[Schantin]

This is a follow-up post to a question I originally had regarding oil noted in my intake pipe after installing a Dinan CAI.

The short version is that the BMW B46 4-cylinder engine positive crankcase ventilation (PCV) tube sprays oil vapor into the intake tract just before the turbo compressor inlet. I know this from doing research on the topic and by physically inspecting my PCV and stock / Dinan air intake tubes.

Now, you would probably wonder WHY this happens on a new factory stock vehicle. In regards to BMW, it's a product of boost. Boost pressure increases crankcase pressure, which leads to more oil in the intake. Theoretically, the piston rings should be perfect and seal the combustion chamber. However, the reality is that there is a percentage of air that gets past them, even in a new car. Boosted engines exacerbate this. This air + accompanying oil vapor is sucked from the crankcase back to the intake via the positive crankcase ventilation (PCV) valve. Adding to this is that the PCV in a B46 BMW enters the intake air stream just prior to the turbo compressor, which is creating a tremendous vacuum from spinning to ingest air and create boost pressure. Venting these gasses to atmosphere is considered an emissions faux-pas, so they are recirculated to allow the engine to "burn them off." However, in the B46 (B48), oil residue collects in the turbine compressor inlet. I pulled my PCV and the entire tube was damp with oil residue. The stock intake I pulled from the car was slicked with a thin film of oil after only 10k miles. The Dinan intake was similar after 2k miles. The fact there is an oil seal between the intake tube and turbine inlet is a fair indicator BMW knows this. The issue is already a known fact in the 335i and some other older BMWs.

I decided that I don't want oil getting sucked into my intake and took matters into my own hands to rectify the situation. This is my personal $0.02 to fix an issue I feel exists and I provide this info to accept or reject as you see fit. That said, I added an oil catch can. And, yes, so far it works fabulously.

The catch can I used was a semi-cheapo system I bought from AutoZone made by Dorman. Normally I'd just use the word "cheap", but this is actually a solid piece of kit in general. It was also $100, so I'm not surprised it's made of billet aluminum.


Assembly is very straight forward. I cut the stock PCV tubing with an X-acto knife just after the bend where it exists the engine cover. The tubing provided in the Dorman kit neatly slides into the BMW tubing like it was meant to go there. I secured it with 2x hose clamps. As for the actual catch can, I attached it to the Dinan CAI box with 2x bolts.






So, since installing it I've driven the car 25 miles over a couple days. Lots of start / stop driving. Done a few full drag launches on it. Gone full throttle to idle to full throttle again several times. Brought it up to 100mph a couple days in a row, followed by long stints at idle. In short, I was borderline abusive to see what might happen. The verdict is no engine CELS, no adverse driving issues, and most importantly....... no oil whatsoever in the intake track. I disassembled the catch can. It reeked of oil residue and vapor. In short, it's doing it's job. In addition, I swear the car feels noticeably faster. It shouldn't as this isn't a performance mod. Maybe my car is enjoying breathing non-oil smudged air for a change. ......

[Soul_Glo]

This is a must for our cars. I have installed one on every BMW, I have ever owned. the 435d used to get half full after 8-10 months. Definitely worth considering whether diesel or not.

[peelerec]

Back in my Evo days this was a known issue as well. However most oil catch cans tend to stink up pretty bad within the week. Any odor coming into the cabin?

Would you recommend this for the B58 as well? I personally have not read anything on the forums regarding an issue in my 1-2 years on this forum.

[Schantin]

Originally Posted by peelerec

Back in my Evo days this was a known issue as well. However most oil catch cans tend to stink up pretty bad within the week. Any odor coming into the cabin?

Would you recommend this for the B58 as well? I personally have not read anything on the forums regarding an issue in my 1-2 years on this forum.

I'm not getting any smell from the catch can.

I haven't looked at the 6-cylinder BMW engine, so I can't answer your Q. I just know what I've observed in the 4-cylinder model.

[gorthol]

AFAIK the B46/B48 cars already have an oil separator in the PCV system that recirculates oil back to the crankcase.

[Schantin]

Originally Posted by gorthol

AFAIK the B46/B48 cars already have an oil separator in the PCV system that recirculates oil back to the crankcase.

It might, but there's quite a bit of oil getting past this separator if this is true.

After driving 400 miles since installing the catch can, I looked to see what was in there. I emptied about 2 Tablespoons (around 30ml) of diluted "milkshake" oil and water from the can. I'm happy that stuff was in the can and not sprayed onto my turbine compressor inlet.

A small volume of oil vapor still gets past the catch can and to the intake, but it is significantly less than prior to install.

[Schantin]

Emptied my catch can again after another 500 miles. This is what was in it: about 1/4 cup of oil/water mix from the PCV. Looks like chocolate milk. Smells like exhaust infused oil.

[rmedina]

Originally Posted by Schantin

Emptied my catch can again after another 500 miles. This is what was in it: about 1/4 cup of oil/water mix from the PCV. Looks like chocolate milk. Smells like exhaust infused oil.

No comment on the pic.. lol

But yes, a catch can is must. I had one in both my 300C, Charger SRT, and my vette. Once I get my ride this will be first "mod" I do.

[F32Fleet]

Originally Posted by Schantin

This is a follow-up post to a question I originally had regarding oil noted in my intake pipe after installing a Dinan CAI.

The short version is that the BMW B46 4-cylinder engine positive crankcase ventilation (PCV) tube sprays oil vapor into the intake tract just before the turbo compressor inlet. I know this from doing research on the topic and by physically inspecting my PCV and stock / Dinan air intake tubes.

Now, you would probably wonder WHY this happens on a new factory stock vehicle. In regards to BMW, it's a product of boost. Boost pressure increases crankcase pressure, which leads to more oil in the intake. Theoretically, the piston rings should be perfect and seal the combustion chamber. However, the reality is that there is a percentage of air that gets past them, even in a new car. Boosted engines exacerbate this. This air + accompanying oil vapor is sucked from the crankcase back to the intake via the positive crankcase ventilation (PCV) valve. Adding to this is that the PCV in a B46 BMW enters the intake air stream just prior to the turbo compressor, which is creating a tremendous vacuum from spinning to ingest air and create boost pressure. Venting these gasses to atmosphere is considered an emissions faux-pas, so they are recirculated to allow the engine to "burn them off." However, in the B46 (B48), oil residue collects in the turbine compressor inlet. I pulled my PCV and the entire tube was damp with oil residue. The stock intake I pulled from the car was slicked with a thin film of oil after only 10k miles. The Dinan intake was [...]

BMW fixed the intake deposit problem back in 2010 with the N55.

Catch cans are solutions searching for problems.

[Schantin]

Originally Posted by F32Fleet

BMW fixed the intake deposit problem back in 2010 with the N55.

Catch cans are solutions searching for problems.

Nowhere in my post have I made discussion of oil deposits accumulating on the intake valves (which is an unwanted by-product from direct injection.)

What I have clearly demonstrated in pictures and research is that the catch can is preventing oil and water vapor from being sprayed into the turbine inlet.

[shuencl]

I just installed a CAI on my 230i and noticed a pool of oil in the same place. I only have 15K on my car and it is a 2021, it does look like it is excessive. Also in the last part of the intake tube right before the turbo the tube has what looks like sound baffling and it has oil pooling up in it as well.