'72 M117 engine - what is this line?

[Graham]

This question may have been lost in another thread:

I noticed one short hose connector under the hood of my 350SL 4.5L was wet with oil or something so changed it, but don't know what the line is.

It is a black hard plastic tube that connects down low on front passenger side of engine somewhere. It runs across the front of the engine and runs between power steering pump and valve cover on driver's side, then turns down and connects via a short piece of hose to a steel line that disappears down under the car. Any idea what this is?

[Graham]

Originally Posted by Gurunutkins

the pipe sounds very like the air injection pipe (difficult to say without a pic) but the air pump is low on the passenger side (about where the ac sits on the drivers side) and a pipe runs up to the botton of the passengerr manifold and another (plastic) across the engine to the drivers side where it connects to a metal pipe that goes back under the manifold to supply the driver side manifold. I removed mine so cannot send a pic of mine

let me know if that sounds about right
cheers
barri

barri - I don't think my '72 has air injection.

But your comment led me to look in the emission control section of the manual!

After reading the relevant part of section 14, I am pretty sure now that the line is a crankcase vent that connects to the fuel tank vent valve.

[wolf_walker]

Originally Posted by Graham

barri - I don't think my '72 has air injection.

But your comment led me to look in the emission control section of the manual!

After reading the relevant part of section 14, I am pretty sure now that the line is a crankcase vent that connects to the fuel tank vent valve.

My 73 M110 has that too, runs back to the two valves for the tank venting setup, which I don't quite understand, but it looks much the same.

[Graham]

Originally Posted by wolf_walker

My 73 M110 has that too, runs back to the two valves for the tank venting setup, which I don't quite understand, but it looks much the same.

Wolf,

The manual says that there are actually three valves. One opens on slight overpressure and feeds fumes to crankcase. Another opens on vacuum and lets air in. Another is a relief valve that opens if pressure is too high and this vents to atmosphere.

On the '72, this is apparently an all in one device and it is mounted in trunk area alongside expansion tank. On the '73, the valve assembly is under the car and it is of a different design.

At least learned something from fixing the "wet" connector!

[mercmad6.3]

It's the 'exhaust' for the charcoal canister. It just sucks air/fumes from the canister which in turn vents the fuel tank and prevents gasoline fumes from polluting the atmosphere. It should be connected to the intake on the engine on one end and the canister on the other.

[Graham]

Originally Posted by mercmad6.3

It's the 'exhaust' for the charcoal canister. It just sucks air/fumes from the canister which in turn vents the fuel tank and prevents gasoline fumes from polluting the atmosphere. It should be connected to the intake on the engine on one end and the canister on the other.

Merc - The charcoal canisters apparently only started in 1974. On these old cars, they just vented back to the crankcase which in turn vents into the intake.

Amazing what can be learned by reading the manual

[mercmad6.3]

Regardless of what the haynes book says,follow the line back and you will reach the canister and/ or vent cansiter. mercedes had the same thing fitted to US only delivered 6.3's in 1970.

[Graham]

Originally Posted by mercmad6.3

Regardless of what the haynes book says,follow the line back and you will reach the canister and/ or vent cansiter. mercedes had the same thing fitted to US only delivered 6.3's in 1970.

Merc - I don't have the Haynes book, but the MB shop manual describes a number of different vent systems for M117 engines starting from 1971. This is all in section 14.

The first mention of a charcoal filter is for the 1974 California version. '71,'72,'73 and '74 (Fed) all show a canister. I have no idea what is inside the canister, but no mention in documentation of charcoal filter until '74 CA model.

I have attached a picture of a 72/73 style SL canister as fitted in front of the trunk liner as well as the diagrams of the emission systems for the 72/73 M117 as well as the 74 California models. These show that the connection goes to the crankcase on the early models, but to the intake on the ones fitted with a charcoal filter.

Hope this helps someone down the road who has the same question!

[mercmad6.3]

well at least we all know now. On all mercedes that black line signifys the fume connnection regardless of where it is connected to the tank. Most post 1980 petrol mercs have it although I have two Asian delivered(W126 and W123's) cars in the moment which have neither the line or any canister,just the tank venting to a point under the car,just like a ponton.
I also have a 1976 W116 6.9 being stored here which has the same set up being a UK delivered car. In OZ,it wasn't until 1984 that the majority of mercedes delivered here got the canister and mainly it was because the W126's are like a right hand drive california car with regard to the emmisions fittings.