Oil in Intake/AirBox

[purple haze]

Hey all,
Was just servicing my 89 320i today, when i took apart the air box to change the filter i came accross an oil saturated filter and a pool of oil in the bottom of the box, I took of the AFM and found more oil.



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What should i start with?

[purple haze]

I'l add that i had a compression test done last year and came back fine.

[jlevie]

That isn't abnormal on a higher mileage M20 engine. Wear of the rings or cylinders increases blow by and thus the flow of oil vapor into the intake. Other than make a mess that doesn't really hurt anything until the blow get's really bad and the car starts producing a smoke screen.

A leak down test tells more about the condition of the engine than a compression test.

[nando]

check the seals on the "tube of death" under the intake manifold

an oil film may me normal, but puddles is not.

for some odd reason, a big vac leak from that tube will cause oil to pool up in the intake.

[purple haze]

The Air filter was completely saturated in oil so its not something i can overlook as i doubt the car can breath properly.

Il have a look at the "tube of death". should spray test the seal with aero start?

im at about 198xxx on the odo so its pretty high mileage.

[nando]

no it doesn't connect to the intake. I don't fully understand how it can cause oil to back up into the intake manifold, but it definitely did - when I first built my motor in 2006 it sucked almost a full quart all the way to the airbox. I thought I screwed up the build, but then I found out the tube of death wasn't sealed right. Got that fixed and it went away.. that was 80,000 miles ago.

The o-rings will need replaced, there's one at the top and one at the bottom. probably worth redoing all the intake manifold gaskets while you're at it, and possibly having the injectors rebuilt/serviced.

[Northern]

Possibly coming from pcv? Both my m20s have a small amount of oil in the tb that I assume is from this.

[jlevie]

no it doesn't connect to the intake. I don't fully understand how it can cause oil to back up into the intake manifold, but it definitely did - when I first built my motor in 2006 it sucked almost a full quart all the way to the airbox. I thought I screwed up the build, but then I found out the tube of death wasn't sealed right. Got that fixed and it went away.. that was 80,000 miles ago.

That is easy to explain. The crankcase is at less than atmospheric pressure (the intake sucks on it). An air leak at the oil return tube, or anywhere else on the block, increases the airflow from the block into the intake. Which drags more oil vapor into the intake. There are several places other than the oil return tube to have leaks and a smoke test is the way to find them.

[Quinthirty]

check the seals on the "tube of death" under the intake manifold

an oil film may me normal, but puddles is not.

for some odd reason, a big vac leak from that tube will cause oil to pool up in the intake.

Does that mean that oil film up to the black elbow boot is normal?

[nando]

a little oil film is normal, puddles and a soaked filter aren't.

[jlevie]

a little oil film is normal, puddles and a soaked filter aren't.

Correct!

[jeffnhiscars]

It wont fix the cause but if you drill a small drain hole in the TPS cover it should limit the symptoms until you find the problem.

[purple haze]

I have stared pulling off the intake today, and have a few Questions.

1. noticed the the metal L pipe connecter the goes from the throttle body to the Idle control Valve tube was pretty loose and easy to get off,
do i need a new Part when i re-install there seems be be no seals for these connectors or is that normal?

2. Once i have resealed the Oil Return Tube will this eliminate vacuum seal as the problem of oil in the airbox or what other things should i check while i have the manifold off?

3. Bit of a noob question but do i really need to replace the hose clamps that i have loosened?

[jlevie]

The metal elbows on the sides of the throttle body were pressed in. Over time they will loosen and be the cause of an intake leak. The fix is easy. Clean the nipple and bore with acetone or lacquer thinner and glue the elbow in with JBweld. Do this with everything assembled so the elbow is at the correct angle. Allow the epoxy to cure for 24 hours before running the engine.

New o-rings will fix any intake leaks at the oil return tube, but there are other possible leaks. Replace the valve cover gasket and the four rubber rocker shaft plugs, the oil filler cap, and the dip stick o-rings. When everything is back together, have a smoke test done.

Unless damaged, screw type hose clamps can be reused.

[dnguyen1963]

I have stared pulling off the intake today, and have a few Questions.

3. Bit of a noob question but do i really need to replace the hose clamps that i have loosened?

If it is BMW crimp-style clamp then the answer is no.