission Fluid leaks into Crankcase

Well, I have to say, THANK YOU, to everyone who took the time to respond to my query here.

It did turn out to be the transmission modulator valve!
Still, I was surprised at how fast the trans fluid emptied into the engine oil through this valve! And the car shifted fine, no hard shifting at all.
Its fixed now, and I'm relieved.

This is a great forum here. A great resource.

So, thanks again!

Cheers,
Alex.

Guest
rogo's picture
Offline

Posts:
3960
Re: Transmission Fluid leaks into Crankcase

Consider yourself fortunate that you weren't driving an old VW 411. There is one hose that would come off and cause all the fuel in your tank to try to fit into the crankcase. If you continued on a long drive, I guess the thing would have turned into a fireball.

Luckily, ATF has a much higher flashpoint.

__________________

Virginia Beach VA

87 300SDL
95 E300D

Member
shadetree's picture
Fountain, CO
Offline
Joined: August 14th, 1989

Posts:
525

Vehicles
1984 300DT
1984 230E
Re: Transmission Fluid leaks into Crankcase

Never had a problem with my 71 VW 411 leaking any gas. Just the failure
of the transmission modulator. Considering the extended use of the 411
during the years 73 thru 76 running all over Europe guess I was lucky
that the gas hose didn't give out. Even pulled a small camper over the
Great St. Bernard Pass between Switzerland and Italy. Finally had the
problem with the xmission modulator valve after bringing the 411 to
the USA.
Regards,
Chas Mattix

__________________

Charles E Mattix

Guest
rogo's picture
Offline

Posts:
3960
Re: Transmission Fluid leaks into Crankcase

Actually, it wasn't a gas hose issue. It was vacuum and what I described was the worst case. Best case, a little gas went into the crankcase. Most people never knew it and had the problem fixed because it affected performance in some way.

__________________

Virginia Beach VA

87 300SDL
95 E300D

Member
pch2021's picture
Rockledge, FL
Offline
Joined: September 15th, 2005

Posts:
2780

Vehicles
None
Re: Transmission Fluid leaks into Crankcase

Wow, I was a little late on that, but that modulator valve is certainly responsible.

__________________

Pierre Hedary
...happily servicing vintage Mercedes-Benz in sunny Florida...
1972 280SE 4.5 252K
1970 280se 3.5 coupe 108K
1971 300sel 4.5 121K
1991 420SEL TMU, but looks brand new!
Mercedes technical advice: 407 765 2867

Guest
6ixx's picture
Offline

Posts:
6
Re: Transmission Fluid leaks into Crankcase

Well I was getting pretty concerned that this problem was going to be the end of my 1983 300D, my confidence in her was wavering, but with the advice on this board, she has got a pretty good chance now to roll over the 400,000 Km mark. She's at 360,000 now. I had the timing chain done a couple years ago. I think I'll be looking on this forum for more ways to preserve the old girl. I guess she is considered a classic now, being 25 years old.

Cheers,
Alex.

Forum Jump

Share this