This is what a 617 looks like with NO blow-by (video) - Page 2 - PeachParts Mercedes-Benz Forum

miner · #16 07-15-2006, 01:16 AM

Quote:

Originally Posted by Diesel Giant

PCV system is on a gas engine using the naturally occuring vacuum to keep blow-by out of the crankcase. Not so on a diesel. The 617 is a blow-by monster yet the 603 rarely is seen with a lot of blow-by.

Earlier gas cars used what is called a road draft tube to vent the crankcase gasses out, but the EPA stopped that in 1965.

Doing the finger over the tube test would do nothing since nothing is coming out. Only works to give a mild indication of the severity of the blow-by.

Scientifically I am sure all cars including this one has some blow-by, but it is so minimal you can't see it.

I just thought others would like to see what these engines use to be like.....

I don't mean to be argumentative

. I just want to understand better. There seem to be lots of threads on blowby, but no real conclusion, just kind of conventional wisdom.

I know I saw PCV somewhere for these cars. Maybe it was in the Haynes manual. In the FSM they just call it "crankcase ventilation". Blowby gasses/oil vapors are created under the pistons and directed upwards where the oil is usually reclaimed and the gasses are fed into the air intake or vented to the outside.

The 617 has an oil seperator in the aircleaner that feeds back into the oil pan via a tube. At the end of the tube is a check valve that keeps oil vapors from getting sucked out of the pan by the air intake. (I don't know if blowby gasses can get into the lower oil pan. I wouldn't think so, normally, but if so then it is possible that people with very low blowby have a broken check valve so that all their blowby gasses are escaping into the air intake via this drain tube.)

The 603 has the oil seperator inside the valve cover and it also has a pressure regulator valve that vents the blowby to the outside via a little hole in the valve cover if the blowby pressure is too high.

Given this, I would expect to SEE more blowby in a 617 since none of the oil has been reclaimed as it exits through the vent tube. On the 603 I would expect to see less since the vapor goes through the oil seperator before being vented AND the pressure regulator controls the amount of blowby gas that is vented into the air intake. Neither engine neccessarily has more or less blowby in terms of positive gas pressure from the crankcase that needs to be vented, though. One may just be more visible than the other.

That's why I asked if you did the other tests. Your vapor could be miraculously free of oil (as I wish mine were so my aircleaner wasn't so oily

). In this case, you wouldn't see it as much, but it still could be there. Have you tried plugging the vent hole? And did it run a very long time? If so, then I would say that truly IS no blowby. But what does that mean for an engine that was designed with blowby/PCV in mind? I don't really know. You said your CD has more blowby but better performance.

It just seems like, if these engines were designed to ventilate the crankcase pressure via the vent hose, and you are not seeing this, then either your engine is producing no crankcase pressure or it is being vented somewhere else.

Please take this for what it is worth, though, as it has come from a noob. I could just be trying to justify my "moderate" blowby.

KylePavao · #17 07-15-2006, 01:21 AM

You got me depressed DG! Mine has some smokiness coming out, don't know if its bad or not..the engines starts without a heater always, and doesn't really burn a noticeable amount of oil.

Weird, now you got me all scared

pawoSD · #18 07-15-2006, 02:50 AM

Quote:

Originally Posted by KylePavao

You got me depressed DG! Mine has some smokiness coming out, don't know if its bad or not..the engines starts without a heater always, and doesn't really burn a noticeable amount of oil.

Weird, now you got me all scared

Your engine is perfectly healthy then, no being depressed!

Maroon 300D · #19 07-15-2006, 03:33 AM

Quote:

Originally Posted by KylePavao

You got me depressed DG! Mine has some smokiness coming out, don't know if its bad or not..the engines starts without a heater always, and doesn't really burn a noticeable amount of oil.

Weird, now you got me all scared

I'm sure your engine is fine, a little blowby doesn't seem to be an issue at all. Worst case scenario: it runs for only another 100K...

Actually I don't know enough about engines to say that, really, but I've read accounts here from several people who claim their cars have run for tens of thousands of miles at least in spite of fairly copious blowby. Just like pawoSD said about his car.

DG, please keep us updated on your drag racing project. In fact, if you ever posted a video of an old diesel Benz spanking a ricer, I'm sure it would be quite popular. Probably not with the guy in the Honda, though.

My car doesn't have any visible blowby, either. If I put some saran wrap over the filler hole it actually sucks in a little. If I just leave the cap off with the engine idling a little bit of oil does shoot out the hole, leaving small droplets on the valve cover. I didn't realize it before I read this thread but I guess that means I do have a little blowby. The engine moves quite a it, too, though, so I don't know...

My engine was rebuilt 116K ago.

