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What causes blowby?

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Old 06-29-2010, 12:36 PM
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Default What causes blowby?

The past year I have had breathers only on the car, no pcv valve, and the last few months, oil would be pushing out of the breathers bad. Burnt oil smell above 4k rpms, blowing oil, and even blew the dipstick out on the dyno. When I had the compression check done at a shop, they put a PCV valve back in, but it’s not hooked up exactly like factory spec (or so how I remember it was). Car holds idle a lot better now (more vacuum I guess), but oil can still be smelled when getting on it, just not quite as bad.

I am assuming its rings that are leading to excessive crank case pressure, but I am not sure. I did a compression check, and that turned out fine, 150 psi in all cylinders, except for #7, which had 145. Leak down test next? Thoughts, inputs?
Old 06-29-2010, 12:42 PM
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Originally Posted by AznMuscle
The past year I have had breathers only on the car, no pcv valve, and the last few months, oil would be pushing out of the breathers bad. Burnt oil smell above 4k rpms, blowing oil, and even blew the dipstick out on the dyno. When I had the compression check done at a shop, they put a PCV valve back in, but it’s not hooked up exactly like factory spec (or so how I remember it was). Car holds idle a lot better now (more vacuum I guess), but oil can still be smelled when getting on it, just not quite as bad.

I am assuming its rings that are leading to excessive crank case pressure, but I am not sure. I did a compression check, and that turned out fine, 150 psi in all cylinders, except for #7, which had 145. Leak down test next? Thoughts, inputs?

What year car? Miles? How exactly is the pcv system setup?

I think you should address your Pcv issues first, but blowing the dipstick out isnt a good sign, kinda surprised that you didnt blow oil out of the rear seal.
Old 06-29-2010, 12:46 PM
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You are correct, usually blowby is an indication of worn rings. Pretty typical with a LS1. Your compression is still decent. Slap an oil catch can on that bad boy and keep on truckin'.
Old 06-29-2010, 12:46 PM
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That is one thing I am worried about, and need to check next time the car is jacked up. Oil out of rear seal would be bad. 99, 103k miles. H/C set up for about 20-30k miles. PCV set up is driver side valvecover breather, PCV is there, hooked up to the TB. I'll try to find a camera and snap picstures today after work and get them posted on here so you can see. From what I remember the stock PCV looking like, the valve was on the passenger side. My passenger side breather is still there, just the driver side is now replaced with a PCV.
Old 06-29-2010, 12:47 PM
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Catch can has also been thought about. They aren't expensive, so I might as well.
Old 09-22-2012, 06:05 PM
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Originally Posted by AznMuscle
The past year I have had breathers only on the car, no pcv valve, and the last few months, oil would be pushing out of the breathers bad. Burnt oil smell above 4k rpms, blowing oil, and even blew the dipstick out on the dyno. When I had the compression check done at a shop, they put a PCV valve back in, but it’s not hooked up exactly like factory spec (or so how I remember it was). Car holds idle a lot better now (more vacuum I guess), but oil can still be smelled when getting on it, just not quite as bad.

I am assuming its rings that are leading to excessive crank case pressure, but I am not sure. I did a compression check, and that turned out fine, 150 psi in all cylinders, except for #7, which had 145. Leak down test next? Thoughts, inputs?
hate to bring back such an old thread, but i was googling some pcv stuff and stumbled across this. but your problem here would definitely be the breather only setup. imo its always best to run a catch can with a ls6 valley cover and the breather in the passenger side head. otherwise, as you noticed, you will get a lot of smoke making its way out of the breather and other gaskets. i just bought a 2nd car a few weeks ago and it has only 1 breather on the valve cover, which was smoking out of the breather. slapped on my catch can and cleared that right up



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