Does blow-by cause smoke? - PeachParts Mercedes-Benz Forum

Ceristimo · #1 09-23-2015, 12:37 PM

Hey guys,

Betsie has some blow-by. I was under the impression she didn't have any blow-by, but I always checked with a cold engine.
I checked her a few weeks ago with a warm engine, and had to conclude that she does have blow-by; the oil cap dances somewhat and she smokes out of the oil filler hole.

My question is this:
Does blow-by cause the engine to smoke more? Lately I've been getting dark smoke out of the tailpipe when the engine is cold and idling, but I think a valve-adjustment would help with that. So I am not too worried about the dark smoke when she's cold.

However, yesterday as the engine was hot and I had the car idling in my garage (with the door open), I noticed a thin layer of smoke around the hood of the car (none out of the tailpipe).

So I popped the hood, and I can see thin whisps of dark smoking coming out of my air filter lid.
I pulled the breather tube on top of the air filter housing, and it's billowing smoke.

Is this caused by blow-by and should I not worry too much (after all, 280K is...well, quite a lot!

), or is it not normal for smoke to come out of the breather tube on higher-mileage engines with moderate blow-by?

The smoke is coming out of the top of the air filter housing because some previous owner mangled up the air filter lid a little, and it doesn't make a perfect seal.

The car starts effortlessly at 25f (-5c), and seems to have plenty power and runs fine - except very clackety when she's cold. I really am not worried about the blow-by at all, but I don't know if the smoke coming out of the breather tube is normal... I would assume it is, but still, thought I'd check with the more knowledgeable folks

.

leathermang · #2 09-23-2015, 12:48 PM

Set the valves since you know they need it.... take an aspirin .....and come back and tell us if things are better, the same, etc....

Ceristimo · #3 09-23-2015, 12:56 PM

Not sure why I would need an aspirin, I don't have a head-ache.

Yeah, I should do the valves. It's been about 10.000 miles since the last adjustment, but the last adjustment was done by the previous owner, and I don't know how well he did it.
He did give me the bend wrenches with the car to do the valve adjustment.
Thing is, I've been putting it off, because the Mercedes driving season will only be a few more weeks. We're gonna get snow and ice soon, and I won't drive Betsie in winter. Figure I'd do it in a few weeks.

You think the dark smoke out of the tail pipe when she's cold, and the smoke coming out of the breather tube when she's hot are related?

ah-kay · #4 09-23-2015, 01:03 PM

Smoke ( white, black ) can be caused by a lot of factors in an old diesel.

1) Incomplete combustion - worn rings, low compression, valve adjustments. Any or all of the above. Blow by is caused by worn rings.
2) Coolant breached
3) Turbo oil seal - this will be like a smoking machine.

How smoky is relative. You would expect some smoke or blow by in an old diesel. Just enjoy the car if cars behind you is not avoiding or steering away from you.

leathermang · #5 09-23-2015, 01:19 PM

Smoke... ' black , white' etc... is really hard to determine... if one has seen samples of illusions so many things influence what we ' see'... things like the color of what is behind the smoke you are looking at...the type and intensity of the light... etc...
Really Black smoke may be easy to identify... but anything less is subject to the conditions present....

Ceristimo · #6 09-23-2015, 01:27 PM

Just to make it clear:

I am NOT worried about the smoke out of the tailpipe when the engine is cold. The smoke is clearly visible, but disappears after a few minutes and is completely gone when the engine is warm. The smoke-on-cold out of the tailpipe will most likely get better after a valve adjustment.

My question was: Is it normal for an engine with blow-by to smoke out of the valve cover breather?
I would assume it is, as blow-by engine also smoke out of the oil filler cap, but I thought I'd check. The reason that prompted the question is because my car is visibly smoking out of the air filter housing, since the lid does not make a tight seal, and it looks a little funky to see smoke coming out of the hood...
This smoke is not visible when outside, but in my garage where there is no wind you can see some smoke coming out of the hood.

leathermang · #7 09-23-2015, 01:31 PM

When you do your valve setting... why don't you replace your valve stem seals ? That smoke upon start up ...but not when warm is often caused by worn valve stem seals....

