What does engine blowby mean?

[bigduby]

I am adding this in the diesel section to see if anyone can help me understand this information from my survey. It appears that one engine had a higher reading than the other and I don't know what to make of it. Can anyone clarify this?

Thanks.

 

[jrirvine1]

Means oil is blowing by around the pistons and rings, typically associated and is a symptom of bad compression. Blue smoke at start up is usually seen when the oil gets into the combustion chamber.

 

[sprink56]

Means the piston rings are nearing the end of their life span....they are not sealing the gap between the piston and the cylinder wall as they should.

 

[jitts3]

Means oil is blowing by around the pistons and rings, typically associated and is a symptom of bad compression. Blue smoke at start up is usually seen when the oil gets into the combustion chamber.

NO. Blowby is the compression and combustion blowing past the piston rings presureizing the crank case. This is why we have blowby tubes on trucks. At idle small amount of smoke/oil vapor comes out. I guess on boats its caught and recycled somewhere. Otherwise your engine room would fill up with the stuff? On a gas engine it it pulled in to the intake thru the PCV valve and re-burned. Not possible in a diesel due to being turbocharged. The intake is under pressure, not vacume.
This does cause an engine to consume oil too. So he's right there.
Now here is where I don't know if I'd worry. I never measured blowby before. It is measured by 1.5 x engine Hp. So is a 200 diference alot? Compared to? Can't help there. Sorry.
EDIT: ALL engines have blowby. The older they are the more they have.

 

[sprink56]

NO. Blowby is the compression and combustion blowing past the piston rings presureizing the crank case. This is why we have blowby tubes on trucks. At idle small amount of smoke/oil vapor comes out. I guess on boats its caught and recycled somewhere. Otherwise your engine room would fill up with the stuff? On a gas engine it it pulled in to the intake thru the PCV valve and re-burned. Not possible in a diesel due to being turbocharged. The intake is under pressure, not vacume.
This does cause an engine to consume oil too. So he's right there.
Now here is where I don't know if I'd worry. I never measured blowby before. It is measured by 1.5 x engine Hp. So is a 200 diference alot? Compared to? Can't help there. Sorry.
EDIT: ALL engines have blowby. The older they are the more they have.

You are correct. What threw me off was the signature that listed 350 Chevy's:thumbsup:

 

[jitts3]

But still, the unit of measuer they are using to me means nothing. To me bad blowby is when the damn thing disapears in smoke out the oil fil and dipstick tube. Had this engne blow oil out the dipstick tube before rebuilding it. 425 CID Cadillac

 

[bigduby]

So the biggest question is what does that 400+ number really mean? Its hard to know what is normal and what is a warning sign when you don't have anything to compare it too or any knowledge of the "norm". Also, if it is signs of wear, is it something that can be fixed when it gets too bad? This is on a cat 3116 350HP engine.
Thanks again.

 

[fc3]

You have to ask Caterpillar. They built the engine, designed the test, and know how to interpret them. That should be part of the survey.

 

[osd9]

....... I guess on boats its caught and recycled somewhere. Otherwise your engine room would fill up with the stuff? On a gas engine it it pulled in to the intake thru the PCV valve and re-burned. Not possible in a diesel due to being turbocharged. The intake is under pressure, not vacume.
........

The WalkerAirseps handle the blowby gases....You can read how they work here....hit the Play button...

 

[bigduby]

Thanks everyone for the info. I did finally get to talk to the Cat tech manager and get some answers. I appreciate the explanations, I am trying to learn this diesel stuff on the fly.. and eventually do my own maintenance if all works out with the sale of this boat.

Thanks again...

 

[jitts3]

So the biggest question is what does that 400+ number really mean? Its hard to know what is normal and what is a warning sign when you don't have anything to compare it too or any knowledge of the "norm". Also, if it is signs of wear, is it something that can be fixed when it gets too bad? This is on a cat 3116 350HP engine.
Thanks again.

New "holes" This is cylender sleaves, piston, piston rings, connecting rod, and bearings.
It would come as a kit pre-assembled. Basiclly rebuilding the engine.

The WalkerAirseps handle the blowby gases....You can read how they work here....hit the Play button...

Thanks. Was wondering.