Oil in intake and head intake passages

[Jack O.]

Hi everyone,
I pulled my intake manifold ('69 427/435 but I'm running an LS6 intake) and have found oil in the intake as well as in the intake passages of the heads. When I peer into the intake passage I can see the top of the valve is very gunked up - I assume from the oil or is this normal? Does the oil indicate that the intake is not sealing sufficiently at the head. It does not leak anti-freeze but I believe it has been leaking oil at the front and back of the intake.
Thanks,
Jack

[Joe L.]

Re: Oil in intake and head intake passages

Hi everyone,
I pulled my intake manifold ('69 427/435 but I'm running an LS6 intake) and have found oil in the intake as well as in the intake passages of the heads. When I peer into the intake passage I can see the top of the valve is very gunked up - I assume from the oil or is this normal? Does the oil indicate that the intake is not sealing sufficiently at the head. It does not leak anti-freeze but I believe it has been leaking oil at the front and back of the intake.
Thanks,
Jack

Jack-----


This condition usually indicates oil leakage at the interface between the cylinder heads and intake manifold. It can be an ABSOLUTE BEAR to correct, too. I seriously doubt that you'll correct it by just installing new intake manifold gaskets, but that's a "first step" in what may end up being a long and frustrating process.

This condition can also be caused by excessive oil being drawn through the PCV system.

[Jack O.]

Re: Oil in intake and head intake passages

Hi Joe,

The intake was bought on ebay. Could it be the problem - maybe it was machined at some point or some such thing? Any other common causes?
Thanks,
Jack

[Duke W.]

Re: Oil in intake and head intake passages

It could also be caused by inadequate valve guide seals. A leak at a head/manifold port interface would probably cause some tuning problems - like not being able to get normal idle quality within the range of the idle adjustment screws due to the vacuum leak.

What is the rate of oil consumption? That's a key diagnostic.

The deposit buildup on the valves does no real harm. Actually it may improve flow.

My Cosworth Vega got down to a quart in less than 200 miles before I finally pulled the head for a refresh- and there was a lot of coked oil buildup on the valves and combustion chamber surfaces. The valve seals were shot and the guides badly worn.

The refreshed head doesn't run any better (and the deposit build-up didn't bother the HEI before the refresh), but now it doesn't smoke and smell so bad.

I suggest you thoroughly audit the PCV system - make sure it has correct components - clean and properly connected. If it checks out and your oil consumption is no more than a quart every 500 miles, don't worry about it.

Duke

[Joe L.]

Re: Oil in intake and head intake passages

Hi Joe,

The intake was bought on ebay. Could it be the problem - maybe it was machined at some point or some such thing? Any other common causes?
Thanks,
Jack

Jack-----


Machining is a possible problem. However, I once had this problem with a small block that I knew had never had the manifold machined and knew had never had the heads machined. So, it can happen with no manifold or head machining, at all. Generally, you can tell by looking at the cylinder head mating surface of the manifold if it's been machined.

In my opinion, this problem can be caused by a BLOCK that's "off". This can occur even from the factory. I'm pretty sure that's what happened in my case, even though I've not be able to confirm it.

[Jack O.]

Re: Oil in intake and head intake passages

Duke,
Doesn't use oil or smoke however the idle is terrible and the exhaust fumes at idle are overpowering. I smell of gas whenever I idle the car in the garage.

[Joe C.]

Re: Oil in intake and head intake passages

Duke,
Doesn't use oil or smoke however the idle is terrible and the exhaust fumes at idle are overpowering. I smell of gas whenever I idle the car in the garage.

Jack,

Your profile says you're 47 years old; maybe you got into cars at a late age.........after cat converters. The scenario that you describe is normal. Your eyes should begin to tear after not too long, too, and, yes, your clothing will exude that nice exhaust fragrance afterwards. Only real men smell that way! Remember that if/when you are out "trolling".

Also, if you've had a particularly bad day, you can also try the above test with the garage door closed. Tell a friend to drop by later to turn the engine off, and call 911.

Actually, a simple test for any of the above three possibilities is the following:
1. Warm up engine, and drive in a lower gear (pref 1st) to about 5000 RPM.
2. Close throttle and look in rear view mirror.

Note whether you left a trail of smoke behind, and which tailpipe it emanated from, if possible.

If you are not "using" oil, then you might be describing the normal gasoline residue left behind inside of your intake runners. There is always normally a slight film of unburned gasoline in the intake passages.....it will never be "bone" dry. If you have a problem, it will show up in the above test. You would almost certainly be consuming oil at an abnormal rate of 1 quart/200-1000 miles.

Joe

[Duke W.]

Re: Oil in intake and head intake passages

Duke,
Doesn't use oil or smoke however the idle is terrible and the exhaust fumes at idle are overpowering. I smell of gas whenever I idle the car in the garage.

I don't know what you mean by "terrible", but a L-71 should idle at about 900 with a little lope, but the idle should be stable.

Have you converted the ported vacuum advance to full time?

Duke

[Joe L.]

Re: Oil in intake and head intake passages

Duke,
Doesn't use oil or smoke however the idle is terrible and the exhaust fumes at idle are overpowering. I smell of gas whenever I idle the car in the garage.

Jack-----


If you've removed or rendered inoperable the AIR system, that will MARKEDLY increase the level of exhaust fumes. I can tell you that, FOR SURE.

[David J.]

Re: Oil in intake and head intake passages

I am curious ! How much oil is being consumed in a thousand miles? If the value guides are suspected wouldn't a leak test of the valve guides/seals be in order? Also what do the plugs look like?
As far as the raw fuel smell goes, what size of carb is on the motor ?

I to have experienced an intake gasket/manifold sealing problem and the problem was with the intake. Even after machining the manifold the problem was still not corrected and I had to replace the manifold. For the record the manifold was the original manifold on the LS-6 I was working on.

