BMW M5 Forum and M6 Forums banner

Oil separators... buy new or clean by flushing...

2.5K views 19 replies 7 participants last post by  M5CS_Mpls  
#1 ·
My M5 has run without issue, engine wise (with 138K miles), since I bought it 10 years ago. But at 24 years of age, it's time for some maintenance items that need to be done even if they aren't broke... yet.

Some I'm doing all the "down in the valley" items (hoses, O-rings, the hollow L connector (plastic to brass), etc.).
The oil separator hoses are getting quite soft, so of course they will be replaced. However, I thought I had read a post from back when, that said the can be flushed out using carb fluid till it runs clear and reuse. I have spent the last hour searching the Board for that thread or any like it saying flushing works or any insights as to what if anything is inside the separator, with no luck.

So, this why the post. Spend $250 - $310 for a replacement kit (ALL the parts) or ~$100 - $150 for BMW hoses, flush the separators and reuse.

What say you??? Thanks in advance.
 
#2 ·
Long ago there were some things identified. They can get a tad rough inside but I doubt that is an issue. The main issue when we were looking at separating the oil was most of us had too much oil going through them. At the time no one really realized that any leaks in gaskets were allowing unmetered air into the engine but also that extra air was grabbing a ton of oil on it's path to the plenum. Once we started replacing gaskets and stopping the extra air, not only did the cars run better but there was less oil going to the separators and old roughed up ones could still do the job.
Moral of the story is if your separators don't seem to work it is likely they are seeing too much oil and a better choice would be to stop the source of too much oil. If doing maintenance I think it would be better to spend the money on new valve cover gaskets and that refreshment will prevent extra air so your old separators will still do their job.
 
#3 ·
At this point, there a lite misting coat of oil in the plenum and the horns, but no puddled oil. All the other pipes and hoses look very good... not brittle or creaking (much to my surprise). Valve covers have never leaked oil (shock, I know... have never had them off). Never have had the spark plugs out (of the 138K miles on it, only 23K are mine). Looking the spark plug valley, no oil, at all. As I say, this thing has been without issue engine wise... always starts instantly even after it's winter storage. I have been VERY lucky with it.
So all this is general PM. May have some potential vacuum leaks, will double check and verify.
 
#4 ·
That is the thing that we missed in the early days and why people were blaming the separator, car never leaks oil unless the leak is below the static oil level. The car runs a constant vacuum in the crank because of the direct connection of the crankcase and plenum. Valve covers don't often show signs of leaking because they are above the oil level and when running air is getting suck in the leak so oil can't get out. If you have a light mist of oil in the plenum you have air leaks somewhere. Not to say that is VC it is just somewhere, you have to figure that out but I would say the life expectancy of VCs is less than ten years.
 
#5 ·
Short direct answer is you can definitely clean them. There are no moving parts inside and the holes are pretty large. It takes a lot of sludge build up for it to be a "real" issue. Even then, technically you can still clean them, but it becomes a calculation of cleaning time and materials versus new. For your case, I definitely recommend a quick cleaning is all. I just spray brake cleaner through both directions. Wear rubber gloves, plug one end with your finger, spray some cleaner in the other and shake it around. Don't waste your time waiting for the fluid to come out clear. Just watch for it to lighten up a lot from dark brown to semi-clear brown. That's plenty clean enough.

Congrats on having a trouble free engine for so long! I agree with your sentiment that PM is due anyway, and as Sailor says, those VC gaskets only last for so long. I'd do the couple small vac lines (including the fuel pressure regulator line), brass elbow upgrade, all oil separator hoses (3 small ones in the front of the lower plenum, 2 from plenum to VC's), the VC gaskets, spark plugs (I change mine every 25-30k miles due to carbon) the plenum lid gasket and 4 orings there. Inspect the plenum to TB's big rubber boot for wear on the ribs that surround the TB's. This is the main sealing area and if worn, might not reseal very good. At 138k it's probably fine, but I'd check.

Good luck!
 
  • Like
Reactions: M5CS_Mpls
#9 ·
Hi, Kind of a progress note here... "down in the valley" has taken a LOT longer that expected what with my age, high summer heat and constant waiting for parts, it has eaten up most of the summer. All good , mostly, now except one item... will get to that...

