Motor has greasy white froth build up coming out of block breather.

[Zed Head]

It sounds like the catch can is doing what it's supposed to do. The way you have it set up is like a distillation condenser in a chemistry lab. Moisture vaporizes in the hot engine, the water vapor makes its way to the can and condenses as water in the can. If you wrapped the pipe/hose from the crankcase to keep it hot until it gets to the can, then the sludge would probably only collect in the can.

And I don't think that there's a P in your PCV, since you aren't applying intake system vacuum. It really is just a distillation device for water, from the oil. If you moved the hose from the valve cover to an intake manifold port, and blocked the filter, then the PCV would work like it was designed, I believe. Probably keep your oil cleaner too. Or you might collapse the catch can like a cool science experiment.

[LeonV]

The valve cover pipe goes into the catch can, then theres the PCV hose that goes into the catch can as well. The catch can itself has a vented filter and a drain plug. But since the catch can isn't catching any oil I might vent the PCV to atmosphere.

I don't think you followed my last post. You said you have a PCV valve installed. Since it is not connected to manifold vacuum, the PCV valve is closed and will not let the crankcase vent. If you remove your PCV valve and run a hose directly from the crankcase to the vented catch can, you will be fine.

[LeonV]

It sounds like the catch can is doing what it's supposed to do. The way you have it set up is like a distillation condenser in a chemistry lab. Moisture vaporizes in the hot engine, the water vapor makes its way to the can and condenses as water in the can. If you wrapped the pipe/hose from the crankcase to keep it hot until it gets to the can, then the sludge would probably only collect in the can.

This would possibly be true only if the PCV valve were open.

[Wade Nelson]

Yeah, by that description it sounds like a head gasket or block issue.

What he said.

[Zed Head]

This would possibly be true only if the PCV valve were open.

There are several this's in my post so I'm not sure which "this" you're referring too. PCV valves have a spring inside (I'm sure you know this) that holds the valve partially open (this might be where the different view comes in). It's a normally open valve, restricted at high vacuum or flow rates, closed completely by backfire. So with no flow from pressure differential to close or open the valve the gases will just float through and fill space until they hit the cold can and condense.

I only know this because I had a plugged PCV on my Pathfinder and after removing it and cleaning it up, I had to go to the FSM and the internet to confirm how it was supposed to operate (because I could blow through it both ways). It's a little more sophisticated than it seems, with a two way valve that is designed to move both ways at certain pressures. Purty cool.

[MKI4EVA]

looks like water is getting in somewhere. Seems to have power still but I got a mechanic to look at it and to my surprise creamy oil all in the cam cover. This motor only had about 15,000km on it too......

Motor build time.

Thanks guys.

Edited August 9, 2012 by MKI4EVA

[LeonV]

There are several this's in my post so I'm not sure which "this" you're referring too. PCV valves have a spring inside (I'm sure you know this) that holds the valve partially open (this might be where the different view comes in). It's a normally open valve, restricted at high vacuum or flow rates, closed completely by backfire. So with no flow from pressure differential to close or open the valve the gases will just float through and fill space until they hit the cold can and condense.

I only know this because I had a plugged PCV on my Pathfinder and after removing it and cleaning it up, I had to go to the FSM and the internet to confirm how it was supposed to operate (because I could blow through it both ways). It's a little more sophisticated than it seems, with a two way valve that is designed to move both ways at certain pressures. Purty cool.

I don't know about the Pathfinder, but that's not how the Z PCV system is designed to operate. The spring (we're talking Z's) holds the valve closed. At a certain vacuum, it opens, as determined by the spring constant. The higher the vacuum, the more it opens, hence "variable orifice".

Keeping the vacuum side of the PCV at atmospheric pressure is the same as WOT, no flow. Have you tried blowing through both sides of a Z PCV?

From the '72 240Z FSM:

A variable orifice valve is used to feed crankcase blow-by gas to the intake manifold. During partial-throttle operation of the engine, the intake manifold sucks the blow-by gas through the valve. [...] Under full-throttle condition, the manifold vacuum is insufficient to draw the blow-by flow through the valve, and the flow goes through the sealed system in the reverse direction.

