Catch can vs. Oil separator - PeachParts Mercedes-Benz Forum

fezcabdriver · #1 12-14-2016, 02:20 AM

I recently picked up a truck with an om617 engine. The air filter doesnt have the oil separater. Instead, the tube from the valve cover just points to the ground. Am I missing something or can I fix some sort of bottle to catch the oil and pour back in or discard during oil change intervals?

Rogviler · #2 12-14-2016, 02:27 AM

Mercedes did all manner of things with blow-by oil at various points, so you can kind of take your pick. I have too much to just dump it on the ground, and I've never liked the idea of it going directly back into the intake (that's one possible way a runaway can happen), so I went the catch can route. It wasn't hard to make my own and have it drain back to the oil pan via the original drain for the air cleaner. Then the clean vapor is vented.

I used a couple of ABS caps cemented together with a baffle inside made from ABS sheet and bronze wool as additional baffling. Works much better than the catch can system I had before, which was purchased. If you do purchase one, make sure it's big and has some kind of baffling inside.

-Rog

fezcabdriver · #3 12-14-2016, 02:30 AM

Thanks. Do you have any pictures?

Dan Stokes · #4 12-14-2016, 07:52 AM

I use a commercially available catch can - standard hot rod stuff. I'd post a pic but I already posted it in my build thread and the forum format won't let me repost it. Check out my build thread (search for my name) and you can pull it up. I have both my crankcase and valve cover breathers plumbed to it and it seldom has anything in it when I open the drain. So at least in my situation it works great - but I only drive maybe 25 miles per year..

Dan

Mxfrank · #5 12-14-2016, 10:32 AM

The proper way to dispose of crankcase gas is to route it to a low pressure area. In ancient times, it was routed through a draft tube...which is what you seem to have. The draft tube simply routes to a point under the car where air pressure is relatively low. In the pollution control era, the crankcase is vented to a low pressure point in the intake system, so that unburned fuel and oil can be consumed by the engine.

The idea is to maintain a slightly reduced pressure in the crankcase, to prevent seal leakage. For some reason this will also increase engine output a bit. Running it to a catch can will control vent oil loss, but will increase pollutant release by about 25%. Quite a bit of that will find it's way back to the passenger compartment, so enjoy.

mach4 · #6 12-14-2016, 10:46 AM

Quote:

Originally Posted by Dan Stokes

I'd post a pic but I already posted it in my build thread and the forum format won't let me repost it.

It's very easy to do....don't try to repost the image, just link to it.

- Click on the image so it comes up in its own web page
- Highlight the URL in the browser
- Copy it
- In your post editing window enter the text "[img]"
- Paste the URL you previously copied
- Enter the text "[/img]

And even easier is to click the image icon and paste the image URL like thusly

Dan Stokes · #7 12-14-2016, 12:37 PM

Uh, OK if you say so. You have no idea what a computer illiterate you're talking to!

What I've tried in the past is to go to my file of pics, pull up the pic, and post it. That's when it gets rejected.

Dan

fezcabdriver · #8 12-14-2016, 01:07 PM

Thanks for all the replies. So upon further inspection, it looks like the previous owner closed off the return drain inlet above the oil pan. Not sure if this was done because the air filter was not stock or if the check valve was not working and a replacement couldn't be found. Let's assume the check valve is not working. If I make some sort of separator can that drains the oil into a bottle and not back into the drain pipe, does anyone see anything wrong with that? Pollutant wise?

mach4 · #9 12-14-2016, 01:41 PM

A catch can works just fine. Too bad the drain into the crankcase was blocked off as you could just have the oil drain back into the pan from the catch can rather than have to drain it periodically.

Some have adapted a fitting on the turbo drain line to allow the catch can to drain into that on engines without the port on the top of the upper oil pan.

kerry · #10 12-14-2016, 02:10 PM

What kind of truck did you get with a 617? Not many MB trucks used that engine as OE. They did put it occasionally in the smaller vans which typically had the 616. Can you post a picture?

fezcabdriver · #11 12-14-2016, 02:27 PM

1994 4Runner with om617.951, 5speed, 4x4, and super duper slow. I'm thinking that I need to clean out the banjo/alda thing but since the draft tube was leading to the floor, maybe there is no soot in the banjo and I have to accept the fact that it is slow. It does have the egr still in place though.

kerry · #12 12-14-2016, 02:57 PM

It really shouldn't be that slow. How much does the truck weigh compared to an SD? Seems they must be comparable. Have you measured the boost?

fezcabdriver · #13 12-14-2016, 03:05 PM

The 4runner weighs 200 more lbs.. plus it has a beefy bumper, bigger tires 31". Not sure on the weight savings regarding the difference of 4runner auto tranny vs. what is in there now 4runner manual and transfer case. Maybe I need to explore gearing at some point.

It has a boost gauge but in truth, I don't really know much when discussing turbos and need to read up. The gauges installed on the pillar are for exhaust, turbo, oil pressure, and all read in PSI and not bars. I'll probably start a new thread on the forum later on after I read up and have questions.

kerry · #14 12-14-2016, 03:10 PM

I don't have a boost gauge on my MB. My 93 GMC 6.5 puts out about 10psi max.

Graham · #15 12-14-2016, 03:17 PM

Quote:

Originally Posted by mach4

A catch can works just fine. Too bad the drain into the crankcase was blocked off as you could just have the oil drain back into the pan from the catch can rather than have to drain it periodically.

Some have adapted a fitting on the turbo drain line to allow the catch can to drain into that on engines without the port on the top of the upper oil pan.

The engine in my 85 300D came out of an early turbo 300SDL. The guy that installed it said that there was no drain fitting that would allow air cleaner pot to drain back to sump. He put a plug in the nozzle in the bottom of the air cleaner. I found that out when it started leaking.

I put in a new plug, but also drilled a hole in the oil separator lid and installed a screw-in cap. When I do an oil change, I remove that cap and suck any oil that has collected out during oil changes. However, oil mist and droplets hopefully mix with lower pressure incoming air and get burned.

More or less a catch pot with a vent into the air intake. That should be something fezcab could do.