How to Measure Blowby - PeachParts Mercedes-Benz Forum

veg_burner · #1 03-21-2005, 10:48 PM

I've read in a couple of threads about looking for a 'sudden increase in blowby' or somesuch. Does this mean how much does it smoke or??

billrei · #2 03-21-2005, 11:00 PM

The only way I know of checking blowby is to remove the oil cap while the engine is idling. If it does not look like Old Faithful your in good shape!! Seriously, if you have a large volume of air rushing out that means that air is escaping around the rings and into the crankcase.

Wasuchi · #3 03-21-2005, 11:11 PM

I think I've read somewhere that there is some sort of gauge to measure blowby on some engines (basically a pressure gauge). I don't think it'll work on on a 617 or anything like it because of the way the shutoff is setup.

barry123400 · #4 03-22-2005, 01:48 AM

Do not suspect there is a standard for blowby but may be wrong. The tips on this site to see how long the engine runs with the vent tube hole closed off with your finger would give a pretty good indication I suspect. Think if engine runs any more than fifteen seconds it's in pretty good shape I recall. Otherwise it's probably just experience. If I wanted to check I might be able to do a modification of my carb syncronizer that now reads suction pressure to read the exiting pressure coming out of valve cover port. That would only be useful though if made to function in comparing it to another simular engine until one built up a comparison file. But most of the times I think I know something the wife is kind enough to correct me.

Unfortunatly she's out tonite.

leathermang · #5 03-22-2005, 07:42 AM

There is both an instrument and a standard listed in the Mercedes Factory Shop manual.

Pete Burton · #6 03-22-2005, 08:10 AM

Quote:

Originally Posted by leathermang

There is both an instrument and a standard listed in the Mercedes Factory Shop manual.

right you are Greg, but I'm too cheap to buy that instrument

I've thought of this before but haven't done it yet: Cut a plastic soft drink bottle with a taper that will fit tight on the oil fill hole. Get a 30 gallon garbage bag and duct tape it tight to the end opposite the taper. With engine idling warm and stopwatch at the ready, jam the taper in the hole, probably with some type of rubber ring to get a tight seal. Measure the time to inflate the bag so it stands up straight. This will give an approximate flowrate that can be compared to the MB spec (I've seen it too, it's very near the beginning of my motor manual). Also, if several of us do a similar experiment we may easily be able to develop some sort of a baseline for relative comparison. I suppose the onus is on me to actually do this on the weekend.

leathermang · #7 03-22-2005, 08:21 AM

That plastic jug is not going to LOOK very good.. Remember , you are working on a MERCEDES....
How about using an old oil cap and tapping it ?
What is that garbage bag going to smell like when it contacts your exhaust pipe ? How fast will it stop the engine from running when sucked into the intake ? How much mess will it make when it " hits the fan" ?
Stop me , Stop me ! this is too much fun.

Pete Burton · #8 03-22-2005, 08:26 AM

Greg, you are probably the only one here who could inflate the bag with hot air faster than the car!

Hatterasguy · #9 03-22-2005, 10:08 AM

You will know it when you see it.

ajb · #10 03-22-2005, 10:53 AM

What about asking a local politican "how to measure Blowby"?

It would seem many of the ones I've heard and seen seem to have grasp of this concept!

A. Berzins

boneheaddoctor · #11 03-22-2005, 10:59 AM

If when you pull the breather tube off with the car running and you have visons of a steam locomotive going up a mountain...you might have a problem....some misty blowby will be normal.

Brian Carlton · #12 03-22-2005, 11:02 AM

Quote:

Originally Posted by Pete Burton

Cut a plastic soft drink bottle with a taper that will fit tight on the oil fill hole. Get a 30 gallon garbage bag and duct tape it tight to the end opposite the taper.

Hey Pete,

Why bother with the oil fill cap? Why not just use the breather hose? You would have to plug this hose anyway, by your method.

barry123400 · #13 03-22-2005, 11:40 AM

Timing the bag sounds good as with little effort it could be left a little away from the car with an extension hose. Old breather hose with more hose coupled on ought to work well. My modification of syncro device akward at best as have already made too many adapters to fit various carbs like the zeniths without trying to figuring out a way to use it in a reverse application rube goldberg style. Thanks leathermag for the correction as was not aware there was a standard for these engines. My excuse this time was the wife was not home to correct me. Really though still do not have a good set of manuals yet. The best part of petes ideal is it is very simple and accurate enough I believe. Also liked the ideal of taking an old oil cap and modifiying it as perhaps the greater tube size comes in to play causing less restriction for airflow but think not particularily relevant in this application. Anyways hope pete patches something together and lets us know. My engines at present time have pretty minimal blowby. Some of course but not substantial. Also test temperature of engines must be comparable for each test for any accurate chart to be developed. No reason I can think of for it not to fly.

Good thinking pete and others. In fact the only difficulty when posting is perhaps the references to your bag. Someones bound to jump on it.

cgryphon · #14 03-22-2005, 12:28 PM

Thinking about blow-by on the 240D this weekend I decided to try the “tea kettle test”. Take off the oil cap and set it back over the hole, engine at idle. My result was a slight “tea kettle-ing” that is to say the cap was rattling a bit, but was in no danger of falling or being blown off. I did this with a cold engine, which I guess is not the way to do it. I plan on trying it again sometine after a bit of a drive.

My question is; why do I want to know this? I already own the car so……if it’s good (how ever you define that) that’s great. If it’s not so good, or bad, what am I supposed to do about it, short of tearing the whole thing apart? Can blow-by be improved (not corrected) through addressing simple issues?

This is all I could find on the online manual:

[http://skinnerbox.steaky.org/Service/W123/w123CD2/Program/Engine/615/00-310.pdf]

I especially like the part where it says “The engine ventilation systen (sic) is closed and maintenance-free.”

Clay

Eric Eliel · #15 03-22-2005, 12:32 PM

Read this thread:

Blow By Specs Listed Below

Find yourself an old natural gas meter, that will measure the blowby.

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