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How much Blowby is acceptable?

I

I Like Torque

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Least i'm pretty sure that's what it is called. When opening the oil filler cap and looking at how much smoke comes out at idle... keep in mind this is on a vehicle with 200k-250k miles on it... i saw one vehicle pouring out 3 feet of straight up steam, and another let out barely a 3 inch cloud from the top of the oil filler to the smoke.,
 
Blowby is oil mist and a little 'smoke'...

The old faithful geyser of steam is a dead engine that happens to run.

Somewhere I read of a 'water bucket' test. Something like taking the tube from the CDR or crankcase (valve cover) dip into the water and watch for bubbles or lack thereof.

Important to distinguish Steam from Smoke first..
 
Checking Blowby

On a warm running engine, pull off the oil fill cap. If no smoke or a very light haze comes out this is normal.
If it seems there is excessive smoke coming out, the piston rings or other parts may be very worn.
 
I can help out with one of my own videos...

A 6.2 with a dead #5 hole (confirmed after teardown). The 'paper over the hole' trick works pretty good.

Important to note the 'pulsing' effect on the paper- the cheapest tool ever. A reasonably healthy engine will not Chug like this.

http://www.youtube.com/watch?v=Y0rMAKU9fBU
 
the bucket test is described in detail in Heath's blog. Basically with the clear hose in the bucket when you rev the engine to 2k rpm you should see the water in the bucket rise up the clear tubing. If it blows bubbles that is really bad. FWIW mine with lots of blowby still passes the bucket test. Make sure the air filter is clean dirty one will give you a false reading and an oiled filter will do similarly.
 
You're going to get as many answers to this question as there are pebbles in a brook.

Here's Bill Heath's blog on the subject:

http://webcache.googleusercontent.c...cd=1&hl=en&ct=clnk&gl=ca&source=www.google.ca

My personal opinion?

On a daily driver, blowby is pretty much whatever it is. Meaning, you can have a lot of it and still drive it. You're not placing any serious load on the engine and it can limp along for a fair bit even if it's right at the end of it's life cycle.

However, if you have enough "blow by" that is is also puffing out of the oil dipstick tube or it fails teh "water test", you should be putting some serious thought into whether or not you want to subject that engine to loads such as trailer towing or high weight loads.....
 
Pull the cdr out at the turbo elbow with the truck running. The CDR can mask how bad it really is. While you have it out pay special attention to the fitting that goes to the cdr and see if there is ANY slime at all. Some drips of black oil normal. If you see even the slightest hint of peanutbuttery lookin stuff, pass on it. I looked at a 99 Burb with 44k original miles. I saw it was low on coolant in the jug which made me suspect. The oil on the dipstick was fine but that tiny bit of slime on the cdr fitting by the turbo elbow told the tale....
 
200-250K means the owner got their value out of the original engine. Cracks, head gaskets, and plain wear are real concerns not only for the engine but the entire truck. These can go black hole quick. Blowby only indicates ring condition and possible valve guide problems. The rest of the engine follows blowby wear but there are exceptions.

Puffs as said above are bad. They can also come from a cracked piston that is about to burn through.

Less is generally better, but, with this kind of miles be prepared to drop and engine, transmission, injectors, rear end, 2K in misc parts at it...

Trucks with 125K on them can be had for about the same money and may have fewer issues.
 
living in central NY and only spending 4grand, a 6.5/6.2 1991-95 with the cab corners and rocker panels all intact is literally 5+grand... its rediculous
 
My 1500 at 220K has very little blowby you could say none, but it's also a 1/2 ton & based on other indicators has lived a very unscathed easy life, mostly a grocery getter with the occasional bass boat behind it.
 
any pictures of the 93? definetly interested (drooling over the nv4500)... i'd pretty much be paying all i could at 4grand, as long as the tires and rims would get through a winter i'd be fine with that, stereo doesn't matter, and im sure i can get some gauges.
 
we should probably take this to PM but I have a set of 38.5s that came off it with aluminum rims. They are still roadworthy but ride like shit compared to the 35's. Read the whole thread on it. There are many many pics.
 
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