My original OCC install consisted of the catch can connected to the line feeding the turbo inlet, nothing else. This means the hose from the valve cover to the intake manifold is still in use. After several months of driving with the OCC, there was still no oil showing on the OCC dipstick. After seeing several online posts with pics of their catch, I did some research.

According to the Bentley manual, the line to the turbo is used when manifold pressure is “under load”. The line to the intake manifold is used during “deceleration or idle”. Since most of my driving is not under load (I use a lot of cruise control and highway driving), the OCC wasn’t getting used. So, the question is, should I cap the manifold line, or route it to an OCC? Because of cost and ease of installation, I took the cap option. Bought two vent caps from my local Audi dealer, part number 036131510, removed the hose, and installed them. Peugeot also sells them as #0361.S4, and ECS Tuning sells them online, all for about $10 each. Didn’t take long to catch oil in the OCC. Hard part is figuring out how to remove the hose without breaking it. Once you see how the vent cap is designed, it’s pretty easy to figure out.

After a couple tanks of gas, I noticed crankcase oil level was down a quart. This is the first time this has happened - this engine hasn’t burned oil in the 20K miles / 2 years I’ve driven it. First guess is crankcase pressure is forcing oil past the valve stems into the combustion chamber. This implies the vent plugs I just installed messed things up. So, I ordered a Dual Boost Tap, bought some hose and a “tee” fitting, and connected the rear (passenger side) valve cover outlet to the existing OCC. While in there, I disconnected the turbo air inlet hose for a quick look. Worst fears realized --- oil puddle in the air chamber!

Made a couple calls about turbo repair / replacement. One shop that knows Garrett turbos, told me that high crankcase pressure can cause oil to “backflow” thru the turbo oil drain line, and cause the symptoms I’m seeing. Resolve the high crankcase pressure issue, and the oil consumption problem will go away. Then there’s an oily mess to clean up --- from the turbo air outlet to the intake manifold. This is several months after the initial OCC install. I’ve created the very mess the OCC was installed to prevent! The WMI system should keep the rest of the lines clean, once the oil source is removed.

After reading some of the various threads on OCC’s, oil consumption, and bad smells, it’s my guess that they have a similar problem --- 2 vent caps installed, or a dual boost tap adapter connected with the plug installed. I still don’t understand how this adapter can read boost when it’s connected to the crankcase / valve cover vent line. Maybe if installed at the manifold end of the hose and then plugged, but I don’t know what’s happening inside the throttle control box.

Anyhow, I installed a BSH Dual Boost Port Adapter on the valve cover, in place of the hose --- plugged the boost port connections, but not the main vent. Then routed a hose from this adapter to a “tee” I added to the OCC inlet hose. I’m trusting the Bentley manual when it indicates that only one of the two vents are active at any time.

After a lot of oil cleanup, a month or so of driving, and a couple tanks of gas, there seems to be no more oil consumption or leakage thru the turbo. It’s pretty easy to remove my turbo inlet hose to check it.

There are those who say I’m “all wet” with this theory, ‘cause they’ve had virtually no problem with their OCC single line install. It’s my belief that it’s all dependent on driving habits --- with the rear “low pressure” vent plugged, there is little or no pressure relief in the crankcase, so it builds up until it finds a path out --- in my case, the turbo seal. I’ve read where others have leaking valve cover gaskets --- another probable pressure relief path. My valve cover has been removed / replaced a couple times, so not a weak spot. The “burning oil” smell often noticed, in my case was probably from the oil puddle in the turbo air inlet chamber. When the engine is off, fumes can escape thru the air filter. There was also oil residue on the turbo outer surface, and the oil hoses aren’t leaking.

So, the reason for this post is to offer a solution to those of you with similar “sudden oil consumption” after an OCC install.

Here's an embarrassing update --- the dual OCC was NOT a fix! Turns out that my PCV was shot, preventing crankcase pressure from escaping to the turbo inlet. Changing the valve cover seems to have fixed it ('course, that's what I said about the dual OCC), but since I seldom "get on it", it's still up in the air.

