Air oil separator options - PeachParts Mercedes-Benz Forum

Cadin · #1 06-18-2014, 12:27 PM

Hey All,

I'm looking to modify/swap my air box to stop the rattle/gain more air flow (is this possible/needed), and to have the crankcase vapor captured and returned to the sump as neatly and robustly as possible.

Here is my current plan:
Since the engine is in an 1992 FJ80, I am thinking of going with the stock FJ80 air filter (4.0 gas engine); but I don't know if flow will be sufficient. The FJ80 stock air filter mounts on the right fender, and I was planning on using something like this:

http://www.aircraftspruce.com/catalog/eppages/hboilbreather.php

to separate the crankcase gasses and drain to the sump. Does anyone know of a better/cheaper/easier/more robust option?

What do you guys think? Is the stock air cleaner high enough flow that I am better off with it and not needing to mess with fabricating new a oil return system? (I can open up the intake to the filter.) Is there a 3rd party/Junkyard/Other option for a sufficient sized air filter with relatively inexpensive replacement elements?

(Either way I plan on pulling air from the stock right inner fender (Cold Air) location since it is in the trough of the bow wave for water crossings, so initial air temp shouldn't be a factor; no open cone filters here!)

pawoSD · #2 06-18-2014, 12:45 PM

The stock air cleaner on an OM617 has more than enough airflow for the engine's needs. Remember its an MB engine, they tend to "overengineer" rather than the other way around...

mach4 · #3 06-18-2014, 12:54 PM

Quote:

Originally Posted by Cadin

Hey All,

I'm looking to modify/swap my air box to stop the rattle/gain more air flow (is this possible/needed), and to have the crankcase vapor captured and returned to the sump as neatly and robustly as possible.

Here is my current plan:
Since the engine is in an 1992 FJ80, I am thinking of going with the stock FJ80 air filter (4.0 gas engine); but I don't know if flow will be sufficient. The FJ80 stock air filter mounts on the right fender, and I was planning on using something like this:

HOMEBUILDERS OIL BREATHER/SEPARATOR from Aircraft Spruce

to separate the crankcase gasses and drain to the sump. Does anyone know of a better/cheaper/easier/more robust option?

What do you guys think? Is the stock air cleaner high enough flow that I am better off with it and not needing to mess with fabricating new a oil return system? (I can open up the intake to the filter.) Is there a 3rd party/Junkyard/Other option for a sufficient sized air filter with relatively inexpensive replacement elements?

(Either way I plan on pulling air from the stock right inner fender (Cold Air) location since it is in the trough of the bow wave for water crossings, so initial air temp shouldn't be a factor; no open cone filters here!)

First on the air cleaner front, you'll be just fine. When I did the air cleaner on my 717-> 107 swap I originally did it using a 250cfm air cleaner. The stock 617 one flows about 450 cfm. Using a really, really dirty filter that came with the unit I got at the junk yard, the restriction wouldn't even register using a filter gauge used to measure restriction. Shortly after I found a 350cfm filter that would fit my custom air filter bracket and have been using that. The MB filters are engineered way, way over what's needed, likely to ensure adequate flow even when extremely dirty.

Your catch can strategy should work just fine. I built my own consisting of a rectangular box with baffles and filled with stainless steel wool. The "clean" vapors go back to the intake and the condensate drains back to the pan (I have an early "smooth" pan with the port for draining oil condensate back to the sump).

The aircraft catch can is likely pretty expensive. A search for "catch can" on eBay will give you a fair amount of options that are quite cost effective and may do what you want.

If you don't have the drain to the sump you can use a catch can that has a drain petcock on the bottom and just be sure to drain it periodically.

Quote:

72% 1992 FJ80 + 17% 1983 OM617 + 10% 85/87/92 4Runner + *Eclipse/GMC = 100% Truck
(*<1%)

Is that by weight or volume?

Simpler=Better · #4 06-18-2014, 12:57 PM

I imagine the stock 4.0L filter would be fine as well, you're not running at full boost all the time. Definitely run some kind of oil separator, or replumb it back into the turbo. If you use a vent tube you will have a huge oily mess (don't ask how I know)

mach4 · #5 06-18-2014, 01:43 PM

Let the record show that the stock filter will flow more than enough...

Cadin · #6 06-18-2014, 09:52 PM

Wow, you guys are awesome! (And quick!) It's good to know that either filter is sufficient; thank you for the actual numbers! The both leave some room for dusty roads and the like. (The Landcruiser even has a pre-filter debris catch on the bottom that can be emptied independently of the air filter!)

I think that separator was ~$50 IIRC; is that expensive for such a robust unit? I shall check the 'bay. (I definitely plan on recollecting the oil, if only I could get the rest to stop dripping...!)

Cadin · #7 06-18-2014, 09:56 PM

Quote:

Is that by weight or volume?

Ha! Weight times volume of course! (Inverse density!)

Simpler=Better · #8 06-19-2014, 07:34 AM

If you don't care about looks buy an appropriately sized air line drier from HF and fill it with steel wool.

dieselbenz1 · #9 06-19-2014, 08:00 AM

I ran several different types for 5 years and can't say I'm totally happy with any. The one you selected has benefits in that it is a sealed unit some tend to vibrate loose making a real mess and if it drips on the exhaust manifold could cause a fire. I would be Leary to put steel wool into oil which lubricates your fine engine without some type of filter before it reaches the sump. 5/8 inlet and outlet should be the minimum size vapor lines anything smaller may cause excess engine pressure build up causing leaks. Just a few things to consider.