My 383 has about 2,000 miles on it and I've been running a PCV valve since day one. I noticed that if I go on a highway trip, oil comes out of the breather on the opposite valve cover (The breather has a Moroso baffled gromet). In-town driving does not seem to have this effect.

I have verified that the PCV system has suction by removing the open breather and testing with a vacuum gauge (have about 3-5 in vac @ idle). I have about 11" engine vac at idle and I would estimate about 16 or so at highway speed (OD trans, 3:42 rear - turns 2K RPM at 70 where I cruise).

Seems odd that oil would come out of the breather with so much vacuum pulling the oposite direction (unless something odd happens at highway speed with the PCV valve).

I figured that I had a blow-by problem and checked compression first and came up with 205 - 210 psi. Then used a leakdown tester and unfortunately have yet to figure out a percent leakage yet but according to the gauge all was "normal" (the book that came with it says that % leakdown is not displayed but the gauge itself says % leakage - trying to contact the manufacturer). I did have one cylinder that had about 2.5 xs the leakdown than all the others but again, I don't know what this means other than the gauge said "normal".

If this one cylinder does have a ring seal problem, would this be enough to cause the problem I have? Do I need a "higher capacity" (if there is such a thing) PCV valve?

Any ideas?

If your PCV valve is working correctly and you have baffles in your valve covers under the the fill cap, then you have ring problems. God knows I've been dealing with this too lately.

I've heard many of the aftermarket PCV vales are "one size fits all" where the factory had many different ones. Maybe try a GM PCV valve?

Next, what kind of valve covers? Stock seems to control oil the best. I haven't seen any aftermarket covers with baffles as good as GM.

Finally, there is no way to prevent some oil mist coming out at high load or WOT. How much depends on leakdown. That's why the factory routed the fresh air side to the air cleaner so the mist would be sucked into the engine. Could you be seeing this and thinking it's from highway driving when it was really puked at high load?

/Markus

I am running old cast aluminum M/T valve covers that came without breathers.

"Finally, there is no way to prevent some oil mist coming out at high load or WOT. How much depends on leakdown. That's why the factory routed the fresh air side to the air cleaner so the mist would be sucked into the engine. Could you be seeing this and thinking it's from highway driving when it was really puked at high load?

I made a trip from NC to FL and really was easy on the car. The engine never spun higher than about 3,500 RPM the whole trip and that happened once or twice. No full throttle at all.

I am running old cast aluminum M/T valve covers that came without breathers.

So there are no baffles inside the covers? That would be the problem then.

Edit: Re-read the OP and you state you have a moroso baffled grommet. I've seen these and although I haven't tried one it doesn't look to me like it would do much good compared to a proper baffle.

Yeah zwede, I have found that those Moroso "baffled" grommets just plain suck. I have the same problem right now with my valve covers. I am just going to replace them with a set of baffled covers.

Yeah zwede, I have found that those Moroso "baffled" grommets just plain suck. I have the same problem right now with my valve covers. I am just going to replace them with a set of baffled covers.

They are worthless on the PCV side but I am using one on the breather side. The PCV side has a home-made baffle that took some trial and error to get it right and I do not have a problem with that at all.

Again the issue is that at idle, I have suction through the breather - so alll works good. But at cruise speeds, oil comes out of the breather.

I may just install one of those header evac systems