What should I do next?
 

So I have a 78 Corvette and it burns a substantial amount of oil (1qt every 100 miles) I have been trying to figure out what is causing it to burn all this oil. I did a compression test and got 190 psi in all the pistons so I figured it was valves seals cause the only time I see any smoke is on start up. I replaced the pcv valve cause it was cheap and was worth a shot and that didn't help. So today I was going to try and adjust the fuel mixture because the exhaust fumes are horrible and I figured it was running rich but when I went to adjust the mixture based on vacuum the that gauge was jumping around from 12 to 17 in hg very quickly while at idle. I looked this problem up and got a bunch of different problems it could be. They all seemed to be ignition related or valve train related. So I was hoping someone would know a good time next step I don't have the money to start just replacing parts I really want to try and pin point the problem before spending a ton of money on new parts I don't need.

Tell us about your valvecovers. Aftermarket? Do they have a baffle to block excessive oil mist from being sucked into the PCV?

Was the intake manifold changed recently? A poor seal with the gasket bottom side can introduce oil from the lifter valley.

And for what its worth. You can have good compression test in all cylinders but still have oil ring failure.

With the only information of a jumping vacuum test, using oil and just replaced valve seals, it seems you may have worn valve guides.

https://dannysengineportal.com/how-to-do-a-vacuum-test/

You said it smokes at startup. Assuming this is blue smoke, it points to valve seals or valve guides again.

If it is black smoke at start up, that is fuel and may need to be leaned out a bit. This does not solve the oil use issue obviously.

It's likely the intake manifold sucking it in from the lifter galley. Pull the manifold, clean all the surfaces, while protecting the engine internals from getting a pile of gasket crap on it, then clean the edges on both intake and engine with lacquer thinner, MEK, or something that will get rid of oil residue.
Once that's done, reinstall the manifold using new gaskets. Don't use the gaskets on the end walls (china walls), just use a bead of RTV sealant thick enough to seal all the way along. let it sit overnight to cure before starting.

I would recommend "The Right Stuff" by Permatex instead of RTV. RTV works just fine, but this stuff is more wonderful and works fast. You can't be lollygagging.

https://www.permatex.com/products/ga...e-gasket-grey/

After using it the last time I did a top end rebuild, I would not use RTV unless I was in a bind and had run out of this stuff. More expensive, but I think it is well worth it.

I always put a dab of sealant on the intake bolt threads also. Can't remember which ones, maybe the 4 center bolts,thread all the way into the oil gallery. I dab them all just in case.

Dr1rrr

Unfortunately there is not a test you can conduct to verify the intake manifold gasket is leaking. And its not real common but does happen due to getting in a hurry during installation. Or using the wrong sealing product. carriljc is right-on about Permatex Right Stuff. Best on the market, hands down.

Spraying carb cleaner on the intakes gasket while engine is running only verifies vacuum leaks on the upper side. It verifies nothing for the bottom side of the gasket in the oil flooded lifter valley.

I really doubt your oil consumption is valvestem seals. Even with no seals in place, your engine would never drink a quart of oil in 100 miles. That's beyond excessive.
That leaves the rings. Could be, but doubtful. I also believe that out of that one Qt per 100mi, some is dripping on the floor also.

What is the history on the intake manifold? Just swapped out recently? Original?

I am going to say it is the intake as well......sucking from underneath. This would cause heavy oil consumption, stinky exhaust, and a bouncy vacuum needle.
R&R the intake or install an upgrade one while the old one is off......like the 2101 Performer. This can give you a chance to also use the 1204 Fel-Pro intake gasket that blocks off the heat riser.....which will lower carb temps.

Jebby

Put a smoke machine in the pvc hose carb side take off the oil fill cap and watch for smoke , if the intake gasket is leaking from underneath it might let smoke in the lifter galley then up in the valve cover.... or you can pump the smoke in the valve cover and see if smoke comes out of the carb ... its worth a try not a lot of work.