[Zed Head]

The text from the FSM doesn't say that the valve is normally closed. It says that the flow direction changes and shows a drawing of flow coming from the valve cover hose under high blow-by conditions, because the crankcase gets pressurized.

And yes, I did blow through both sides and also noted that the valve plug is held in the middle of its travel range by the spring. I just went out and confirmed on an old PCV valve in the garage. It was from a 1981 ZX though. But I looked at a 78 Z valve also, in the past (one advantage of hoarding). When I was working on it I wondered if the spring tension is tuned by the engineers to allow a certain amount of flow, since different engines have different part numbers (at the auto parts stores) even though the outside form is the same. I ended up putting a Z valve on my Pathfinder just to be contrary. It works fine (by the way, the original reason for even looking at it was milky oil on the filler cap).

Not trying to be argumentative. I was perplexed when I was working on it because I thought that it should be normally closed then open under vacuum. But you can poke both sides of the internal valve plug with a small screwdriver and it is definitely balanced in the middle, at the end of the spring. If you Google PCV valve you'll find a ton of descriptions with illustrations showing low flow at high vacuum and high flow at mid-range vacuum. Closed at backfire.

There's actually a current thread over on Hybridz about the PCV valve on a turbo engine. It seems to be a more complicated part than you would think from its external appearance.

[madkaw]

I'm with Leon, there's no vacuum so the PCV is staying closed. Of all the PCV's I have seen, I have never seen one where it is partially open-but not saying there aren't ones that do operate that way. Most of the ones I have taken off of our cars there was no spring at all, just a free moving ball!

To the OP, why are you ready for a new motor, your not sure what the issue is. Go down to Autozone and borrow there coolant pressure tester and see if you have pressure building in your engine, then go from there.

[madkaw]

The text from the FSM doesn't say that the valve is normally closed. It says that the flow direction changes and shows a drawing of flow coming from the valve cover hose under high blow-by conditions, because the crankcase gets pressurized.

And yes, I did blow through both sides and also noted that the valve plug is held in the middle of its travel range by the spring. I just went out and confirmed on an old PCV valve in the garage. It was from a 1981 ZX though. But I looked at a 78 Z valve also, in the past (one advantage of hoarding). When I was working on it I wondered if the spring tension is tuned by the engineers to allow a certain amount of flow, since different engines have different part numbers (at the auto parts stores) even though the outside form is the same. I ended up putting a Z valve on my Pathfinder just to be contrary. It works fine (by the way, the original reason for even looking at it was milky oil on the filler cap).

Not trying to be argumentative. I was perplexed when I was working on it because I thought that it should be normally closed then open under vacuum. But you can poke both sides of the internal valve plug with a small screwdriver and it is definitely balanced in the middle, at the end of the spring. If you Google PCV valve you'll find a ton of descriptions with illustrations showing low flow at high vacuum and high flow at mid-range vacuum. Closed at backfire.

There's actually a current thread over on Hybridz about the PCV valve on a turbo engine. It seems to be a more complicated part than you would think from its external appearance.

I'm Always learning something on these sites:)

I will note that the early Z's with the balance tube put the PCV in an angle to put the weight of the "ball" towards the closed position-in essance a spring

Edited August 9, 2012 by madkaw

[Zed Head]

If the early PCV valves are just ball-type check valves then gravity is a factor and proper installation comes in to play. I didn't know that the early ones were of that type, maybe that's our difference here.

Back to the OP's problem though, a full engine rebuild due to some milky oil is a sign that someone wants a new engine:classic:. Water is a byproduct of combustion (watch your exhaust pipe when the engine is cold) so, with a little blow-by and many short trips water buildup is still a likely cause of the water in the catch can. A few simple tests would tell the full story.

[beermanpete]

I agree, a rebuild seems unwarranted at the moment. The primary problem seems to be a lack of constant movement of air through the crankcase to remove moisture and other gasses. At this point even a road draft tube would help.