Is it common for the 390 and 429's to burn oil? Because just the other day while driving my 64, I notice upon start up the same lifter that was making noise a month ago, came back. So I decided to check the oil, and to my surprise there was no oil registered on the dipstick!!

I don't know how that is possible when I don't drive the car a whole lot and the car doesn't smoke, or really leak any oil. Thank god my instincts to check the oil came to light as I was down 2 1/2 quarts of it! 

After adding oil, the oil finally registered on the dipstick and once started up the lifter tap was gone.

I added a couple of gallons of 110 Leaded Octane race fuel in the tank, and took the car for a drive. The engine smoothed out so much that It really help in the idling department with the race gas. Well after 20 minutes of driving, all of sudden while at a stop light, the lifter tap came back, and the engine idled roughly. As I accelerated, I noticed a lack of power, and the tapping getting worse. 

So I pull into the nearest gas station, and suddenly the engine smoothed out and idled fine again. So I quickly drove home and the engine ran great, well as I pull into to park, the tapping came back and yet again the engine idled rough and was sorta shaking. 

I can't understand why this only happens after driving the car for say 20 minutes, and the tapping comes and goes. My first thought is low oil pressure, but the light has never came on. Or a clogged oil pick up screen starving the lifters of oil. I've used 10w40 and 20w50 oil just in case the pressure drops or is low.

The big concern that is shocking to me, is the high amount loss of oil. To lose almost 3 quarts is crazy. Someone told me to stay away from Synthetic as I used 0w40 Mobil 1 when I did the oil change a couple of months back, and stick to high mileage dino oil, or just use conventional oil. One of my co-workers owns a 70 Chevy pickup with a 350, and he was using full Syn oil at one point in time, but it leaked out badly from the seals. So he started using diesel oil, specifically Delvac, and the leaking stopped completely.

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These motors should not use oil. Its a closed oiling system, that recovers the oil in the pan, to be recirculated through the engine.

Your loosing oil through combustion, leaks, or blow by out the fill tube.

It sounds like you have 2 separate issues with the engine.  Oil loss, and intermittent rough idle.

Ok that was my concern, I'll just have to keep an eye on the level, and maybe just using conventional oil and see if that helps to keep the oil loss down. I'm going to get under the car and inspect to see if there's any sneaky leaks that I might not be noticing.

If you are not leaking or smoking ,it is very hard to understand your oil loss
You do need to check your oil more often
Have you lost any oil since your last fill up ?

I just filled it up a couple of days ago, so I won't know until a few drives from now.

A mechanic told me that these engines tend to leak out at rear main seal while driving, but wont leak while it is parked.

Cadillac was in the forefront of technology, so these engines weren't crude in any way.  They are excellent engines that need top notch maintenance by skilled mechanics.

If your rear main is leaking, just push a new seal in, and do it correctly, otherwise you will have a drip at the new seal.

I've always known that Cadillac was ahead of the game as far as engineering and innovation goes in the 60's, and for them to lighten up an engine like the 429's, yet still have the durability and reliability of a heavier engine is very impressive, including the power they create,

I have to get under the car this weekend and look over any possible leaks closely.Since it can't be burning oil as there is no smoke at all coming from the tail pipe. I remember when I replaced the valve cover gaskets, the rockers looked clean, no sludge or varnish what's so ever,

If your rear main seal is leaking ,you will be seeing some oil on the ground
I would almost feel better if you told me ,you are seeing some oil below the engine in this case
Oil just does not disappear
The valve covers ,on these cars can be a bit tricky to to install,and can leak for that same reason , but you would see oil on the ground ,if that was the problem
Any smell of oil burning off , under the hood
You would be smelling ,an oily vapor ,if valve cover is leaking oil on to the exhaust manifold and evapoating into the air

You know what I think I might of found the problem! The passenger side valve cover I noticed way in the back has some oil seeping out from the edges. When I tightened the valve cover bolts, they were a little loose.

A few months ago I replaced the valve cover gaskets and repainted the covers. I obviously didn't tighten the bolts down hard enough.

I hope this was the problem all along as I really don't see any leaks on the ground besides for the oil drain plug sometimes will drip slightly. If so, It's hard to imagine losing that much oil when I don't drive the car a whole lot. But you never know.

Chris, you may need to replace the gasket on the valve cover.  Its easy to overtighten the bolts, and squish the gasket out of shape.  

Use a good gasket sealer when installing the gasket, so its a double whammy to stop oil leaks.

Russ, I used cement glue to hold the gasket in place which works wonders. Gasket sealer can work, but I noticed it doesn't have the strength to keep the gasket in place in areas where you can easily bump the part up against something. Just a small nudge can knock the gasket out of place or will remove it all the way the times where I had to replace gaskets.

If the leak continues, I'll probably add some sealer around the lip where it is leaking.

Check the lip of the valve cover. They often get warped downward around the 4 bolts. If warped take two good boards with nice square edge and cut one to length to go under the lower ride and another over the top, and take a large 2 1/2 to 5 lb club hammer and whack it until straight on both sides. I've almost always had to do this anytime I am reconditioning valve covers. Keep in mind that per factory spec the torque is 28 inch lb which is only 2 1/3 ft lb.  People put brute force on these and end up bending that lip down and will not matter which type valve cover gasket you use, as it will still leak once been too far down. As for gaskets, I tend to like the very tick cork/rubber filled gaskets. Also be sure to use the original elongated washers under the 3/8" hex head bolts, or the aftermarket type hold down washers that spreads the weight. If you need the original bolts, washers, or valve cover gaskets shoot me an email to jasonedge@nc.rr.com  

 

You know Jay, my very good neighbor mechanic friend actually made sure the covers were flat as can be, because like you said, they were warped when I removed them and he hammered out the spots that weren't even. He was able to fix the warpage, so I am guessing the bolts weren't tightened down enough, but I need to drive the car  first to see if the leak stops completely.

If the leak doesn't stop, I will just have to remove it and fix it once and for all. BTW I used the Cork gasket, as it is very thick and cement glue to keep the gasket in place before I installed it.

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