Engine vent smoking on mercedes 190d
 

Hi-

I have a 1984 190d 2.2 with 4 cylinder engine (non-turbo) that has a small hole in the cylinder head cover on the passenger side. According to the manual, this is to vent the diaphragm chamber in the pressure control valve (see pic below) It smokes a lot through that hole and when I'm idling, the smell gets blown into the car through the climate control air vents. Pretty smelly and nasty.

Does anyone know if I can
1. block this hole (on another 190d I looked at, the hole appeared to be hidden/blocked with a sticker); or
2. reduce the smell through the climate control vents by another means? I don't know where the climate control vent draws the air from, so perhaps I could make sure it's not drawing in the smoke.

Any ideas would be most appreciated. Thanks.

I like the smell at idle, it's the only time I get to appreciate the smell of the biodiesel I use. The rest of the time it's wasted on the ga$$er behind me
:lol:

I wanted to point out that the smell is burning motor oil and not diesel/biodiesel.

Does the motor smoke alot under the hood?

Not a huge amount, but there is a steady stream of smoke from the "vent"

The hole is there so the regulator in the valve cover knows what atmospheric pressure is. It needs to know that so it can properly do its job of regulating the suction from the turbo inlet that pulls vapor out of the crankcase. Smoke coming out suggests that there's something wrong -- with the regulator or something else.

Boooney, do two tests for us and report back:

(1) with the engine warm and idling, remove the oil filler cap. Do you get a huge cloud of smoke/vapor (blowby) from the valve cover?

(2) Put the cap back but don't tighten it. Does the cap dance around like the lid on a teakettle?

Jeremy

Jeremy,

I did these tests already. There is a fair amount of blowby and oil splatters outside of the oil filler when I remove the cap. The cap does rattle around a lot like the lid on the tea kettle.

By the way, this car isn't turbo, so does it need the hole for the turbo inlet that pulls vapor out of the crankcase?

Thanks.

Mercedes probably had a good reason for designing it with one.

The reason I'm asking is because I have seen another 190d without the hole and it works fine...

Shouldn't it be hooked up to an oil sep or a draft tube or something?

My 190d 2.5 turbo has the same hole and it's a very annoying one as when it spits oil outside.

Your relatively high level of blowby may mean that the pressure inside the valve cover is more than can be handled by the "PCV" system. The excess pressure is escaping any way it can, by going through the vent. Another possibility is that something is wrong with the vent system (hose collapsed or plugged up) and the blowby is escaping through the little vent. Better that than blowing a seal, I suppose.

Engines that don't have a vent in the side of the valve cover probably use a different type of oil breather. The vent hole is not hooked up to a tube because it's designed only to let the pressure regulator sense atmospheric pressure. In a new engine, the regulator keeps intake vacuum from pulling oil out of the crankcase. In an engine with very high blowby, all bets are off.

Jeremy,

This is great info. Thanks. I expect that there is extensive blow-by. As a last resort, how do I check for a clogged vent?

With the engine idling, pull the plastic vent hose out of the intake pipe and see if crankcase vapor is coming out of it. If you have as much blowby as you say, it should be spouting like The Little Engine That Could.

Vent Hose: Do you mean the black plastic hose on the top of the engine?