 

Oil back feeding is a common problem for engines that do not have adequate venting to match the air flow its seeing. Mazdaspeed 3's do this stock for example since they were designed bad from the factory. Its a general rule that you never want to restrict a PCV system any more then it already is from the factory. Typically they are designed to barely handle the crank case pressure at their intended air flow. This is why most boosted cars that get re-tuned for increased boost levels will usually eat oil until the PCV system is re-done.

The most ideal route I've dealt with would be to just let the engine vent into a breather can rather then a catch can. You can generally find enough ways to vent the crank case beyond the needs of the engine and it wont drink oil. This will help keep things clean, reduce oil consumption and reduce the chance of knock.

Some engine set ups run better with a little vacuum on the PCV lines. this is a partial reason we see lines routed to the intake manifold and not just the port side intake pipe. Because of this a fully vented PVC can cause issues. It is possible to draw vacuum though from the exhaust system if set up right. This will allow for the breather to see some vacuum while not recirculating to the intake system. This has a added benefit of removing the breather filter in the engine bay and forcing any smell there may be out the exhaust.

From a personal stand point I had the best results on my car from running both the PCV and breather vented to atmosphere with the intake manifold and intake pipe ports blocked off. That's with a stock MCS turbo and 19 PSI boost. Since I was just testing things I didn't use a proper breather tank and just let a line from my catch can vent. From past experiences on other cars i was expecting a mess under the hood, but even after a few thousand miles it was not spitting oil out. I wouldn't recommend letting either side dump out like that, but it did show for that air flow and pressure level that it wasn't forcing much oil out.

 

Thanks for the input Mike. This is a much better explanation of the how / why I was getting serious oil consumption. It's always nice to have an experienced mechanic support my actions.

 

Interesting information. Do you have any pics of your final setup?

 

I was a bit premature in posting my "tee" fix. It slowed the oil use way down, but still burned oil. Probably as Mike says above, a vacuum is needed, and the turbo air inlet doesn't provide one. Another possible factor --- my motoring area is located at about 4500 ft elevation, and air pressure is noticeably lower --- my external manifold pressure gauge shows about 5mmHg with ignition on and engine off. At sea level, it shows zero, and at 9000' it shows about 10mmHg (switch on and engine off). Another factor --- compression tests show around 100PSI --- probably bad rings. Haven't tried a new gauge yet, but I don't think this is the cause of my oil use --- oil use started right after capping the rear PCV outlet.

In the interest of controlling emissions, I'm trying out a dual OCC. After a couple more months of driving, I'll check oil use again and post results.

Pics of the dual OCC installation are in my "garage".

 

Here's the promised update ---

After 3 - 4 tanks of gas, the oil consumption seems to have stopped --- at least, it's back to what it was before the original OCC install.

My turbo air inlet chamber is staying dry so any oil usage is probably due to the low compression readings. I was also noticing engine oil leaking from the engine / transmission "relief hole" (before the dual OCC install). That leak isn't there any more --- another indication that crankcase pressure is now closer to normal.

According to friends following me on mini club outings, exhaust smoke is now at a minimum --- no more "diesel smells".

I've made a couple waves with my opinions on OCC's, and probably PO'd a few people by bad-mouthing the single OCC / vent cap install. Those who say it works for them --- enjoy it! Those who have issues with oil consumption after a single OCC install, try a 2nd OCC, or a dual. It seems to have worked for me!

 

Is there anything wrong with using a single OCC on the driver side and leaving the hose connected on the passenger side? I had mine plugged for a while and also notice more oil usage. But I also had lower gas mileage. I put back the hose and the oil level stays ok and gas mileage is back up again.

 

First, a disclaimer --- I'm not a mechanic, nor do I have experience on any other Mini's besides my own.

Second, a short response --- a few of the other people that posted on this and other OCC threads have left the hose connected with no bad side effects. I have lots of respect for some of these people.

Third, my own opinion --- the OCC is installed to keep oil out of the intake manifold. Leaving one hose connected defeats the purpose of the OCC. I suggest you read the Bentley Manual section on emission controls, to learn how the two ports interact, then decide how you want to route this hose. Your driving style / habits should be the deciding factor.