Image


Got the "valley" all cleaned out and indeed a couple small vacuum hoses has pin holes in them from rubbing.

EVERY hose, O-ring and O-ring items replaced; new PS pulley (did not realize they are plastic!!); VANOS high pressure lines; TBs soaked and cleaned; new plugs; had valve covers powder coated and new gaskets & rubber grommets; injectors cleaned and "calibrated" (so they all flow the same) along with the 2 O-rings on each injector (~$20 for the 2... ouch); new motor mounts; new A/C condenser and dryer; new thermostat and gaskets; must be more I can't think of at the moment.

Image


All cleaned up now. Started it without coolant for a minute or so just to verify that it would... no problem.

Then the problem. Put the coolant in and the valley started to fill up with it. Found one coolant hose clamp not tightened (daaauh), but fixed that and sill is leaking in the valley. Best I can tell, the oil/coolant heat exchanged O-ring got damaged during install. It's a blind install so could not tell. Used Vaseline on the O-ring and bore of the receiver but still no good. Used a new O-ring (Gasket ring 11441406702).

Any tips and getting this installed without issue?? Hate having to take all that out again but no other option.

This all started with a need for a new master cylinder and the while I'm in here syndrome went nuts. So, new one of those ( the E65 MC upgrade) and booster.
 
#10 ·
Holy smokes man you went DEEP under that plenum removing all of that including the throttle bodies! Unfortunately it does sound like you snipped an O ring where the Thermostat and the 3 tubes connect. I did the same and the coolant was coming out of the seam in my transmission case as that's where it manifested. Had to yank the plenum off again (I was also concerned about a engine ticking noise as I had just done the timing chain guides) and then pull the thermostat and immediately saw the O-ring that was broken. It made a distinct "click" when it went in that was a bit more "Clicky" than the typical dull "snap" you get when the o ring properly engages. Funny thing was that as soon as I pushed it in and heard that click sound, I thought I might have snapped one but chose not to remove and re-check. ARGGGHHHHHHH

Use more vasoline and go in as slowly as possible and as evenly as possible, if you hear a "click" you may want to pull and re-check things. Have many spare O rings for this area on hand.
 
#11 ·
I hear a lot about people using vaseline, but I've had success using undiluted coolant as lube when replacing the o-rings on the pipes to the thermostat housing. I've only done the job once, so I can't say it works every time, but I know others have used coolant for lube also. Might be worth a try if vaseline isn't working for you.
 
#15 ·
Annnd, now here's more leaking!! This time it the O-ring on the Auxiliary Fan Switch in/on the lower radiator hose. New radiator hose, but same switch. Getting new O-rings. RealOEM does not list a separate part number for the O-ring only but ECS Tuning and Bimmerworld both do. BMW switch with new O-ring $48 (from ~$6 to ~$48 depending on brand), O-ring only, $0.98

Almost done.
 
#16 ·
You're getting there! I've been in the habit of always replacing those sensors with new o rings anytime I do a cooling system overhaul as I just don't want to worry about any one part that might be old.. plus then if you get it all from FCP you now have a lifetime cooling system and can go all in to refresh the entire thing whenever you so choose!
 
#18 ·
This what happens when hope springs eternal... and this whole thing has taken all summer and can't wait to run it.

FYI: ECS Tuning & Bimmerworld have the O-rings as a separate part number ( 13621743299 ) for about $1 each. But waiting 3 or 4 days for the parts to show up was to painfull, I went to Motorworks BMW here in Minneapolis to get one as they had stock... $11 each!! The pain just changes location... lol
 
#20 · (Edited)
FYI Update: Finally, all back together and looking as pretty as can be.... just ran it for the second time. First time was with all the vacuum hoses off, no plenum, no coolant, etc. just5 to confirm that it would run... it did... did not sound great.
Today, all buttoned up, coolant and everything... started right up, settled down to a nice idle and just purred. (I know, I'm as shocked as you!!) Let it run up to temp and no leaks anywhere... halleluiah.

Image


Now, clean up the brakes (surface rust from sitting all summer in the rain); almost done with putting the new front bumper together. Have test fitted it and it fits well. @DesertTech did a great job painting both the front and rear bumpers as well as being a great help in general!!