Trying to learn about crankcase ventilation. - PeachParts Mercedes-Benz Forum

Ross Davis · #1 05-26-2009, 07:58 AM

Good morning.

I had some time to look around my engine compartment this weekend, trying to learn more about the design of these diesels. One of the things I did was to take the air filter housing off of the turbo, to learn more about the layout of those components.

My interpretation of what I saw is that the "oil handler" at the center of the air filter housing has a way to divert the oil component of crankcase gasses both down the oil drain tube that returns to the oil pan (as I understand at this point), but also back into the turbo. In other words, what is being sent into the turbo via the short black pipe that exits the "oil handler" at the center of the air filter housing.

The uneducated person (me) might think there was some "advantage" to increased "blow-by", as there is continuity between the crankcase and the tubo underneath the lid of the air filter housing; more "blow-by" just sends more air into the turbo via this device at the center of the filter housing.

Thanks for entertaining my questions.

Actros617 · #2 05-26-2009, 09:14 AM

Only oil goes through the oil return line (sometimes gases goes through the oil return pipe), and the vent gases goes through the short black pipe and sends back into the intake, on a diesel car the crankcase gases goes into the intake voluntarly meaning there is not form of vacuume helping it to suck the gas in. some one told me there is a slight benifit in letting the crankcase vent into the intake (please correct me if i am wrong)

scottmcphee · #3 05-26-2009, 02:05 PM

On my car, there is an oil separator built into the valve cover, takes the heavier droplets out of the crankcase gasses... gasses that come up from the bottom end (blow-by) up through the oil duct work in the head and chain cover. These gasses are routed via black plastic tube to the intake side of the turbo. No need to send gasses through the air filter again.. it's filtered air. Albeit oily filtered air. This is one reason why the air intake tubing and manifold gets oily inside. The other reason is EGR exhaust gas return, if you have that / still hooked up. EGR returns burned gasses into the mix again through air intake, and I think is a much worse contributor to gunked up intakes than PCV. Positive Crankcase Ventilation.. positive for a reason.. it's under pressure because blow-by is forceful. Doesn't matter that a diesel creates no meaningful level of vacuum in the intake... the crankcase gasses are being pushed, and the intake is sucking some serious air... it's all going back into the cylinders. If you prevent PCV from going down its tube, you risk blowing out a valve cover gasket or some other gasket/s so let it "breathe".

kerry · #4 05-26-2009, 02:12 PM

MB used different kinds of Positive Crankcase Ventilation systems. On the early turbo SD's the valve cover is vented directly into the turbo air intake pipe so any oil in the air is fed thru the turbo back into the intake manifold. A later design was the oil separator in the air filter. This allows the oil in the blowby to drain back into the oil pan and the smoky air gets sucked back into the turbo intake.
In your design, I believe no oil is fed back into the turbo thru the PCV system. The oil goes back to the pan and the air back into the intake.

moon161 · #5 05-26-2009, 02:33 PM

Some years of 240D have a butterfly between the air cleaner and intake manifold. This puts the manifold and crankcase under vacuum.

scottmcphee · #6 05-26-2009, 03:07 PM

Quote:

Originally Posted by moon161

Some years of 240D have a butterfly between the air cleaner and intake manifold. This puts the manifold and crankcase under vacuum.

Aahhhh! Putting the missing gasser "throttle" back in, to create vacuum.

I kinda wonder why this general approach is not commonly done to get rid of the vacuum pump on the diesel engine, you know, to supply vacuum for brakes and all the extra plumbing that runs on vacuum tubing?

Diesel911 · #7 05-26-2009, 03:52 PM

Quote:

Originally Posted by moon161

Some years of 240D have a butterfly between the air cleaner and intake manifold. This puts the manifold and crankcase under vacuum.

Those Engines with the Butterfly Valve in the Intake Manifold are also Engines where the Fuel Injection Pump has a Pneumatic Governor.
So the Vacuum is needed to operate the IP.

#8 05-26-2009, 03:54 PM

Quote:

Originally Posted by scottmcphee

I kinda wonder why this general approach is not commonly done to get rid of the vacuum pump on the diesel engine

A vacuum pump is far more efficient than a throttle.

#9 05-26-2009, 03:55 PM

Quote:

Originally Posted by Diesel911

Those Engines with the Butterfly Valve in the Intake Manifold are also Engines where the Fuel Injection Pump has a Pneumatic Governor.
So the Vacuum is needed to operate the IP.

Not on 81-83 240D models. Its used to force exhaust through the EGR.

mytmousemalibu · #10 05-26-2009, 04:38 PM

FI do you have any more info on the 240D vaccum/fuel system? Or links to some?

My buddie has an iirc 84 but might be older, that i need to get running for him. It has a throttle blade.

Ross Davis · #11 05-26-2009, 04:56 PM

Thanks for the replies.

Kerry, at my basic level of understanding, your explanation helps me the most. So that "device"/oil separator (that I was tempted to disassemble but did not) that rests in the center of the air filter housing has the ability to send "blow-by" oil back to the oil pan pathway, and "blow-by" air/gasses back into the turbo. I wonder how it separates the two; by the density of oil vs. air?

I read alot about "blow-by" (none, a little, a lot, indicates wear, doesn't matter, etc.). It almost seems like "the system" was designed to account for blow-by, separate its components (oil and air), and return them to appropriate places by separate pathways.

Thanks.