Damn Oil!!

[Scott Larson]

That three dollar part is VERY important indeed! Without it, excess pressure can build in the crankcase and blow oil out through the path of least resistance say, for example, the dipstick tube or the seals. Leaving the crankcase to vent directly to the atmosphere adds to pollution and that is why it is an integral part of the pollution control system. Years ago, it wasn't mandated and therefore didn't exist. The oil filler cap was usually vented and that allowed crankcase pressure to equalize with atmospheric pressure. That little part has been the cause of countless problems and engine failures, I guess that counts as a BIG problem!! When that part clogs, that's when the excess pressure problems begin. Now, the blowby problem is not a pcv valve problem, but it causes pcv problems; namely a clogged valve or messy residue within the intake system. That blowby is caused by excessive compression leakdown past the pistons compression rings allowing oil on the cyclinder walls typically controlled by the wiper rings to be blown into the crankcase as an air/oil mist. That mist is then expelled out of the pcv system through the pcv valve!

Hope that helps explain things a bit better...

[PK]

PK, explain this again.....
"So, it is possible to have excessive blowby without being an oil burner, and vice-versa."

Well, this is my understanding of how piston rings work, but I am not specifically a trained mechanic.

The top ring is solid in cross section, and slides hard against the cylinder wall. It has the primary function of keeping the combustion gasses and compression, in the combustion chamber. Excessive blowby occurs if this ring, or the cylinder walls, are worn or scratched. Also, if the ring groove in the piston is worn, the ring can stick so that it is not hard against the cylinder wall.

The bottom ring has special contours in cross section. Its prime function is to take most of the oil (not all) off of the cylinder walls. This oil is thrown up by splashing of the crankshaft etc as it rotates, and also from the oily mist that is always in the sump when an engine is operating. This ring actually guides some of the oil back into the ring groove and back to sump through drain holes in the piston skirt. That is why there has been some talk about the piston drain holes being responsible for the VX burning oil. If the drain holes clog up, or the ring wears or sticks, you have an oil burner.

The middle ring helps restrict any blowby that gets past the top ring, and any oil that gets past the bottom ring. It also covers the "gap" area in the top and bottom rings. But it is not 100% efficient in either role, so if the other rings are worn, some of the excess still gets past.

Depending on what is worn and how much, you can have an oil burner that still has good compression and no blowby. You can also have excessive blowby and not be a large consumer of oil.
However, the normal would be for relatively even wear, and you have both blowby and oil burning.

Note that the rings are never 100% efficient.
If the oil rings took every little bit of oil off the cylinder walls, the top ring would wear very quickly, so a small film of oil is always there to lubricate the top ring.
This is what is considered "normal" oil consumption, and different manufacturers will rate their engines differently.


Now, you guys have to decide if I have blinded you with science, or baffled you with bull scat??

PK

[Scott Larson]

Blinded with science PK, you nailed it!! It's controlling that pesky oil mist that seems to elude the average VX...

[Monstertrucker]

Is there anything else that could be causing raised crankcase pressure causing massive amount of oil to be pushed up into intake? Any thoughts??

Unless they've recently been replaced, your fundamental problem is probably more basic, i.e. worn out exhaust valve stem seals (and to some extent intakes as well but only if they're very badly worn).

With worn stem seals, excess oil runs down the valve stems into the combustion chambers, which is then burnt at startup making it smoke blue for a few seconds until it burns off. However, the exhaust gas (and excess oil) is also forced out of the top of the valve stem seals (under the spring retainers) and directly into the rocker/valve covers at high pressure, coating everything with said oily crud and carbon, (burnt oil).

Does it smoke blue on startup and at high revs? If not, either

A) I don't believe you.

B) Ignore me and check your plumbing or whatever they said.

[Monstertrucker]

Positive Crankcase Ventilation is exactly that, it allows for the ever-changing volume of air in the crankcase to be expelled and subequently replaced as the volume changes due to the reciprocating pistons in their bores.

Not quite; it's thermal and gaseous expansion that we're concerned with since the crankcase pressure doesn't change due to mechanical movement; piston ring and stem seal blowby notwithstanding, of course.

