390 still using oil

[shady]

Do you think it is slowly getting better or worse? What kind of rings did you use and what kind of oil do you use? All the plugs look the same?

[blykins]

This engine has been completely worked including the heads and guides and everything else. Could it still be the guides? Also if the intake gasket was leaking would a vacuum gauge not show it?

Probably not. 

What do the plugs look like?  Have you looked at all 8?

[wayne]

The last thing to try if you cant find it get some bon ami cleaner and pour it down the carb when its running the rings will seat this was done by gm to fix the 55 265 and later the 327 look it up it works.I have seen it done

[390owner]

I think it is getting a little better. It is not using as much as it was at first. The plugs all look the same and are clean.

[gdaddy01]

I hope it goes well for you .

[shady]

I'd keep running it.

[67428GT500]

my guess is the rings never seated. Put some Rislone in it and drive it like you stole it. You don't need to over rev it, but I'd punish that bad girl.

Which Rislone are you recommending for new engines that didn't seal? There seem to be quite a few. One is synthetic. Brent and a couple others suggested staying away from synthetics on new builds. Or is the small quantity safe?

[wowens]

The last thing to try if you cant find it get some bon ami cleaner and pour it down the carb when its running the rings will seat this was done by gm to fix the 55 265 and later the 327 look it up it works.I have seen it done

It's been since about 1970 since I've thought of this. I personally know of it being done on a FE, seemed to work for a while, then lost can bearings.

[machoneman]

my guess is the rings never seated. Put some Rislone in it and drive it like you stole it. You don't need to over rev it, but I'd punish that bad girl.

Which Rislone are you recommending for new engines that didn't seal? There seem to be quite a few. One is synthetic. Brent and a couple others suggested staying away from synthetics on new builds. Or is the small quantity safe?

Rislone Engine Treatment.  Available at most auto parts places.  It has a good quality engine oil as its base, plus effective solvents to break up sludge, varnish, and piston ring deposits.  I've had good luck with it and you won't hurt anything.

https://shop.advanceautoparts.com/p/rislone-engine-oil-treatment-32-oz-100qr/7081049-P

[390owner]

ok a update on the oil consuming on  new 390. If I rev it to 3000  the let off and give it gas again it puffs smoke every time Blue smoke Still sound like the rings?

[machoneman]

Maybe. But we still have not seen either a compression test nor leakdown test. It is possible btw both may look pretty good if the oil rings/expanders are stuck. Easy stuff to check too is if the vavle seals are still good, the guide-to-valve clearances are not excessive (a bit harder to diagnose) and one is sure no intake gasket leaks nor PCV valve issues are the cause of the smoke.

[Keith M]

I had something similar in my 67 F250 with 390 & NP435.  Taking off, wouldnt smoke, shifted below 2500-3000 it wouldnt smoke either, but higher and it would.  Thought maybe too much oil up top sucking it out the pvc, so I restricted the oil coming up top.  That wasnt it.  Thought valve guide seals, they were a bit hard, but still pliable and all 16 were whole, still replaced with alex's parts positive seal (the ones for factory sized guides).  Same problem.  Just kept driving the truck as it was my only means, so I would just short shift.  Then it started to get worse, it would start to smoke on shifts no matter the RPM, but it was erratic.  Then once in a while, it would throw a bunch of smoke out of the exhaust when I would take off from a stop, I could tell it was going to do it as it would just slightly start to run rough right before it did it.  It was embarrassing to me as it would leave this huge smoke ball that would just linger.  Finally took the valve covers off and it was the intake gasket.  The #3 & #6 intake gasket separated near the top.  Weirdest thing I ever saw.  Fixed it, still smoked a bit, but after a couple months, no smoke.  Like they said before, some residual oil I figure in the exhaust.  In the one picture, you can see the #6 gasket sticking up slightly.

This truck has C6AE-U heads and CJ intake. 

Keith

[390owner]

I am going to put a vacuum gauge on it again and see what it says. Like mentioned before this engine  a year ago had all new parts put into it by a machine shop that has been in business for over30 years. I am sure the guides and seals are still good from the build. I will try to get a compression test done also. If the intake seal was bad shouldent the vacuum gauge show it??

[My427stang]

Vacuum gauge rarely shows a vacuum leak like that. 

To me, it absolutely doesn't sound like rings.  It sounds like oil being pulled by the guides or the bottom of the intake, or into the PCV.  Why?  could be many reasons

1 - Crappy valve seals
2 - Blocked returns
3 - Loose guides
4 - No seals on the exhaust, old school not the greatest idea IMHO
5 - Poor gasket seal on the bottom of the intake
6 - Bad design for the valve cover baffle allowing oil to be sucked in

Questions
What is your intake/head combo and what did you use for intake gaskets?
What did you use for valve seals?

[machoneman]

Yes, it's possible but not likely a vac. gauge could show a leaking intake gasket. But only if it's a somewhat massive leak.

But, you've not posted from what I can see what you idle vac. numbers are.

As pointed out in other posts....My427Stang even listed possible causes noted below:   
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Vacuum gauge rarely shows a vacuum leak like that.

To me, it absolutely doesn't sound like rings.  It sounds like oil being pulled by the guides or the bottom of the intake, or into the PCV.  Why? Could be many reasons

1 - Crappy valve seals
2 - Blocked returns
3 - Loose guides
4 - No seals on the exhaust, old school not the greatest idea IMHO
5 - Poor gasket seal on the bottom of the intake
6 - Bad design for the valve cover baffle allowing oil to be sucked in

Questions
What is your intake/head combo and what did you use for intake gaskets?
What did you use for valve seals?

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

You could pull the intake and carefully inspect the lower edges (valley side) of the gaskets to see if they have uniform crush all around each 8 intake runners. That and the overall condition of the gaskets. Then, you could use a valve spring puller to remove a few at random and check if the seals are intact, tight and not damaged. Or, take off the heads and have a shop check the guides, seals, etc.

Short of some teardown and close inspection, you'll either need to live with the smoke or dig into it.