Blow by on a multifuel

[engineer233]

I know this is probably a rookie question but, what is blow by from a engine and is there a problem if it is a little smokey ?

 

[JCKnife]

I can't help you with the term but felt compelled to post:

1) I was in London last week! (quoting a roof)
2) Mine is a little smokey (but not much) and I run about 75% WMO
3) I was amazed today to find that, the engine is really not ANY louder with the exhaust pipe removed (including the J).

 

[Mike O]

Blow-by basically means that your rings, pistons, cylinders are worn. Blow-by is a condition where the compressed air fuel mixture and combustion gases are blown past the rings and pistons and into the crankcase. The result is low compression, oil consumption, and a pressurized crankcase that blows oil out of the filler cap, dipstick tube or wherever else it can go. A little leakage is normal but excessive blow by means you need a rebuild.

 

[engineer233]

Thanks Mike O . Mine runs great it just has some blow-by but nothing major. I was just checking it after I pulled my farm tractor home.

 

[TMNT]

I know this is probably a rookie question but, what is blow by from a engine and is there a problem if it is a little smokey ?

Strictly speaking, blow-by is a component of pressurized air-fuel mix that is blowing past the piston rings either during the compression stroke or during the power stroke, or both. The result is that you get a certain amount of combustion by-products into the crank case that contaminates the oil and increases pressure in the crank case. Blow-by at some small level occurs as a normal part of engine operation. It increases as the piston rings and/or cylinder wall wear over many hours of operation, or from overheating damage, or from dirty air getting past the air filter.

Now, for what you're probably really asking about, the draft tube or slobber tube, releasing crankcase pressure. The slobber tube hanging down on the right side of the engine is where pressure from the crankcase escapes. And yes, it's normal for there to be small amounts of oily vapor, maybe a drop or two of oil. If you're seeing actual smoke coming from there, that's an indication that you have some piston ring and cylinder wall wear, but it doesn't necessarily mean that you have a serious problem. It could and likely will operate for many more years that way. I see a good deal of steam and vapor from mine when it's cold and I'm only running for a few miles at a time. When I run it for an hour or more so that the oil has a chance to cook out all of the accumulated moisture, the steam goes away.

 

[engineer233]

That is exactly what I'm seeing. It is an oily vapor and may have a little steam in it. After your and Mike O's reply it makes me feel better now about my engine. Like I said it runs great it just has a little coming out of the slobber tube. I don't get to run it much though. Thanks guy's.

 

[Clay James]

They tend to get it when they idle a lot or are used at low RPMs. The TM even says to cure it, drive it hard on the road for a while. Both of my trucks have gotten it really bad a few times. My M109A3 did the other day when I decided to practice backing my M105A2 all the way down my driveway. That meant lots of low RPMs and idling. It started puking out the exhaust manifolds and turbo. I took it on a 10 mile drive and drove it harder than normal and it cleared up. My A2 did it really bad when I first got it, but it cleared up when I got it registered and took it on the road the first time. Of course if your rings are worn that's another story.

 

[Odyssey M]

This was a very informative thread. Thanks for the question and the constructive feedback!

 

[rbeasley66]

Hence the reason for the PCV, positive crankcase ventilation, system after the EPA got involved for cleaner running vehicles. All that stuff now gets sucked back into the intake, unfiltered, and burned in the cylinders. Called the CDR valve in a CUCV with the 6.2 engine also.