DieselAddict · #20 07-15-2006, 03:41 AM

Diesel Giant, did you do this test with the engine cold? According to my observation, whether any vapor comes out of the oil fill hole depends on the engine temperature, type of oil used and outside weather condition. With a hot engine you'll get some vapor coming out even with the engine off. Whether droplets of oil are thrown out will also greatly depend on the engine temperature. IMO a better way to evaluate blowby is to just loosen the oil cap, eliminate engine vibration as a factor by changing the engine speed, and look for any motion of the cap, but even that is not a very accurate test as blowby gases are vented through the breather hose. The best test afterall may be cold-starting ability.

BTW, I had a brief look at your power steering service pictorial. Recently I came up with a more complete way to change the fluid and that is after sucking out the reservoir, suck out any remaining fluid in the system through the low-pressure hose using the correct MityVac adapter. You will have to bleed the system afterward though. You do have very nice and informative pictorials. This is just a friendly suggestion.

Diesel Giant · #21 07-15-2006, 09:41 AM

The engine was stone cold when I did the test. You will get the most blow-by at that point since the rings etc. have not yet reached maximum expansion to make a better seal.

cmp · #22 07-15-2006, 10:21 AM

Wow!

I did that very same thing to mine, and not only did the cap "dance"...it nearly shot through the hood...no joke. Not seriously burning oil though, so I guess I'm okay for now?

I think I'm gonna watch that again.

85chedeng300D · #23 07-15-2006, 01:47 PM

mine smokes at the oil filler hole, when cap is off when engine is hot but not when its cold. i guess its just smoke fom heat. or is it also blow by???? i already have 322K+ miles, all original? starts right up when its freezing cold as long as its glow plugged.

dieselnut14 · #24 07-15-2006, 05:03 PM

could the 0 blow- by be the effects of the bosio nozzels doing an efficeint job of spraying.I would like to know if the fuel economy went up with the new bosios,
let us know Russell if it made a difference.
Thanks. Peter

1984 300d 262 k

#25 07-15-2006, 05:13 PM

The problem is doing it stone cold. There is blowby, but it's all air. The oil isn't hot enough/churned enough to make the visible vapor.

Show a video of the blowby when the engine is at 82*c.

I can run my beat up engine stone cold and make it look blow-by free.

Brian Carlton · #26 07-15-2006, 05:27 PM

Quote:

Originally Posted by ForcedInduction

The problem is doing it stone cold. There is blowby, but it's all air. The oil isn't hot enough/churned enough to make the visible vapor.

Excellent point, Lance. I'm going to do a similar test on the SD.

BillA · #27 07-15-2006, 06:12 PM

sorry guys
bah, anecdotal blah blah (IMO)

normally connected there is negative pressure "at" the valve cover
with an open valve cover it is at atmospheric pressure at the valve cover opening
visible vapors will depend on a variety of circumstances; differential temps, relative humidity, etc
- if blowby is not observed with the breather tube still connected little is actually known as the breather tube is still sucking;
sure blowby is being observed (or not), but its better with some numbers

that being said, I have 2 617s; one shows nothing hot or cold, and the other is like Vesuvius
I 'do' thermodynamic testing and have some fine calibrated differential pressure meters
-> anyone have a spare cap to donate ?
I will tap it and generate some 'real' numbers under various conditions and RPMs

Hatterasguy · #28 07-15-2006, 06:22 PM

I think the important test is that if the engine starts when it gets "cold" in your area without giving you trouble the compression is fine. Thats the test that counts.

Really its all acidemic because unless you are going to spend at least $3k to rebuild the bottom end, you can't do anything about blow by.

Like I said my 617 chugs like a train, but it will start without a block heater in the mid teens. In my case it is just acceptable. I have been SOL on a couple of mornings last winter when I didn't plug her in.

Jeremy5848 · #29 07-20-2006, 01:49 PM

Quote:

Originally Posted by miner

The 617 has an oil seperator in the aircleaner that feeds back into the oil pan via a tube. At the end of the tube is a check valve that keeps oil vapors from getting sucked out of the pan by the air intake. (I don't know if blowby gasses can get into the lower oil pan. I wouldn't think so, normally, but if so then it is possible that people with very low blowby have a broken check valve so that all their blowby gasses are escaping into the air intake via this drain tube.)

Interestingly, one of the things that the 1985 California version lacks is the oil return line at the bottom of the air filter housing. Any oil that accumulates just sits there and waits to be mopped up at air filter change time.

Nonetheless, and in spite of the blowby (much more than DG's fine example), my car (212,000 original miles) uses no oil between changes (3000 miles), or at least not enough to be noticeable. It starts easily when cold, although that's a relative term -- it doesn't get cold here as far as this ex-Wisconsinite is concerned. At Christmas I'll be in snow country and will see how it does then (with DG's radiator hose engine heater kit).

Jeremy

Diesel Giant · #30 07-22-2006, 06:30 PM

As soon as I get one in I will do a video so those that don't know can see a car with lots of blow by.

Anyone in Atlanta got one to use as a candidate?