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'82 240D 4-spd
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I was going to re-assemble the oil filter housing today and was examining the cover assembly. I noticed the small port up near the top of the cover and looked up the oil flow diagram. Turns out this is for the return of "fine filtered" oil to the oil pan. Well, I checked to see if there was flow through this pipe using some carb cleaner, but it was clogged up tight. So I shot cleaner into the other (large) end and let it sit, repeated the operation from the small port, did this a few times and then hit it with a blast of compressed air; at this point the fluid went through and out the end of the pipe. Seemed good.

But...turns out the fluid goes the other way through the pipe now also! According to the attached diagram, this is supposed to be a one-way flow, from the top of the pipe out the bottom, and there's a check valve (#19) to keep it that way. I suspect the check valve is either stuck or busted.

It appears from this diagram that the bottom of the pipe may be removable and allow access to the valve; my attempts to open this (assuming it's threaded) so far have been fruitless, and I don't want to cause damage to the part. I may try a little heat, but I'm gonna play it conservative.

So I have the following questions:
1) Has anyone ever had that end of the pipe disassembled? If so, what was the process?

2) Do y'all think that bi-directional flow is probably not a problem, as long as the pipe is open? Or do you think that crankcase pressure will end up pushing crap back up the pipe if the check valve isn't working?
 

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1984 300D
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Take a close look at the picture and you will see there is a spring loaded 1 way Valve in the Tubing.
The direction of flow is towards the Oil Pan.

I have never attempted to access the Valve but I did find out that the tube; at leas on mine can be pulled out of the upper Cap. That Tube is only pressed in.

Also the upper portion of the majority of different makes of the Oil Filters is full of waste raw cotton fibers and contains various degrees of plant parts.
I have read at least one account where there was Cotton caught in the Valve and holding it open.

I have no idea how to access that Valve I have always though the tip must be made in 2 sections screw together but you would need something with Aluminum Jaws to grip it so I have never bothered to try.
 

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