Blow-by

[1992gen1_fan]

Hello, what is an "acceptable" amount of blow-by? After a drive there is a good stream of smoke from the blow-by tube. Its pretty much a constant stream, not blowing smoke rings of puffs. Its enough that when I park with the engine idling I can look out the passenger window and see the haze. The oil has about 2000mi on it and I'v added about 1qt of lucas since I'v changed it.
I sent a sample to blackstone labs for analysis when it was changed and everything looked good exept a very small amount of coolant and silica was just a tad high, all wear metals in spec at over 6k mi on the oil. It has had the blow-by problem for a few years but it seems more noticable, its usually worse in the winter.
Also, the engine always starts fine. What exactly would be causing the blow-by? I'm open to all suggestions thanks

[Sutter1stgen]

If your results came back well I wouldn't worry about it. I run a valve cover breather along with the factory one. That seemed to help when I was making full boost. I can see amconstant stream of smoke on mine as well. But not visible while in the truck!!!! That's odd. With my old set of twins I would have a lot of drive pressure and boost, which caused ambunch of blow by. That's why I went to 2 breathers. I also routed my draft tubes to the back of the t case now.

[1992gen1_fan]

I like the idea of routing the tube past the t-case. I might try to post a video of the blowby at idle, I don't really know anyone else in my area that I can look at thier truck and compare. I might be parinoid, just don't want to ruin the 'ol cummins. It usually starts getting worse around time to change the oil but it still has a couple thousand miles this go around.
Would a block test tell me anything for blowby?

[Sutter1stgen]

As I get close to a service interval mine smokes more as well. I don't know who's oil you run, but my personal preference is shell rotella triple protection. I noticed it didn't smoke or leak oil out of the original tube as soon or often as the other brands of similar price. I'm not saying run it. It just seemed to work for me. My dad runs nothing but shell in all his farm equipment as well. It's the only thing we agree on!! Haha. Mine used to drip oil at every shut down. And it would paint the side of my truck at hiway speed in the summer. I also didn't have overdrive at the time either, and had the engine screaming.

[1992gen1_fan]

I used to use shell rotella, I'v ran Conoco Fleet supreme HD the last several changes and like it fine so far. It does'nt stink like the rotella does. Thats basically the main reason I switched. I still run rotella in my tractor and just put up with the smell..

[edeus]

Hi,

I just make blowby test to my -89 Cummins, with that looking tester https://goo.gl/mw0nam.
I am not really happy with the results.
At the tdc all cylinders leak nearly 80%, but in all other postions leak was under 10%.
So i got huge leak in cylinder but just in tdc.

Engine runs smooth, it has power, does not smoke or burn oil. Oils look and smells good.
Should I take motor apart, re-ring it and take block and head to machining?

[spencerdiesel]

High boost (what Sutter1stgen said), worn rings/cyl walls can cause excessive blow-by. Probably not an issue in your case but idling for extended periods of time is about the worst thing a compression ignition engine can experience.

[spencerdiesel]

There is more blow-by on a cold engine in winter because metals contract, and more gases can get by the rings and into crankcase etc.

[matthewh]

I had read somewhere on here that the vacuum pump vents to the block, so "excessive" blow by maybe nothing more than an issue with your vacuum pump.

[spencerdiesel]

Good point