W201 Crankcase Ventilation
 

('92 190E/2.3)

I have some oil present on my engine around the valve cover gasket and around the crankcase ventilation lines. While investigating this, I found that if I remove the oil filler cap with the car at idle, oil "spatters" out of the filler hole. Shouldn't there be vacuum present that prevents this?

Further investigation revealed an electrical component that appears to be part of the crankcase ventilation system. It is positioned between the intake ports of cylinders 3 & 4.

So I have 3 questions:

1) How does the crankcase ventilation system work on this car?

2) Is mine working properly?

3) What is that electical component?

Thanks in advance for any insight you can offer.

Jeff Pierce

It's common on most cars to get some oil accumulation around the PCV lines, so removing them and flushing them out with mineral spirits periodically is a good idea along with cleaning up any oil film inside the air cleaner housing.

Not sure if your system is configured the same, but my '88 190E 2.6 has a circulation system that draws fresh air through air cleaner, circulates it through the crankcase where it picks up blowby and then into the inlet manifold through a restrictor.

During less than WOT operation, manifold vacuum keeps the air circulating "forward", but flow at high vacuum is limited by the restrictor. During WOT operation since there is little manifold vacuum, the flow can actually reverse, which is why a film of oil will buildup inside the air clearen housing.

Since a rocker arm is right under the oil fill cap, if you remove it while the engine is running it will fling oil. The "vacuum" in the crankcase due to the PCV system is, at most, an inch or two H2O, and upon loosening the oil fill cap, the very small crankcase vacuum immediately bleeds down to zero.

Don't know about the electrical component you refer to, but I doubt if it's part of the PCV system. The are several sensors and switches mounted along the inlet side of the head, next to the cam cover.

Duke

Based on the location you describe, the component you refer to is the rotary idle control valve. It controls the idle speed by the current from the ECU. Air is drawn through it from the rubber plenum connecting the airflow meter to the throttle body, and thence into the intake at the idle air distributor port. There is a 'Y' in the plumbing at this point where the hose runs parallel to the valve cover, branching into the breather hose connecting the valve cover to the air cleaner. At this junction is the pcv device. From the outside it just appears to be a plastic hose connector with an additional small port going to the back of the fuel pressure regulator. If fact, it has a flow restricting orifice, and the third port connects to the 'breather' side. Almost nothing can fail with this device.

Steve

Duke,

Thanks for the info. Frankly, I wasn't sure which way the system flowed. With your explanation, it makes sense to me now. BTW, thanks for your response a couple of days ago to my coolant leak problem. It was a heater hose leak. I just couldn't see it because it was located on the bottom side of the hose.


Steve,

That's it -- the idle control valve. Thanks for your detailed explanation.


Jeff Pierce