I'm removing the lines from the oil filter housing in order to change the block to housing gasket. I've removed the lines before on other cars and I've never had to use a backing wrench on the housing to break the oil cooler line free. This time around the top one broke free easily, but on the bottom one the fitting that threads into the hose from the filter housing is rotating with the hose. I'm going to try to get a thin 24mm? bicycle wrench to put on that fitting, but I'm wondering if I've done serious damage to the threaded fitting on the oil filter housing, it was leaking a little bit previously. Thanks

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'81 300SD

It depends on how much you turned it. You will not know till you take it off.

That particular fitting is sealed by a Cush Washer. The threads on the Oil Filter Housing end are 18mmX1.5 which happens to be the size of some of the older Spark Plugs and places like OSH Hardware sell Taps that size.

Since it is a Spark Plug size if the worst has happen there is likely a thread repair kit for that size.

Mercedes sells new fittings for about $12 each or you can easily remove one at a junk yard.

When you install the Fittings to the Oil Filter Housing you can use Red Loctite on the degreased threads of both (I use brake cleaner for that) and that should keep them from backing out the next time. To remove them you can heat the housing with a Propane Torch and that melts the red Loctite and they can be removed.

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84 300D, 82 Volvo 244Gl Diesel

Ohhh...you never want those fittings to come loose from the oil filter housing....This is why the FSM says to use "two" wrenches when removing them.....See the same thing that happens with the oil cooler nipples threads breaking can happen to the oil cooler threads.....This will then start a horrible leak that is a PITA to fix...using lock tight to secure the coupler into the oil filter housing is a cross your fingers and hope situation....As it can squeeze out and block stuff in the housing....Ask how I know all this :p

Get the right size wrench at a el cheap tool store and simply grind it down to the right thickness....easiest way to get a wrench to fit on that....

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Meh, I had the nipples break free from the oil filter housing as well.

On mine they weren't all that tight anyway. I got a thin 24mm wrench to tighten them back up and hold them as I backed the oil line off.

It's all fine, it doesn't leak a drop on mine, so I think you're most likely fine.

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"The MB W123 is so bulletproof, you can drive them forever. Which is a good thing as it takes that long to get anywhere."
Betsie: 1984 W123 300D (hobby, 280k miles)
Myrla: 2001 Mazda Protege 2.0 ES 5spd (daily driver, 130k miles)
The Turd: 2007 Toyota Camry (wife's car, 118k miles)

I was able to fit a 15/16" craftsman wrench on the fitting and get that second cooler line off. When I turned the first Allen bolt to loosen it, it was really loose. That bolt on the top left corner behind the lines is hard to get at without removing the oil cooler lines, so I hadn't tightened it up like I did the other 4 a few months ago. I loosened all of the Allen bolts, then torqued them back up as evenly and as tight as possible. I took the car for a short spin on the highway and it appears as if the leak is gone. The oil cooler and lines were hot, so I think that the gasket was tested. We'll see how long my "fix" holds up.

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'81 300SD