Compression good - plug fouling

[Ryanz]

Purchased my 72 K5 about a year ago. It had sat for about 13 years after being restored. It's fouling the #8 plug with sludge and oil. However compression is a solid 140. I have replaced guide seals as they were hard as rocks but that hasn't solved the problem. I hear some guys suggesting it could be an intake gasket but I have solid vacuum and truck runs nice when not fouled. The previous owner did put holly intake and carb on it. The rest is matching numbers block. The shop I trust recently did a bore scope and said there is scaring on #8 - but wouldn't that mean my compression should be bad if it's sucking oil through there? On the highway doing 65mph it will just about burn a litre per hour. Not near as bad when just cruising around the city. Would sure appreciate some suggestions. I'm being told it's more than likely a rebuild project this winter :/

[Blazer690]

Also like to know!!

[JMac11]

Good vacuum is an indication of a healthy engine. Probably a broken ring, probably an oil ring. Look for wear on top of the valves, that would indicate a worn guide, but the solid vacuum really eliminates that. If you can find one, they used to sell "non-foulers" that are basically and extention for your sparkplug to keep it out of the oil. My recommendation drive the stew out of it till it dies. Oil consumption is not the death knell of an engine by no means

[Ryanz]

Originally Posted by JMac11

Good vacuum is an indication of a healthy engine. Probably a broken ring, probably an oil ring. Look for wear on top of the valves, that would indicate a worn guide, but the solid vacuum really eliminates that. If you can find one, they used to sell "non-foulers" that are basically and extention for your sparkplug to keep it out of the oil. My recommendation drive the stew out of it till it dies. Oil consumption is not the death knell of an engine by no means

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[Ryanz]

Originally Posted by Ryanz

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Yes, vacuum sits around 16. It's not excellent but certainly passes would you agree. I've heard of the non fouler but haven't found one that is the right size yet - they're all for a much larger plug. I'll keep looking - thanks kindly for your help.
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[Valarius_Starchaser]

I would be willing to bet on the oil ring as well when it gets hot it goes through thermal expansion and lets oil by somewhere I would personally take that head off pull that piston do a ball hone in that bore new rings and let her rip let us know

[Ryanz]

Originally Posted by Valarius_Starchaser

I would be willing to bet on the oil ring as well when it gets hot it goes through thermal expansion and lets oil by somewhere I would personally take that head off pull that piston do a ball hone in that bore new rings and let her rip let us know

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[Ryanz]

Originally Posted by Ryanz

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Makes sense - the only thing that doesn't is the compression is strong. Shouldn't that show up in the test?
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[Valarius_Starchaser]

Thats where the thermal expansion comes in the crack or break in the ring expands and allows blow by but on the test it shows fine because between the rings at low temp it holds

another thing I could/have seen is a bad valve seat but with a decent 16psi vacuum that shouldn't be it is it a stable reading or does it fluctuate plus or minus 5psi?

[A1971Blazer]

Just a thought......... but you did clean the oil drain hole at the back of the head....right?
I've seen them get stopped up and oil will puddle around the valve stem and get sucked into the cylinder.

[cleszkie]

Two things to check:

1) Do you have an oil baffle under the PCV valve opening in the valve cover. If not, oil will get sucked into the engine, burned, and foul plugs. All plugs will not get fouled. It depends on the routing of the intake manifold with regards to the runners that are closest to where the PCV line dumps into the carb base. Ask me how I know this one!

2) If you have an auto tranny, check to make sure that the vacuum modulator is dry. If it is wet, good chance that you are sucking ATF through the modulator and into your intake manifold. The vacuum port for the tranny is on the back of the manifold, and may be directly connected to the No. 8 runner.

[hemi43]

Sounds like a perfect candidate for an LS swap, IMHO.

[Valarius_Starchaser]

Originally Posted by hemi43

Sounds like a perfect candidate for an LS swap, IMHO.

Fix one problem with 5 others perfect!

[Ryanz]

Originally Posted by hemi43

Sounds like a perfect candidate for an LS swap, IMHO.