[Joe L.]

Re: Oil in intake and head intake passages

I am curious ! How much oil is being consumed in a thousand miles? If the value guides are suspected wouldn't a leak test of the valve guides/seals be in order? Also what do the plugs look like?
As far as the raw fuel smell goes, what size of carb is on the motor ?

I to have experienced an intake gasket/manifold sealing problem and the problem was with the intake. Even after machining the manifold the problem was still not corrected and I had to replace the manifold. For the record the manifold was the original manifold on the LS-6 I was working on.

David-----


I once tried THREE different intake manifolds on a small block that had this problem, including the original manifold and 2 NEW replacement manifolds.

I also tried TWO different sets of heads, the originals and a set of NEW GM replacements with all NEW GM valves, etc..

I tried just about every type of valve seal known to man, from stock 0-ring to Perfect Circle all-Teflon and everything in-between.

I tried just about every type of intake manifold gasket, including stock GM plus those manufactured by every major gasket manufacturer.

I tried every type of sealer from Permatex #2 to a gasoline-resistant special flurosilicone RTV (VERY expensive and hard-to-find).

I tried using an aerospace RTV PRIMER (VERY expensive and hard to find) in order to improve adhesion of the RTV.

I finally decided the problem had to be the rings (even though that would have no seeming relation the presence of oil in the intake manifold ports). So, I checked piston-to-bore clearances, lightly honed the cylinders to break the glaze, and installed new Perfect Circle Moly ring sets.

NONE of the above steps caused even the slightest difference in oil consumption or the "wet port syndrome".

[David J.]

Re: Oil in intake and head intake passages

David-----


I once tried THREE different intake manifolds on a small block that had this problem, including the original manifold and 2 NEW replacement manifolds.

I also tried TWO different sets of heads, the originals and a set of NEW GM replacements with all NEW GM valves, etc..

I tried just about every type of valve seal known to man, from stock 0-ring to Perfect Circle all-Teflon and everything in-between.

I tried just about every type of intake manifold gasket, including stock GM plus those manufactured by every major gasket manufacturer.

I tried every type of sealer from Permatex #2 to a gasoline-resistant special flurosilicone RTV (VERY expensive and hard-to-find).

I tried using an aerospace RTV PRIMER (VERY expensive and hard to find) in order to improve adhesion of the RTV.

I finally decided the problem had to be the rings (even though that would have no seeming relation the presence of oil in the intake manifold ports). So, I checked piston-to-bore clearances, lightly honed the cylinders to break the glaze, and installed new Perfect Circle Moly ring sets.

NONE of the above steps caused even the slightest difference in oil consumption or the "wet port syndrome".

WOW ! Isn't it amazing the different experiences we each have in this hobby.

[Michael H.]

Re: Oil in intake and head intake passages

Jack-----


Machining is a possible problem. However, I once had this problem with a small block that I knew had never had the manifold machined and knew had never had the heads machined. So, it can happen with no manifold or head machining, at all. Generally, you can tell by looking at the cylinder head mating surface of the manifold if it's been machined.

In my opinion, this problem can be caused by a BLOCK that's "off". This can occur even from the factory. I'm pretty sure that's what happened in my case, even though I've not be able to confirm it.

I agree with Joe on this. I've seen this a few times over the years. One I vividly remember was a 66 425 HP car that showed the same oil trail in the intake runners. Even after a complete engine rebuild, it still used about one quart per 100 miles.
If the intake gaskets were changed, the car would run without using oil for a few hundred miles but then, the oil consumption and blue exhaust would return. The block and heads had never been machined.
Eventually changed the intake manifold, thinking possibly it had a problem. The new (excellent used) manifold had never been machined.
Unfortunately, the excessive oil consumption returned within a few hundred miles. Fresh gaskets were the only thing that corrected the problem temporarily.
Unfortunately, the owner sold the car before I had a chance to figure out the actual cause of gasket failure. Had to be something machined incorrectly somewhere from new.

Excessively machined block deck or head surfaces can definitely cause this problem.

[Joe L.]

Re: Oil in intake and head intake passages

Hi everyone,
I pulled my intake manifold ('69 427/435 but I'm running an LS6 intake) and have found oil in the intake as well as in the intake passages of the heads. When I peer into the intake passage I can see the top of the valve is very gunked up - I assume from the oil or is this normal? Does the oil indicate that the intake is not sealing sufficiently at the head. It does not leak anti-freeze but I believe it has been leaking oil at the front and back of the intake.
Thanks,
Jack

Jack-----


The machine shop linked bellow MIGHT be able to correct the problem. However, I fully expect the machining operations are time-consuming (and, therefore, expensive). Click on "intake manifold machining".

http://www.fowlerautomotive.com/

[Joe L.]

Re: Oil in intake and head intake passages

Hi everyone,
I pulled my intake manifold ('69 427/435 but I'm running an LS6 intake) and have found oil in the intake as well as in the intake passages of the heads. When I peer into the intake passage I can see the top of the valve is very gunked up - I assume from the oil or is this normal? Does the oil indicate that the intake is not sealing sufficiently at the head. It does not leak anti-freeze but I believe it has been leaking oil at the front and back of the intake.
Thanks,
Jack

Jack-----


One other thing: check the centering of the tappings in the cylinder head for the manifold bolts with the holes in the manifold. Make sure that the bolts do not "bind" with the holes in the manifold due to poor alignment. If this occurs, you will note galling or thread marks, usually on the upper side of the manifold bolt holes. If this condition occurs, it means that the manifold, cylinder head, or block is "off" due to machining problems. In this case, you will also note that the manifold bolts will not turn down or out by hand; you will need a wrench all the way.