Hi,
On my '73 (350sb w/ AT) I can cruise all day at 70 MPH (about 3000 RPM) and scarcely use 1 quart of oil in 3000 miles. But if I cruise at 75 MPH (about 3200 RPM) it sucks up about 1 quart every 300 miles! I've seen this before on other older sb chevys, above a certain speed the oil disappears fast. Doesn't seem to leak anywhere, the motor stays pretty clean. PVC is fine, breather on one valve cover, valve to manifold on the other. No evidence of blowby at breather. Any idea what causes this? And what can I do to prevent it (besides slowing down, I don't wanna do that!)? Thanks,


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-ibjoe
now: '73 LT1; '79 Z28
then: '67 coupe; '88 IROC; '95 Z28

My 69 396 acts very similiar. I have one of these crackcase evac systems so I'm guessing at high RPM I'm sucking the oil out of the breather with the exhaust. I don't have any baffles (or whatever they're called) on the valve cover. I'll probably install a regular PCV system and see itf anything changes.
But if you're having the same problem, myabe something else is happening on mine too.
I'll look forward to hearing opinions here!
Joe

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69 396 w/SS Trim, B&M TH400, 3.55 12 Bolt Posi, Blue w/White Z28 Stripes, Chrome Rally Wheels
Badboatdude@CS.com
69 Pics http://albums.photopoint.com/j/AlbumIndex?u=1506559&a=11674961

Many times high speed oil consumption is caused by oil buildup in the heads...the oil cant drain fast enough from the heads and it starts going in the valve guides...the best valve seals can only do so much when they are submerged in oil. One thing that helps is to take a die grinder and clean up the oil drain back passages in the heads. A hi-volume oil pump only makes it worse. My instructor in advanced auto shop back in college (also a dirt track racer and engine builder) said that he has seen hi-volume oil pumps increase oil consumption by 50% in some of his dirt track motors...the small black chevy has a good enough oiling system it doesnt need a hi volume pump in my opinion.

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375hp 78 Chevy truck
77 Chevy Nova
95 Chevy Lumina 3.4L
and building a 78 Nova

I've got a high volume oil pump as well.
Hmmmm. Maybe I should start putting things back toward stock!
Joe

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69 396 w/SS Trim, B&M TH400, 3.55 12 Bolt Posi, Blue w/White Z28 Stripes, Chrome Rally Wheels
Badboatdude@CS.com
69 Pics http://albums.photopoint.com/j/AlbumIndex?u=1506559&a=11674961

[This message has been edited by Joe G (edited 03-01-2001).]

Travis, what an awesome idea! That reminds me of [story] when I bought this car, the guy seemed happy to sell it for what seemed an unusually low price. I was driving happily, stopped at a light, all of a sudden big cloud of smoke engulfed car, couldn't see 2 feet! People yelling at me for polluting, I thought I blew the motor or something. I shut it off and pushed to side of road, opened hood, checked water, oil, etc. everything OK. 10 minutes later tried starting again, ran fine! For about 10 more minutes, then big smoke cloud again! After a week I finally figured it out, the oil return from heads was clogged with sludge, cleared it with a straightened coathanger, problems all gone! huh. btw, it was a ford, 289.

Anyway, that sounds like a good posibility, oil getting under the valve covers faster than getting out again, then getting sucked away via valve guides. I know the passages are clear, so how can I test for or fix this? Maybe attach a drain at lowest point on valve cover, run back to pan (or container to check).

Thanks for the idea!

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-ibjoe
now: '73 LT1; '79 Z28
then: '67 coupe; '88 IROC; '95 Z28

I am not sure how you would test that...but it wouldnt hurt to atake a look at the passages...occasionaly chevy would have some heads that came out with an amazing amount of casting flash in them...882's seem to be the worst ones. I spent several hours on the last set I had removing tons of casting flash from oil drain holes and the valve bowls...these heads were the worst ones I have ever seen.

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375hp 78 Chevy truck
77 Chevy Nova
95 Chevy Lumina 3.4L
and building a 78 Nova

You guys bring back memories of my old 1963 Merc Meteor that I bought off my Trooper buddy years ago. The one that died until I put a new $5.00 coil on it. Well, I do remember that the engine in it was sooo clogged up that when I cleaned it out I put a quart of diesel in it just before an oil change and rev'ed it up some til it got oil on the points and died. You would not believe what came out of the pan. I removed the road draft tube breather assy. and cleaned and removed what looked like a copper "Brillo pad" that was soo crudded up that it couldn't breathe.

I figure some tight-a-ssed old man had the car and was too tight ta change the oil and because all four corners of it was dinged like somebody couldn't hit a garage door opening.

IMHO, de-crud your engine with a quart of Marvel Mystery Oil or diesel like I did and see if it doesn't help. pdq67

pdq67, I know that story. We just did two cars, an Astro and a Muskrat. The Astro had a ton of sludge in the pan, but pouring diesel through the motor helped break it up. The Muskrat was a different story. I pulled the pan and scooped out the oil. It was the new "Betty Crocker" weight. Since I figured the motor could not have like this very much, I pulled the pistons. You could hold each rod and shack it hard, and still not have the piston move!

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Mark

1992 Firebird 355/Six Speed (Soon to be LT1)
1991 RS 350 / 700-R4
1987 Toyota Pickup 383 / 500 + HP 10.963 @ 119.95 Slicks / 11.997 @ 114.23 Radials
"Speed KILLS, so drive a FORD and live forever!"
http://personal.lig.bellsouth.net/~racer383/

Member of the "unwanted" 3rd Gen group.

Thanks for the story, pdq. I don't think sludge is the problem though. I've had the covers off, and it looks clean. The oil is always so clean sometimes it is hard to see it on the dipstick! I change it every 3K, and usually sacrifice a qt of new oil, pour 1/2 qt in each valve cover after pulling the plug, to flush as much old oil as possible out. Naw, motor is real clean inside. I'm still considering Travis' idea of oil is collecting under covers and spilling over guides, maybe too much casting flash like he says. I'm thinking of punching a hole in each valve cover below the valve guide line and running a hose to a catch can, see what I collect, does that reduce consumption..

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-ibjoe
now: '73 LT1; '79 Z28
then: '67 coupe; '88 IROC; '95 Z28