Sorry for my ignorance - what is an LS swap again? I know I'm going to feel stupid when you give me the answer.
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[hemi43]

Originally Posted by Ryanz

Sorry for my ignorance - what is an LS swap again? I know I'm going to feel stupid when you give me the answer.
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Using a newer fuel injected computer controlled engine and its overdrive transmission like a 5.3 or 6.0. Technically they are Vortec and not an LS engine but come from the same family. IMHO, I will never own an older cabureted engine. My last trip with the blazer I averaged 24.6 MPG.

[Ryanz]

Originally Posted by A1971Blazer

Just a thought......... but you did clean the oil drain hole at the back of the head....right?
I've seen them get stopped up and oil will puddle around the valve stem and get sucked into the cylinder.

Sorry, I have never heard of this. Where can I do this?

[Ryanz]

Originally Posted by cleszkie

Two things to check:

1) Do you have an oil baffle under the PCV valve opening in the valve cover. If not, oil will get sucked into the engine, burned, and foul plugs. All plugs will not get fouled. It depends on the routing of the intake manifold with regards to the runners that are closest to where the PCV line dumps into the carb base. Ask me how I know this one!

2) If you have an auto tranny, check to make sure that the vacuum modulator is dry. If it is wet, good chance that you are sucking ATF through the modulator and into your intake manifold. The vacuum port for the tranny is on the back of the manifold, and may be directly connected to the No. 8 runner.

I assume by baffle you mean the rubber piece under the PCV valve - yes it is there and in good condition. Also checked the modulator and it is dry - son of a... Thank you for the suggestions. Looking more and more like it is a ring. Expensive fix for a guy who can't do it himself. (not a mechanic)

[Ryanz]

Originally Posted by hemi43

Using a newer fuel injected computer controlled engine and its overdrive transmission like a 5.3 or 6.0. Technically they are Vortec and not an LS engine but come from the same family. IMHO, I will never own an older cabureted engine. My last trip with the blazer I averaged 24.6 MPG.

Thanks - but want to keep it 100% original. It has original block which I think is worth keeping and restoring. Also, I don't drive it in the winter. The way I have it set right now you barely touch the key and it fires up, even after sitting for days. It gets about 18 mpg on the highway without the air conditioning running.

[A1971Blazer]

Originally Posted by Ryanz

Sorry, I have never heard of this. Where can I do this?

At the back of the head...under the valve cover....there is a hole cast into the head that lets the oil drain back down into the lifter galley and back down to the oil pan........it's directly behind the #8 cylinder...there's a lot of oil going to the rockers and it has to drain freely out of the top of the head or it puddles around the valve stem...thus getting sucked into the cylinder...

That may not be the issue but I was simply wondering if you had checked to be sure it wasn't partially or fully clogged.......... there are other holes but the engine is tilted slightly and there has to be a lot of oil trapped under the valve cover for it to reach them......

I've seen more than a few with this issue........it's easy to check before digging deeper into the problem...pull the cover off and have a look....

[cleszkie]

Originally Posted by Ryanz

I assume by baffle you mean the rubber piece under the PCV valve - yes it is there and in good condition. Also checked the modulator and it is dry - son of a... Thank you for the suggestions. Looking more and more like it is a ring. Expensive fix for a guy who can't do it himself. (not a mechanic)

The baffle is not rubber. The baffle is made out of stamped steel and is connected to the underside of the valve cover directly under the PCV valve port. The baffle prevents oil from splashing up onto the PCV valve from the rocker arms, and getting sucked into your engine. If you don't have a baffle, then this is at least part of your problem, if not all of it.

When you checked the modulator, did you pull the rubber vacuum line off and check for ATF in the line? If so, you did right. If not, this is what you need to do.

[Ryanz]

Originally Posted by cleszkie

The baffle is not rubber. The baffle is made out of stamped steel and is connected to the underside of the valve cover directly under the PCV valve port. The baffle prevents oil from splashing up onto the PCV valve from the rocker arms, and getting sucked into your engine. If you don't have a baffle, then this is at least part of your problem, if not all of it.

When you checked the modulator, did you pull the rubber vacuum line off and check for ATF in the line? If so, you did right. If not, this is what you need to do.

Yes, checked and modulater is dry and I do have a baffle. Dammit.
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