Ceristimo · #8 09-23-2015, 02:01 PM

Well, that doesn't sound like a bad idea, actually, though it might be a bit too complicated for me.
Betsie doesn't really use much oil, I'd think that having worn valve stem seals would cause high oil usage?

leathermang · #9 09-23-2015, 02:57 PM

No, a gradual amount not necessarily detectable...as they do not fail all of a sudden... just get worn to where some oil leaks into the combustion chamber and is burned when you start up the engine the next time...
but at some point of really being worn... yes...increases your oil consumption.

ah-kay · #10 09-23-2015, 03:03 PM

Quote:

Originally Posted by ah-kay

Just enjoy the car if cars behind you is not avoiding or steering away from you.

This statement still stands.

If smoke comes out of the valve cover then the engine is worn and tired. However, if it starts in Alaska every morning then I would just keep driving it until it needs a complete overhaul. Changing the valve guides nor adjusting the valves would make no noticeable differences IMO.

leathermang · #11 09-23-2015, 03:31 PM

He has never set the valves on this car.... so I think he will sleep better through the long Alaskan night if he does that at the end of this driving season...

barry12345 · #12 09-23-2015, 05:51 PM

If the air filter is not oil saturated I would not be concerned. Other than get a new filter box cover off a wreck or somehow if it is distorted or does not fit well.

The fumes can make you sick on a decent run if they get into the passenger compartment. As for the base oil consumption. Getting less consumption than say 1500 a quart. The engine still has a lot of time left in it usually. Of course you cannot judge that if there are signifigant oil leaks.

Since blow by as the name implies is the combustion gasses getting past the piston rings. It will always contain some of the combustion gases containing burnt fuel smoke that enable it.

Ceristimo · #13 09-23-2015, 08:23 PM

Thanks for the responses guys.

I changed the air filter when I got the car, and it is not soaked in oil, though there is a little bit of oil there. It seems the oil separator in the air filter housing is not doing it's job fully anymore.
I also have a tiny bit of oil in the U-bend hose that goes to the turbo charger, which might mean I need to take a hard look at the turbo seals. I had that planned as a winter project, to rebuild the turbo. The turbo also audibly whines.

The car stars fine at 25f, but I've noticed I need to wait some 5 seconds after the glow plug light goes out before I start it. When it's freezing and I start right after the light goes out I need to crank for 2-3 seconds, whereas if I wait 5-10 seconds more she starts instantaneous. I generally use the seat belt light right next to the glow plug light as my glow light. When the seat belt light goes off I start her

I will definitely also set the valves, but since Betsie is not my daily driver and I don't drive her in the rain either, I don't put many miles on her. I think I've gone about 3000 miles since I bought her in February of this year, and I won't be adding many more this year.

The filter housing is indeed a bit mangled up on the top (the lid also makes an annoying rattling noise when the engine idles, and I can't get it tight enough to make it stop rattling), but since I can't find a W123 in a junk yard here I'll have to search Ebay for a replacement I guess.

Bottom line: I won't worry too much about the smoke. The car's old and the engine is starting to show it's age, and frankly that's OK with me: we're talking about a 31 year old vehicle that has been a daily driver all it's life, so it's OK if it's not in showroom condition. I don't expect her to be.

This winter it'll be time for new rear axles (the boots have been torn for thousands of miles at this point, but surprisingly the axles don't make any noise), and a valve adjustment and possible timing chain, although the timing chain replacement makes me nervous just thinking about it...

Thanks guys!

pgringo · #14 09-23-2015, 08:48 PM

do the valve adjustment. it's not that difficult and you *could* see a nice payoff in get up and go.

i drove the snot out of my 300sd that had blowby so bad a constant stream of black smoke would spew out the oil filler cap if you just unsealed it. almost zero smoke would come out the tailpipe. the oil in the blowby was so bad i had to make a custom air/oil separator that was more effective than stock. i drove that car like i stole it every day for 8 years, using the go pedal as an on/off switch.

edit: oh yeah...in freezing weather she would start in about one full second of crank after letting the glow plugs do their thing.

leathermang · #15 09-23-2015, 08:48 PM

The FSM says the glow plugs will continue to get hotter at least to forty five seconds.. there is a chart in the FSM....
so I suggest you let it heat for like twenty seconds and save the wear on the starter.
Turning the key on repeatedly is not what the FSM suggests.... just turn the key on and time it. Don't worry about when the light goes off...