Resealing OM617 Oil Pan, Turbo Oil Return Line, and Air Cleaner (Blowby) Drain

[deniss]

As I was about to perform a routine oil change on my 1984 300SD, I noticed that the allen bolts holding the lower oil pan are soaked in engine oil, especially on the driver side.

After cleaning the oil pan and the area around it with a degreaser and a slim bottle brush (mine had enough grime there to plant a potato field, it seemed like), I determined that both the lower oil pan gasket and the rubber grommet at the bottom of the turbo oil return line are due for replacement.

I decided to also take care of the o-rings for the oil separator drain tube, which drains any blow-by oil from the air filter housing and into the oil pan -- right behind the turbo oil return line.

To prepare myself for what to expect, I first consulted the following threads:

-- Dave Morrison's write-up with pics
-- Shell's write-up with pics
-- whunter's thread with pics
-- How is the oil separator drain tube mounted?
-- Another thread about oil separator drain tube

Before you read my tips and comments on the repair, at least have a look at the top 3 links above -- they offer good pictures of the parts and the engine area where you'll be working, as well as list dealer part numbers for the relevant parts you will need to buy.

I don't have a garage, so I did all the work outside, on a parking lot, with the car up on the ramps. You spend most of your time under the car for this job, except changing your oil filter and removing your air filter housing assembly.

If you don't have a shop light or some sort of portable lighting, now is a good time to invest in some. I bought a rechargeable 30-LED shop light at Walmart for $20. I thanked myself many times over for this investment. I also found it very useful to have a runner's headlight strapped to my head for this job: it's just an LED light mounted on an elastic headband.

Also, Walmart's paint department sells plastic-lined covering cloth. Consider it your "shower curtain" for this job -- it's good and cheap, and you will need it to catch the oil drips once the oil catch pan is removed. Just lay out the covering under the oil pan area and secure the four corners with something heavy so it doesn't move around.

Recommended Prep:

- Drain the oil the night before to minimize the oil drip when you remove the oil pan (oil pump will still drip a bit of oil no matter what, but it helps minimize the drip).

- Soak the rubber grommet (617-187-01-85) and the o-rings (004-997-53-48) for the turbo oil return pipe in some non-synthetic oil, like a Delvac 1300, to get them to be more pliable and easier to seat. Those genuine MB o-rings and grommet are beefy, and you need all the help you can get working them in.

- Remove the air filter housing assembly to get extra light and space.

1. Oil separator drain (from the air filter housing to the oil pan) is secured to a bracket under the turbo by a 10-mm bolt with a nut. This nut is exposed to a lot of heat and is rust-covered, so apply PB Blaster on it several times the day before you do this job!

A few folks here have said their oil separator drain tube isn't secured by anything and is therefore loose (due to either a missing bolt or a broken clamp that's supposed to be welded to the drain tube). Get in there with a little telescoping mirror and inspect. If the bracket is still there and intact but the bolt is missing, please do secure the drain tube after you're done replacing the o-rings. When left unsecured, these tubes thrash around and will eventually wear a hole and leak, so it's in your best interest to secure it. The tube is supposed to be secured on the engine side of the bracket.

The oil separator drain tube on my car was secured in place, with the clamp intact and the bolt through the bracket with a nut facing the right side of the vehicle. The nut and the bolt were covered in rust pretty badly, so I blasted them with PB several times the day before and the morning of.

To remove 10-mm nut securing the oil separator drain tube, I conjured up the following "tool":



I have a 10-piece Craftsman "midget wrench" set, which are the tiniest wrenches available up to size 11mm. I used the box-end 10-mm wrench from this set (pictured) as a counterhold on the bolt facing inward. You will want to snake your left hand through the steering tie rods and from behind the engine to put a finger on the bolt head to keep the wrench on it -- the turbo/exhaust manifold above will act at the counterhold as you turn the nut. You just gotta keep that wrench in place with your finger.

To turn the nut, I used a 5/8" Crescent box-end on a "stub adaptor" plugged into a 10-mm socket. Yes, I'd rather have a small ratcheting gear wrench to turn the nut, but this is what I had at my disposal, and it did the job. A crawfoot line wrench would be useful here and should fit the space well, but I didnt have it at my disposal. Just whatever you do, do not use a standard open-ended wrench on either the nut or the bolt -- you will strip it, and then good luck.

The nut broke free easily but undoing it off the rusted-over bolt was the annoying part and required a LOT of torque. I kept applying PB blaster along the way and managed to remove the nut without even damaging a thread.

