om617 rear main seal question
 

i ran my car in the driveway today to work on the vaccuum locks which nothing is wrong with them at all but i ran it for 5 minutes and then shut it down.. i just walked by and noticed a small fresh oil spot the sized of 2 quarters next to each other...

it looks like its dripping from where the transmission mates with the engine. the whole back of the block is coated in an oily sand like crud but the front isnt nearly as bad.. is this the rear main seal going or the person who put the new transmission in fault? if i can get the place from the p/o that put the tranny in to fix it because it is their fault ill live but i dont want to take the whole engine tranny out for a stupid seal.. but if it has to i will as soon as i can

are you sure it is the rear main?
 

sure it is in fact engine oil? black? not reddish?

the rear mains dont often leak.

tom w

it is black

Sure its not the valve cover gasket leaking in back....of the oil filter housing gasket at the block?

ill check those out... i bet it could be the valve cover seal because both sides are covered. i just need some $$$ to get parts and crapola

this car still isnt registered im waiting for the title in the mail form the p/o

Degrease the engine....will make finding oil leaks far easier.

It IS the seal
 

When they changed your transmission they unbolted the rear transmission mount and cross member allowing the transmission to hang down unsuported for esier acsess to the bell housing bolts this I have learened twice causes the rear main seal to leack also if you pull the engine and transmission and dont block the transmission so it is leval with the engine when you seperate them it will cause the seal to leak. Replacing the seal is no big deal about $10 and over 40 hours of labour, Your leak may be small enough that the stop oil leack additives that rejuvinate seals and are only to be used for a hundred miles before changing the oil do work some times you should disconectt your crankcase vent hose from the valve cover leaving the hole in the valve cover open to vent into the engine bay this will reduse the crank case pressure stopping the leak from getting bigger till you try the oil additave or and good luck with this one get the transmission shop to pay well over a grand to fix there screw up. I left a transmission hanging unsuported for a month the seal leaked a quart a day but with the vent tube off it barely dripped I left one hang for ten miniutes to get at the bell housing bolts eiser it sprung a small leak that stop leak fixed I bought two other cars that developed leaks right after they had used transmissions installed and leaked I got them for a song and with the vent tube disconnected and oil additive for a hundred miles they never leaked again

ill remove the vent thing.. also i dont know if she is running dino oil or synthetic... when i change the oil ill put in some dino motor oil.. i dont know what brand but ill research and put some additives and such..

Don't remove the vent
 

I'm looking at replacing my rear main seal as well, so any information is appreciated. I'm planning on just dropping the transmission, I hope everything is accessible from underneath the car with the transmission out.

I would advise against removing your vent host though. The host recirculates fuel fumes into the intake, and oil blow-by back into the case. If you pull it off, you're probably going to have an oilly mess all over your engine bay.

-Colin

I agree. My air cleaner has a lot of oil in in (working on this now) from that tube....i def. woudlnt want that all over the compartment.

i bet my oil is leaking from the valve cover.. the whole back of the block is saturated with oily crud... from the top down.. and when i start the car and let it sit then shut if off a lil drip of oil comes off where the tranny and engine meet up

this isnt the OG tranny its a rebuild..

degrease it when you can...do not spray the IP on a hot running engine or you will regret it...


and old toothbrush will help with the heavy crud...

Yea I agree to degrease first and then assess. It might be your oil filter housing.

several toothbrushes....helped when i did it and she's still a greasy mess! (front and rear of the block)

not as bad as a quart a day
 

You cannot change the rear main crankshaft seal on the Mercedes with out removing the engine. The seal is held in place by 2 pins so there is no way to rope a new seal to the old and pull it through. You really have to remove the engine from the car. You must remove the upper oil pan to replace one-half of the seal. Then you must remove the crankshaft from the block. Now you can install the seal, which I believe we paid less than $4 for from the dealer. Now you’re confronted with the dilemma. Do I replace the bearings since the cranks out, shouldn’t I replace the ??? While the engine is apart.
With the crankcase vented straight in to the engine compartment, this relived enough backpressure in the crankcase to stop the quart a day leak. However, it did cause about a quart of oil a month to blow a very fine mist of oil on everything under the hood. At this point, I was very happy because you cannot really drive a car that leaks a quart of oil in less than 20 miles not to mention the mess it leaves when you park it. But a quart of oil a month out the breather hose is a breeze to clean and could also just be renamed from crank case ventilation to automatic corrosion control system another Mercedes engineering first.
I had some luck using a product called trans X on transmissions and looked for a similar product for engines. I don’t recall the brand but one product was very specific it could only work on old dry seals and gasket material it could not rebuild your engine. I spent 8 bucks on a can. I added it to the oil with the breather hose still disconnected I drove the car for the recommended 250 miles then changed the oil and reconnected the vent tube and no more oil leak. Since then I have had 3 other occasions dealing with different Mercedes W116 and W123 rear main seal leaks where this method has been very beneficial and saved the cars from the scrap heap.
It cost $6 for enough oil leak fluorescent additive to find all the leaks on several cars. Cleaning up oil grease and gunk is great it especially makes working on them more pleasant. However, do you want too properly detail your engine or do you want to find and fix the oil leak ASAP. For $6 you will know definitively where the leak originates in under 5 minutes leaving, you time to actually fix the problem rather than chase I choose to buy the florescent oil leak detection additive .
Dave S
:)