Has anyone tried to block the vent hose from the valve cover? Tried this on a few 300TD's and the engine just stalls. I just pull off the hose and put my thumb over the venthole. Don't know why this happens... All of the cars had high mileage, and low compression.

Hi Bkr.

It is supposed to do that.
The only problem is that if the
engine shuts off immediatly the
engine has very low compression
and will most likely need rebuilding.

If the engine shuts off after 10+sec
you have a healthy engine.

Louis.

i just tried plugging my valve cover breather hose, and my engine never stalled out after 5 minutes, but when i let go, i got sprayed with oily exhaust!

is this good or bad?

__________________
1991 300 D 2.5 Turbo, 220k
also in the family:
1981 240 D 185k
1991 350 SD 185k
2006 S 500
2005 SLK 350

Grdenko.

Yes,that is good this means that you have good
compression.
Just your face doesn't like it.

I have heard of engines running for 20 min.
before shutting off.

Louis.

Plugging the hose increases pressure in the crankcase, which is functionally the equivalent of pulling a vacuum on your shut off valve. Hence, it shuts down.
Failing to shut down could be as simple as a problem with the shut off valve diaphragm or a bad gasket somewhere. Plugging the vent will have a tendency to blow seals as crankcase pressure increases.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

yeah, thats why i let go after only a couple minutes. i was afraid i was going to hear a POP! and then a hiss of some kind if i kept holding the vent closed.

__________________
1991 300 D 2.5 Turbo, 220k
also in the family:
1981 240 D 185k
1991 350 SD 185k
2006 S 500
2005 SLK 350

My '81 240d shuts down after 3 seconds with breather blocked, yet it starts instantly in the coldest of weather(no block heater). So where's the compression problem there? I also have high oil pressure, needle pegs at start up and never goes down except in the hottest days in August with the ac on. Any realtionship between blowby and high oil pressure?

yes, high blowby would increase the oil pressure. when i plugged the vent hose on my valve cover, oil started running out of the top of the dipstick tube.

__________________
1991 300 D 2.5 Turbo, 220k
also in the family:
1981 240 D 185k
1991 350 SD 185k
2006 S 500
2005 SLK 350

This answers the question from the post about high oil consumption when the breather tube was crimped.
The check valve in the separator return line must have failed and the pressure in the crankcase combined with the vacuum in the intake sucked the oil into the combustion chambers.

It does leave the question as to why the engine did not shut off if the breather was crimped. Could it be that enough oil was escaping via the return tube that the pressure never got high enough to activate the shut-off?

Anyone ever check the check valve in their engine?

Is this an argument for a pressure relief valve on our engines like is found on hot water heaters?

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Punky -

You probably don't have high oil pressure (unless you have checked it with a manual gauge and know its high). Your oil pressure should be pegged while you are driving. That highest mark is only about 45 psi.

As to the engine shutting down quickly when blocking the breather, while it still starts and runs fine - ignore this thread and just keep driving it.....

my $.02,
Wes

Thanks for the info. When I said oil gauge pegs, what I meant is that at any idle speed, low or high, hot or cold it's pegged until I turn the car off. I won't worry about it, it's just one more odd thing about this car.

You could stick a crow bar in the oil fill hole into the valve train if the crow bar breaks before the cam then the cam is good...........

William Rogers..........

Can we try that technique on your car first?

Howdy,

I was wondering if this technique could damage the engine? I have heard that running excessive crankcase pressure can blow oil seals out of the engine.

Sholin

__________________
What else, '73 MB 280 SEL (Lt Blue)
Daily driver: '84 190D 2.2 5 spd.