Once the nut is off, you can lift the drain tube off the nipple above the oil pan and replace the o-ring on the nipple. The dealership wasn't able to find these o-rings on their parts diagrams, so I went to the hardware store to an those o-rings (need 2 -- one for the nipple on the air filter assembly, one for the nipple above the oil pan).

I now cannot remember the size of o-ring that works, but it wasn't 10mm (od) x 6mm (id) that was suggested in one of the threads above. I suggest removing an o-ring from the air filter assembly nipple and taking it to the hardware store to match (both Lowe's and Ace Hardware have good o-ring selections).

When I re-secured the oil separator drain tube, I installed the brand new stainless steel nut and bolt of the original size/length, to prevent rust build-up. (I took the old bolt with me to Ace Hardware and had it matched there -- I think the bolt is designated M6).

2. Turbo oil return line: disassembly and removal of old grommet. The turbo oil return line consists of two parts: the upper pipe that mounts to the turbo by two 13-mm bolts and the lower pipe that drains into the oil pain and is secured to the engine block by a rubber grommet. The lower pipe has an o-ring on each end, and the upper pipe is flared at the bottom where the lower pipe fits in with an o-ring.

My rubber grommet at the bottom of the lower drain pipe was hard as a rock -- no surprise it was leaking. I tried to pry the old grommet up out of its seat, so I could push the lower pipe all the way down into the bore and hopefully clear the upper pipe, so I could remove the lower pipe without having to unbolt the upper pipe from the turbo.

That didn't happen, as the lower pipe simply wouldn't go down far enough. So I had to first unbolt the upper pipe from the turbo and remove it.

There are two 13-mm bolts on the oil return port of the turbo -- they are clearly visible from underneath the car. I used a standard ratchet with 3/8" driver, a 3-inch straight extension, and a short 13-mm socket. There was enough clearance for doing this, and the bolts broke free without trouble -- just keep those sockets at 90 degrees to the base, so you don't round out the bolts when you apply the torque.

In the threads above, some folks mention using long extensions and universal joints to snake your way to those two bolts on the turbo -- I found this unnecessary.

With the upper pipe off the turbo, you can remove it by tilting it sideways toward the right front corner of the car (the lower pipe will move in its seat enough to give you wiggle room to operate).

Next, I attempted to remove the lower pipe out of its seat. I pushed, and I pulled. I decided that if I didn't try some other method, I would probably get either hemorrhoids or hernia by the time this is over. So, I strapped two hose clamps tight around the pipe and used a pry bar to pull the pipe out of its seat. No dice -- it wiggles in there but won't come out!

I decided it's time to pull the oil catch pan and see if I can drive that pipe out from below. Removing the oil pan is very simple (just make sure you pre-clean this area beforehand is there's a lot of grime). The oil pan is secured by a bunch of 5-mm allen bolts. For the love of Pete, use a good quality allen wrench with a ratcheting driver and make sure the wrench is seated nice and deep in each bolt's hex pattern. You don't want to strip these allen bolts.

With the oil pan out of the way, you can see the end of the turbo oil return pipe from below. I picked a deep socket out of my tool set that's just smaller than the bore and drove the lower oil return pipe out by hammering on the socket from below. It took a lot of force to drive that pipe out, but there was absolutely no damage to the bore and no damage to the pipe, so don't be afraid to use this method if you're faced with the same situation.

Some folks here have said they were able to pull the pipe out without having to drop the oil pan and drive it out. Either I got unlucky or some folks here have enough strength to lift a car. Some folks here have also said that this lower return pipe is rather soft and easy to damage. I didn't find that to be the case at all.

With the pipe out of its seat in the engine block, you can remove whatever was left over from the old grommet and clean the bore.

3. Cleaning the oil return port of the turbo from the old paper gasket is the next step.

To prevent crud/shavings from getting into the exposed engine underbelly (oil pan is out!), I recommend temporarily re-installing the oil pan (with the old gasket or no gasket at all) using just two allen bolts across. You also recommend covering up the bore where the lower oil return pipe used to sit with some foil while you clean the turbo port directly above.

Here is all you need to clean the old paper gasket off the turbo oil return port:



This blade is really the best possible tool for cleaning the turbo oil return port. It's sharp enough to pick the old gasket out and small enough to get into the space available. You have to clean the turbo from underneath the car, and you have a clear view of the port from underneath with a shop light. Make sure you polish the port real good with that blade and get all of the old gasket out, or it will leak, and you know you don't want to be re-doing this job.