As a pair of pistons go up, a pair go down so it's a static volume in that regard.

[Ebenezr]

You all hit the nail on the head and this picture shows the inside of the common chamber (intake) bathed in oil mist from excessively blowby. My compression had sunk to 120 +- on all cylinders. Mfg specs say the minimum should not be less than 145! and feel this is where my HP loss was coming from. So I traded my VX.

[Ebenezr]

X a factor of 2...

I've gutted my PCV system, & it now flows freely into a catch can, which is vented into the air box, with zero reduction in oil consumption.

This is an interesting idea Dub. I thoughtof running my pcv down into a canning jar with some kind of filter and then back out again to the intake. I dea being the oil would be filtered out and fill the jar.

[Monstertrucker]

Compression loss is usually due to poorly seating valves. As with the stem seals, it's the exhaust's that wear the most because of the heat that they're subjected to.

If you just have the heads rebuilt, (all gaskets and stem seals replaced and a fresh valve grind/hone), you'd be back to good as new.

Piston rings are the last thing that will cause poor compression, given the beating that the valvetrain gets and the size of the components/sealing materials used.

[Ldub]

This is an interesting idea Dub. I thoughtof running my pcv down into a canning jar with some kind of filter and then back out again to the intake. I dea being the oil would be filtered out and fill the jar.

That's what I thought too...

The strange thing is, there is plenty of evidence that there is oil being forced from the valve covers. There is always an accumulation inside the air filter box.
But I've never seen any accumulation in the catch can....

It's either travelling so fast as a mist, that it goes right through the can, or something came loose inside the can, or I need to add more steel wool as a baffle.

Gonna have to look into it come spring...

Lastly...find yourself a nice aluminium container...I think that a glass jar would be kinda sketchy under the hood.

[Scott Larson]

Not quite; it's thermal and gaseous expansion that we're concerned with since the crankcase pressure doesn't change due to mechanical movement; piston ring and stem seal blowby notwithstanding, of course.

As a pair of pistons go up, a pair go down so it's a static volume in that regard.

Staggered timing negates your theory...no difference between one cylinder or sixteen, sorry!

[Scott Larson]

You all hit the nail on the head and this picture shows the inside of the common chamber (intake) bathed in oil mist from excessively blowby. My compression had sunk to 120 +- on all cylinders. Mfg specs say the minimum should not be less than 145! and feel this is where my HP loss was coming from. So I traded my VX.

Now THAT is some serious blowby!!! No wonder you decided to trade it in...$$$

[Ldub]

Now THAT is some serious blowby!!! No wonder you decided to trade it in...$$$

At least the butterflies & their associated control shafts were staying well lubricated...

[Ebenezr]

Compression loss is usually due to poorly seating valves. As with the stem seals, it's the exhaust's that wear the most because of the heat that they're subjected to.

If you just have the heads rebuilt, (all gaskets and stem seals replaced and a fresh valve grind/hone), you'd be back to good as new.

Piston rings are the last thing that will cause poor compression, given the beating that the valvetrain gets and the size of the components/sealing materials used.

I almost pulled my heads to do a valve job but my mechanic had a method of pumping compressed air into the cylinders with the valves closed. He said if the valves were leaky then there would be an audible hiss. In my case he decided worn rings was the culprit. Years ago it was sort of a risk to do valves and not the rings as well because the firmly seating valves increased compression and worn rings allowed "more" blowby. Therefore doing a valve job only kinda didn't work well.

[p_justin13]

Ran sea foam in crankcase for about a hundred miles then changed oil and ran 1/3 a bottle through the pcv with engine at idle drove for a day about another hundred miles and ran another 1/3 of a bottle through the pcv again. Idle and acceleration is much smoother. Still getting strong smell oil in exhaust when i gun the throttle. Also does anyone else vx rev really high on startup. Like 1500-2000 rpm for a minute or so then goes back down to normal 700-900. I still have to replace manifold gaskets. Not really leaking yet but around that time. Scared to see what I find when I do.