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While working on the oxygen sensor I noticed that the rubber plug next to the oxygen sensor connectors is slowly sipping oil. There is also a small oil stain on the protective shield. What is this plug for? Is it the transmission assembly I am looking at? How do I fix this leak? It looks like a converter housing gasket A211 271 01 80. Thanks.
If it is the torque converter leaking, then I wonder why. Was it drained and filled recently? Then perhaps the drain plug is not secure? Or could it be a leak coming from further forward of the car? I believe the gasket is just a cover than can be easily removed. If so, you may want to take it off and look inside. Also I would suggest checking the transmission fluid level if possible.
I have this car since December 2018. I did not do anything with the transmission. The previous owner had transmission oil replaced at the dealer in January 2018. The car has only been driven about 13K miles since then. Looks like the plug inside is not secure or the o-ring is damaged. Can I replace this o-ring (and possibly the inner plug if needed) by partially draining the transmission (only draining the torque converter) and then adding some transmission fluid? How do I check for the proper transmission fluid level in this car? I read that I need a special dipstick, a new cap, a new cap locking tab, and a thermocouple probe to make sure the fluid is at 175 F and the engine is running. Is this the right procedure? Thanks.
That sounds right. You can probably skip the heat probe, just let the car warm up, either by driving or letting it idle for awhile. Or use a laser themometer to spot check a few areas of the transmission (pan). Check out fluid change kits from FCPEuro. They have everything you need. A few tips. As far as I know, the dipstick does not go all the way in. Check the fluid when the engine is running and has warmed up. Once you've hit the level that satisfies you, later on when the engine is cold, take a cold level reading. I did this is to make sure the reading I got when hot was the correct reading. This took me a few days of checking, but I wanted to make sure the level was correct. So I started a bit underfilled and slowly added fluid until I was satisfied the level was sufficient. Now the transmission shifts smooth.
Typically a dealer will drain the transmission from the transmission drain plug, not from the torque converter. If done from the drain plug, the amount drained is roughly 3-4 quarts. But if drained from the torque converter, you can expect at least 7-8 qts, if not higher. In any case, doing a drain and refill is not that hard. Just takes a bit of preparation to have everything ready.
As far as the type of transmission; I believe you are correct it is 722.6. By 2008 MB had switched to the 7 speed 722.9 for most of their rear wheel drive cars, however I think the 4Matic stayed with a version of 722.6. Therefore the fluid is still ATF134? Somebody please correct me if I am wrong. Putting in the wrong fluid would be very bad. Please triple check before proceeding.
Thanks for the reply. I took the torque converter gasket off (part# A211 271 01 80) . It fell apart in my hands, and it had oil on the inside. Then I spun the engine by hands with a 27mm socket and looked at the converter. The converter does not have a drain plug. Instead it has a welded strip on one side. The opposite side is solid, but has similar round marks. So, it can't be the o-ring problem I thought, because there is no bolt with an o-ring.
Somehow, an oily fluid (transmission fluid?) gets into the compartment behind the converter gasket. The gasket is not tight, it has a hole in the center by design.
What do you think the problem is? What are the ways that oil can get into the compartment behind this gasket? One option would be a damaged welding strip. Why is it even there instead of a normal drain plug? Visually, I did not see anything, but the seepage is very slow. Is this strip needed for balancing? Is the drain plug located under that strip?
Are there other likely ways for the oil to get into that compartment? Where would a torque converter leak? Is there anything inside that compartment that could be leaking?
The torque converter I have is part # A2092500602.
Thanks,
2025 AMG E 53; 2018 GLC300 4Matic; 2003 360 Modena
Most likely - that leak is from the rear main seal. Given how slight it is, it's not worth fixing. The rubber plug is really just for dirt and dust - it's not meant to be any kind of a fluid seal - trans or oil.
It is possible it may not be transmission fluid. I think the gasket location just happens to be one of the lowest and rearward point of the car. It could be an engine oil leak. These are much more common. I have had similar wetness at the exact same spot on my 05 E320 (M112 engine with 722.6 trans). After replacing the valve cover gaskets, I still had wetness and I thought it was the rear main seal. It turned out to be a cracked oil level sensor located on the oil pan. Anyhow that was my situation. I would suggest cleaning everything off very thoroughly and then go for a short drive. Then take a look again to see where there is wetness. If the welded spot was leaking, I would assume there would be fluid everywhere as that part rotates. Touch the oil pan and the pan gasket. All dry? If it indeed is the rear main seal, that can be a big job. Also, check your engine oil level. Do you know the procedure on how to get the total oil quantity reading? Not sure on your particular year, but for me it was to turn key to On position (just before the starting position), then press the trip meter button twice. This gets me into a more detailed mode on the screen.
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