I have an engine that loves to consume oil on the highway. I can drive about fifty miles and suck down 1/8th of a quart. On the street though, at low speed, it consumes hardly anything. I can see smoke in the rearview mirror only if I wind it up to 80 mph and then let off the gas and coast. Otherwise, during cruising, I can't see a thing.

Compression is good. 160 - 165 PSI. Idles smoothly. The valve guides were checked on the heads about a year ago. All checked out. I installed new seals anyways. Heads are AFR 180cc.

I am running a PCV and one breather. The covers have baffles.

The rings have about 2000 miles on them. They should be seated now, shouldn't they? They're regular quick-seaters.

No oil on the plugs either.

I'm running 40 weight oil for the hot weather, though the engine was broken in last winter with 30 weight oil. I live in California.

I suspect that it is the PCV, because when I take it out of the covers, a few drops of oil come out of it, and the inside of the hose has oil in it. The intake also hase a fine coating of oil on it. Thing is, I have tried replacing the PCV numerous times, and nothing has changed.

I did buy a new GM valve (the kind with no moving parts) that is supposed to fix the problem, but that is still in the mail.

I just want to make sure I'm not overlooking anything. Any ideas?

If it consumes oil and only shows it under decelleration, most likely it's valve guides.

With the PCV removed from the valve cover and the engine warm and idling, is there air pressure or mist coming from the crankcase? (PCV hole in the V/C) If so, that can be a sign that the rings haven't seated yet. You could also be drawing oil through the PCV if the cover isn't baffled well enough. You could also be drawing oil between the intake and heads at the bottom of the ports if the gaskets aren't doing their job. (cracked gasket, alignment issue, intake geometry doesn't match the heads, gaskets don't have sufficient compression, etc.)

The PCV is to allow the gasses from inside the crankcase to be pulled into the intake. If the baffling is insufficient it can pull oil that is flying around inside the valvecover. Oil in the PCV hose is not a valve problem.

My problem with it being the valve guides is that if I let the car sit overnight and start it up the next morning, I get no smoke from the exhaust. Even if I let it sit all weekend, I don't get the telltale puff of smoke.

I also think that by making the change to 40 weight oil, the consumption would have slowed down some. It hasn't at all. If the guides are worn enough so that making a switch to 40 weight makes no difference, that would have to be a pretty worn set of guides, right? I should expect to be seeing a huge cloud of smoke while cruising at 70 as well. Fact is that I am not.

I am getting a fine mist coming from the PCV grommet when I remove it. It's not heavy though. I get the same amout from my '88 Suburban, which doesn't consume any oil and has good compression.

Are your intake rocker studs open tapped into the intake runners, like TFS heads?

ZS10, no they're not. I checked for this when I was installing the studs when I put the engine together. None are tapped into the intake runner.

GetMore is correct.

Had a comparable problem and it was because the valve covers did not have adequate baffling and were being squirted on by the rocker hole. Use a breather, one with a hose bung for the PCV hose if possible. See if the breather filter gets oily. Mine did.

And does it smoke on the highway? 1/8qt in 50 miles should show some burn-off.

No smoke visible in the rearview while cruising on the highway.

The baffles are OEM style, so I don't see why they should be having this problem.

What do you mean by a PCV with a hose bung?

if you think your pcv is sucking oil back into the engine try using this from jegs .this is much like a air/oil seperator for air tools and will only allow air or in this case vacum re-enter the intake manifold


http://www.jegs.com/images/photos/55552205.jpg

No smoke visible in the rearview while cruising on the highway.

The baffles are OEM style, so I don't see why they should be having this problem.

What do you mean by a PCV with a hose bung?

A closed breather with a hose connection I should have said.
Like when you run a hose from a sealed breather to your collector to help seal rings and evacuate the crankcase.

A hose drooping down low before entering the manifold would be a simple test. If there is a lot of accumulated oil in the hose, there's the problem.

Floor it on the highway and see if it oil smokes.

Ahhh! I see what you mean now. Good idea. That's a nice trick.

Ok. Replaced the PCV with the new one, and the problem seems to have been helped a little, but not entirely.

I had my mom follow me around, and she said it only smokes when I accelerate. I'm guessing this is not bad guides or seals on the valves. This sounds to me like the rings have yet to seat. Am I right?

What year?

Its not 100% common but kinda for the last 70s early 80s GM V8s to get leaks in the lower port of the intake and it will suck oil sometimes.

also one of my projects, been in same circles, thought it was a bad tran mod, then thought PVC............ Same kind of thing only if your real hard on it does it blow smoke sometimes. Had to find a real old engine guru to get a handle on that one. All makes sense when I learned that bit of info.

Not sure if its a true defect but some how they can not seal 100% on the lower part of the port. Im gonna get a new gasket n use indian head gasket crap on it to make sure it never happens again. I assum it just an age n time thing n there is less hold pressure in that one spot n so its goop time baby.

Ended up going to autolite platinum plugs too to stop oil fouling regular AC ones. [they just self clean better] Like ever so often my #6 would go bad and Id get an annoying miss fire at low speeds. as it sucks the wose when it does it.

you could be sucking oil into the intake from a bad intake manifold gasket ,i've seen this happen before and is easily fixed