Engine blow-by test, Blow a bag of blow-by - PeachParts Mercedes-Benz Forum

junqueyardjim · #1 07-09-2007, 01:41 PM

Someone posted yesterday that the best test of engine blowby is with a garbage bag. So I followed another post where the writer was going to test his cars today with a garbage bag. And I wrote that I would do the same. Well I tested mine this morning and now I can't find that thread back and so I decided I would start a new one. Shouldn't mess up some other persons thread with something like this. So the question or project is to measure the amount of time to really fill a 30 gallon garbage bag with blowby. Not a real difficult project for a warm morning. I did it by borrowing a 30 gallon garbage bag from the laundry room. I pulled the hose from the air cleaner grommet, started the car, took the garbage bag in hand and inserted the hose, now above the top of the radiator. It took 2 minutes to get the garbage bag really hard. I held it for a couple more minutes and it didn't seem to get any harder. So, since it didn't stall the engine I presume that the bag developed a leak, though I did not notice a leak. That was on my 85 300D Turbo 617. Then I performed the same test on the 84. A like vehicle, though it is an 84 300D Turbo 617. This is the junkyard car I got from BioPete in Nashville in April. Anyway this car, I ran it for 5 minutes and only had a small blip of air in the bag at that time. I have noticed before that this engine just does not have any blowby. We checked the compression right after we got it started and adjusted the valves. We think it had not been run for 3 or 4 years. Compression was 450 on 3 cylinders, number 2 and 4 were a bit lower, like 375 and 400. Car runs very well, though when starting it cold, even on these summer days, it runs very rough for a couple of seconds after the glow plugs cool off and before piston temperature gets hot. What do you think might be causing that low compression on an engine with no blowby.

1983/300CD · #2 07-09-2007, 01:47 PM

Unplug a vacuum line and retest if you want to see the bag fill.

The compression test is what you should be worried about.

vstech · #3 07-09-2007, 01:49 PM

if ther's no blowby, low compression has to be the valves. you must have a burned exhaust or intake valve. or the vlaves need better adjustment, or the cam is shot.

vstech · #4 07-09-2007, 01:50 PM

Quote:

Originally Posted by 1983/300CD

Unplug a vacuum line and retest if you want to see the bag fill.

The compression test is what you should be worried about.

Uh, what vacuum line would affect CCV?

junqueyardjim · #5 07-09-2007, 02:02 PM

Both cars have the vacuum hooked up, though the door locks are not working on the 84. Do you think I can get rid of all that blow by on the 85 by eliminating the vacuum. Could be, but I don't think so, However, I will try it tomorrow. Maybe this evening if it doesn't rain. I also suspect the valves to be the problem with the compression.

Jeremy5848 · #6 07-09-2007, 02:06 PM

The original thread was

Drive car for over half a day, it shuts off!?!

My '87 300D W124 test is shown in that thread as posts 10 and 11. With the '87, the bag filled in 3 minutes, but not tightly -- see the photos in that post. I'll test the '85 this evening and post results for it.

As regards air being sucked into the engine and then blown out, thus increasing apparent blow-by, the vacuum pump vents into the crankcase, doesn't it? Perhaps that is what 1983/300CD meant when he suggested unplugging a vacuum line. Are there other places where air could get into the engine?

Jeremy

vstech · #7 07-09-2007, 02:09 PM

on a turbo 617 the VP does indeed vent into the crankcase, however there is no way to disconnect the vacuum to prevent it. you could open the main vacuum line and cap it to prevent vacuum from entering the pump, but hardly worth it in my opinion.

1983/300CD · #8 07-09-2007, 02:11 PM

Why are we still going over this?

Blow-By curioisty questions

Jeremy5848 · #9 07-09-2007, 05:54 PM

Here are the results of the test for my 617.

Conditions
1. Air temp 80F
2. Engine warm after driving 20 miles in city traffic with a/c.
3. Car is 1985 300D-T, 617 engine, CA version w/trap cat, EGR disconnected for testing. Main vacuum line not blocked off. Car has 223,000 miles, original unrebuilt engine, minimal oil useage between changes and no smoke.

Results (see pictures)
The bag filled in 90 seconds. This is half the time that it took to fill the bag on my '87 car (603 engine). Given my '87's penchant for using a quart of oil every 1000 miles or so and smoking (oil smoke) upon acceleration, I was not expecting these results. (The problem with the '87 is probably worn valve guides and/or seals -- that will be confirmed later this week. Other possible sources have already been eliminated.)

There must be more here than meets the eye, ear, nose, and throat.

I'll try repeating the test with the main vacuum line blocked off to see if there is any change.

Let's see someone else's results posted here.

Jeremy

Scott98 · #10 07-09-2007, 09:02 PM

Quote:

Originally Posted by junqueyardjim

it runs very rough for a couple of seconds after the glow plugs cool off and before piston temperature gets hot.

Updated glow plug relays keep the glow plugs on for up to (I think) 3 minutes after the engine starts to fix this problem. You may want to consider getting one.

Scott

Jeremy5848 · #11 07-10-2007, 09:39 PM

I decided to repeat the test on my W123 car (1985 300D-T w/ trap cat) after disconnecting the vacuum pump and plugging the line. The purpose was to see if there was a leak in the vacuum system that was showing up as increased blowby. The short answer is: NO CHANGE.

The first two pictures show vacuum levels in the system before disconnecting anything. Next is a picture of the main vacuum line disconnected and a small rubber stopper inserted to plug the line. The final picture shows the garbage bag, tightly blown up in 120 seconds.

Clearly, the vacuum system in my car doesn't have anything to do with the amount of blowby. (YMMV) I also did a teakettle test and was surprised at the amount of jiggle and oil that sputtered out from under it (the plastic cap may be to blame). The bag-test blowby is twice that of my 124 car , even though the latter is the one with the oil-burning problem. Most interesting!

Jeremy

Diesel911 · #12 08-26-2009, 01:36 AM

Quote:

Originally Posted by Jeremy5848

I decided to repeat the test on my W123 car (1985 300D-T w/ trap cat) after disconnecting the vacuum pump and plugging the line. The purpose was to see if there was a leak in the vacuum system that was showing up as increased blowby. The short answer is: NO CHANGE.

The first two pictures show vacuum levels in the system before disconnecting anything. Next is a picture of the main vacuum line disconnected and a small rubber stopper inserted to plug the line. The final picture shows the garbage bag, tightly blown up in 120 seconds.

Clearly, the vacuum system in my car doesn't have anything to do with the amount of blowby. (YMMV) I also did a teakettle test and was surprised at the amount of jiggle and oil that sputtered out from under it (the plastic cap may be to blame). The bag-test blowby is twice that of my 124 car , even though the latter is the one with the oil-burning problem. Most interesting!

Jeremy

Maybe the Oil burnig issue is related to Problems with the Oil Rings and the Blow-by issues are related to problems with the Compression Rings.

I would also think that correct IP timing and good Injectors within specs would have an effect on Blow-By.

And, what role do Valve Stems Seals play in the Blow-by and Oil burning issues.

A lot of variables to consider.

compress ignite · #13 08-26-2009, 02:41 AM

Nah,'Can't ever have too much info!

Skippy · #14 03-14-2010, 06:57 PM

I did mine today.

Conditions
1. Air temp 48F
2. Engine moderatlely warm after driving about 6 miles.
3. Car is 1983 300D, 617 engine, federal version. Main vacuum line not blocked off. Car has just short of 311,000 miles, original unrebuilt engine, minimal oil useage between changes and no smoke.

Results

The bag filled in just over two minutes.