Oil in intake runners...
Thread Starter
Burning Brakes
Joined: Jul 2001
Posts: 1,160
Likes: 0
From: Ajax Ontario
Oil in intake runners...
My garage pulled my heads to fix (under warranty) a valve seal problem. They noticed oil coating the intake and are speculating that I'm drawing oil in through the PCV. I have a breather on the right bank (chrome open style filter, not the correct in the air cleaner variety) and the proper PCV fitting on the left bank.
Oil pressure has always seemed a little high (30 psi at idle, engine hot, 20w50 oil). Could this be the culprit?
Could it be a poor intake seal, that hopefully will go away with the reinstallation of the intake/heads?
Could it be related to the faulty valve seals? (Guides are perfect on the rebuilt L79 "double hump" heads)
Any other ideas?
Thanks!!
PS. Engine and heads have about 4,000 miles since full rebuild, hence agreed to fix for free....
Oil pressure has always seemed a little high (30 psi at idle, engine hot, 20w50 oil). Could this be the culprit?
Could it be a poor intake seal, that hopefully will go away with the reinstallation of the intake/heads?
Could it be related to the faulty valve seals? (Guides are perfect on the rebuilt L79 "double hump" heads)
Any other ideas?
Thanks!!
PS. Engine and heads have about 4,000 miles since full rebuild, hence agreed to fix for free....
Drifting
Joined: Mar 2000
Posts: 1,321
Likes: 2
From: Haysville Ks
Re: Oil in intake runners... (68shark)
When I replaced my intake , I put a little bit of the blue rtv on the threads of the manifold bolts. The intake bolts were new, If you reuse your old intake bolts, use a wire brush, or if you have a wire wheel on a grinder, use it to clean the threads first.
Burning Brakes
Joined: Dec 2000
Posts: 1,183
Likes: 2
From: Des Moines Iowa
Re: Oil in intake runners... (68shark)
Oil on / in all of the intake manifold runners indicates that you are pulling oil through the carburator, and yes this could be due to a PCV valve problem.
Your oil pressure doesn't sound too high to me, especially using a pretty thick grade of 20W50. Further, it's highly unlikely that high oil pressure would cause oil consumption any way, and in your case, I don't think you have a high oil pressure problem at all.
Bad valve guide seals will cause oil consumption and a good indicator of bad valve guide/stem seals is blue smoke at engine start up, especially after the engine has not been started for a day or more. Bad valve guide / stem seals will NOT result in oil in the intake manifold runners.
A bad intake manifold to head seal, will also result oil consumption, and can be identified once the intake manifold has been removed, by presence of oil on one or more intake ports of the heads and no or very little oil present in the intake manifold runners.
I hope this helps.
Your oil pressure doesn't sound too high to me, especially using a pretty thick grade of 20W50. Further, it's highly unlikely that high oil pressure would cause oil consumption any way, and in your case, I don't think you have a high oil pressure problem at all.
Bad valve guide seals will cause oil consumption and a good indicator of bad valve guide/stem seals is blue smoke at engine start up, especially after the engine has not been started for a day or more. Bad valve guide / stem seals will NOT result in oil in the intake manifold runners.
A bad intake manifold to head seal, will also result oil consumption, and can be identified once the intake manifold has been removed, by presence of oil on one or more intake ports of the heads and no or very little oil present in the intake manifold runners.
I hope this helps.
Thread Starter
Burning Brakes
Joined: Jul 2001
Posts: 1,160
Likes: 0
From: Ajax Ontario
Re: Oil in intake runners... (john's '81 mouse)
Thanks both for the feedback!
My PCV is installed in a set of Chevy chrome valve covers that are very well baffled. PCV itself seems ok. How could it be pulling oil in or more to the point, how do I correct this??
Thanks!
My PCV is installed in a set of Chevy chrome valve covers that are very well baffled. PCV itself seems ok. How could it be pulling oil in or more to the point, how do I correct this??
Thanks!
Drifting
Joined: Nov 2001
Posts: 1,469
Likes: 6
From: 68 427 4.11s Roadster
Re: Oil in intake runners... (68shark)
Oil pressure isn't the problem, mine is far higher with no problem.
If you haven't, get a new pvc and clean or replace the breather. The only way I know of for oil to get in the intake is throught the vacuum lines. You can look inside the vacuum line or stick a q-tip in there to see if its oily.