My valve covers are the stock l82 valve covers and the engine was rebuild a few years ago is what I was told by the previous owner along with a few other things that were replaced but everything that was done to the car has been done wrong and I've had to redo

:iagree:

I also think it's the manifold, have you checked to see if the manifold bolts are torqued tight ?

i glue the gasket to the heads with a small amount of RTV. Use the rubber end pieces as they have locators for the gaskets. drop manifold on with no sealer on top of gasket to press it down. when cured, pull manifold and check location and adhesion of the gaskets below intake ports. now you know gasket is in the right place and gonna stay there. replace rubber ends with RTV or not your choice.

When removing intake, you are looking for signs of oil getting into the intake ports. if you don't see any, the gasket most likely wasn't the problem and you need to move on to the valve seals.

How I checked was to scribe a line through the centerline of the bolt holes of the head, intake and intake gasket. From there its easy to dry align the parts and check for proper overlap.

Just got a set of gaskets today and I'm going to take it apart this weekend hopefully to try and see what's up with it thank you guys for all the replies I will post what I find out

Take some pics along the way and post them up!!

Sorry for the delay guys but I finally got sometime today to take the intake off. I found some strange stuff along the way. so the first weird thing was when I went to unscrew the intake bolts some of them were just finger tight, about half were tight half were not. The other weird thing is that the gasket had not seemed to have moved or shifted any so I pulled one of the gaskets off a little to check behind it and found a lot of oil between the gasket and the head. Also there was a lot of built up dirt on the cylinder head where the intake did not cover and a lot of oil in the intake runners. I would say this oil could have been leaking from the valve cover but it didn't have any of the other symptoms of a leaky valve cover. Here are some pics I took in the on with my finger that was wiped from right in the middle of where the gasket sits. Tell me what you guys think.
https://cimg1.ibsrv.net/gimg/www.cor...3b8df13a94.jpg
https://cimg5.ibsrv.net/gimg/www.cor...c57a09b36e.jpg
https://cimg9.ibsrv.net/gimg/www.cor...784bc56f83.jpg
https://cimg0.ibsrv.net/gimg/www.cor...cd3d0218aa.jpg
https://cimg3.ibsrv.net/gimg/www.cor...ffc6881fb0.jpg
https://cimg2.ibsrv.net/gimg/www.cor...b30620b145.jpg
https://cimg4.ibsrv.net/gimg/www.cor...de6da3bc2d.jpg
https://cimg6.ibsrv.net/gimg/www.cor...0830a89db3.jpg
https://cimg7.ibsrv.net/gimg/www.cor...6d7fccd292.jpg
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No doubt, your oil consumption was from the lifter valley. So, shove paper towels into the cyl head ports. Start scraping the head with a plastic putty knife or there are some pretty slick plastic razor blades on eBay. Either one will not scratch the cyl head. When you think you got it clean, wipe it down with Acetone. Then do the china walls.

Go to Summit and search Gaskets>Intake>FelPro. I do not know what size ports you have, nor which part number you need. You will also need Edelbrock Gastinich gasket sealer and a small can of The Right Stuff for the china walls. DO NOT use the rubber gasket provided, pitch those worthless things. And new valve cover gaskets.

This is a great time to decide if you need new intake bolts also. Those bolts should receive a dab of thread sealer.

I see your rockers have adequate oil circulation. Valley looks good. Normal wear on the pushrod / guide plates. You should be good-to-go.
I think you will see a huge reduction in oil usage.

Leaking Intake Gaskets ... bolts loose

regular steel single edge blades and/or good penknife fine on those tough iron heads & china rail ... use a bit more care on aluminum manifold.

If you're Not subject to NCRS judging ... and have time to get em ... a set of new intake bolts in the "reduced head size with 12-point" version makes it a lot easier to get to & tighten them ... a dab of permatex #2 or rtv on threads helps prevent oil creep. Don't use stainless bolts.