On Automatics this is the check for the vacuum modulator.
If the oil isn't draining out of the heads this could add to the problem, I don't see this with so little mileage on them though.
If you haven't, get a new pvc and clean or replace the breather. The only way I know of for oil to get in the intake is throught the vacuum lines. You can look inside the vacuum line or stick a q-tip in there to see if its oily.
On Automatics this is the check for the vacuum modulator.
If the oil isn't draining out of the heads this could add to the problem, I don't see this with so little mileage on them though.
Melting Slicks
Joined: May 2001
Posts: 2,131
Likes: 4
From: May help you? You can sure as hell try!
Re: Oil in intake runners... (68shark)
Have your shop perform a eak-down check , a simple compression check may or may not reveal rings that may not be sealing properly. Worn rings can result in excessive blow-by into the crankcase which in turn results in PCV "push over". This is where the crankcase pressure becomes higher than in your intake and the crankcase gases "push over" into the intake instead of pulling out of the crankcase like they're supposed to. Also, extended periods of operation at wide open throttle (you don't ever do this, do you?...shame on you!:jester ) can result in "push over" even if your motor's wear condition is fine. Also, make sure the "clean air side" (that's the side that vents your aircleaner or to atmosphere) is open and free flowing.
Also, check your intake gasket seal between the intake and cylinder head. It could be that intake runner vacuum is drawing oil in from the valley under the intake. You'd also probably have a rough idle from the vacuum leak.
Also, check your intake gasket seal between the intake and cylinder head. It could be that intake runner vacuum is drawing oil in from the valley under the intake. You'd also probably have a rough idle from the vacuum leak.
Melting Slicks
Joined: May 2001
Posts: 2,131
Likes: 4
From: May help you? You can sure as hell try!
Re: Oil in intake runners... (LemansBlue68)
Oops, just noted that your engine is newly rebuilt. If the problem persists and its not an intake leak, do the leakdown check anyway. There's always the possibility that the rings are not seated propery and aren't sealing.
Good Luck.
Good Luck.
Drifting
Joined: Nov 2000
Posts: 1,361
Likes: 0
From: Honolulu Hawaii
Re: Oil in intake runners... (68shark)
Could the oil be just remnant from when your new rings were letting excessive blow-by occur before they seated. The blow-by can kick-up quite a storm of oil laden air which is sucked up by the pcv. Just a guess. Forget this theory if the oil thing got worst as you broke the rings in.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Team Owner
Joined: Jul 2001
Posts: 61,415
Likes: 478
From: Here to make friends
St. Jude Donor '11, '16-'17
Re: Oil in intake runners... (68shark)
This happened to me with a truck I had a few years ago. Rebuilt 350, but I was getting oil into the air cleaner through the breather. One mechanic told me off the top of his head that the cylinders were egg shaped and I was getting too much blow by. The motor ran really well though, and I didn't have any oil on the sparkplugs, so I didn't believe that. The block wasn't original, but I had put the original intake, heads, etc back on it. My step father thought that it was the wrong intake and wasn't venting correctly. I don't know if I believe that either. I finally got rid of the truck. It still ran great, but was still pushing some oil back into the air cleaner. I've been curious all these years to know what actually was wrong. Now that I think about it, I don't remember sealing the head or intake bolts. Could that have been the problem?
Thread Starter
Burning Brakes
Joined: Jul 2001
Posts: 1,160
Likes: 0
From: Ajax Ontario
Re: Oil in intake runners... (The_Dude)
Thanks for all the replies!! Leak down test was done yesterday (just to check) and result is perfect. I will check the breather, but it's fairly new and don't think it's the problem. There is also a breather cap on my oil fill tube (68's, like c2's have an oil fill tube in the intake (not valve cover) and mine has a breather cap, not the standard cap. Glad to hear oil press. isn't likely the culprit because I don't really want to get into replacing the pump.
I'm hoping it may have been a faulty intake seal, but will check the pcv system for oil and keep an eye on it.
Is it possible rings aren't fully seated at 4,000 miles? Hyper. pistons, flat tops, stock 327 bored .30 over. Thanks!
I'm hoping it may have been a faulty intake seal, but will check the pcv system for oil and keep an eye on it.
Is it possible rings aren't fully seated at 4,000 miles? Hyper. pistons, flat tops, stock 327 bored .30 over. Thanks!
