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You really need a manometer to test it properly because the correct vacuum level is ~5 inches of water, which will never register by your vacuum gauge that measures inches of mercury. 7" of water is already too high.
AFAIK there are no bench tests for the AOS vapor ports anyone has posted here. I think the reason is you will need to simulate the vapor pressure and flow in the crankcase. If you remember how a regular pcv works, the flow is pressure dependent. You can test the two small coolant ports for leak.
Be aware if you have removed vacuum from the crankcase the engine oil accumulate water at an impressive rate. Unburned fuel too. This can be dangerous. If fuel builds up in the crankcase oil it can form an explosive mixture and if it ignites... Say goodbye to some engine seals.
While this is true, the conditions needed to get an explosion in the crankcase is very remote. There's very low stoichiometric ratio inside the engine as it runs. So, the mixture is very far from ideal to ignite, plus one would need a source of ignition inside the crankcase, and that's also very remote. It has happened, but even with a broken AOS the conditions for an explosion is quite remote.
Having said that(we rarely hear of an engine exploding), the AOS is really mis-named. It doesn't actually separate the air and OIL vapor, but separates the air and liquid products, only one part of which is oil vapor. The majority of crankcase vapor emissions are partially burned fuel(products of combustion), slight amount of unburned fuel, water vapor, and a mix of light HC chains.
The water vapor is more of an issue in cars with short drive cycles, because the condensate tends to stay inside the engine, and is not flushed out with a long, warm drive where the temp in the crankcase gets above ~180F. The products of combustion left over in the crankcase are fed back into the intake in an attempt to burn them again. It's a vicious cycle that is circulating the vapor through the engine, then accumulating more vapor, and shipping it back to the intake.
The air OIL separator should be called the air/fluid separator. I have one on my airplane and it's a mixed blessing. It does cut down on some crud coming out of the engine, but the alternative is that some of the products of combustion remain in the oil until they are evaporated out. Most airplanes have longer use cycles than cars, so it's not a problem. The best cure is to take a long drive, and insure the engine gets up to operating temp for at least 30+ minutes. Or, never drive at all! heheh
You really need a manometer to test it properly because the correct vacuum level is ~5 inches of water, which will never register by your vacuum gauge that measures inches of mercury. 7" of water is already too high.
AFAIK there are no bench tests for the AOS vapor ports anyone has posted here. I think the reason is you will need to simulate the vapor pressure and flow in the crankcase. If you remember how a regular pcv works, the flow is pressure dependent. You can test the two small coolant ports for leak.
Ahsai, is the same vacuum present at the dipstick tube as the oil filler cap? I'm assuming yes, but wanted confirmation from someone familiar with inside...
If so, I'm going to make a silicone plug for one of the manometer lines...
Ahsai, is the same vacuum present at the dipstick tube as the oil filler cap? I'm assuming yes, but wanted confirmation from someone familiar with inside...
If so, I'm going to make a silicone plug for one of the manometer lines...
Schnell, I would think so but I never tried. The only other opening on that metal dipstick tube is at where it dips into the engine oil. When the engine is not turning, that opening will be completely submerged in the oil so it's not connected to the crankcase. However, when the engine is turning, the oil level is lowered so that opening should be exposed to the crankcase. Still, that opening may see oil splashing on it.
I think using a used oil cap is easy enough for me so I never bothered to try the dipstick tube. Let us know what you find.
Hey there. I'm waiting for my manometer to get here. Will be here tomorrow. In the meantime, Im curious how this AOS works, just for curiosity's sake.
I also picked up my new AOS today. Its part number is 996.107.026.51
I've been examining it, trying to figure it out. I know the two smaller connections on the top are the coolant lines and I've tested vacuum on those and its good. The bottom funnel where the hose gets clamped to is the oil return line to the crankcase and the connection that bolts to the engine is the opening for the vapors to go to. That leaves to connections of which one I assume is the vacuum line to the manifold which I'm guessing is the top one, tube 5 in both diagrams. What about the bottom one which is tube 4 in both diagrams? I'm guessing that its the fresh air in? Any ideas where its connected to? Maybe the air filter box?
I've attached a diagram that I found.
Any ideas?
Thanks for all the great info!
First diagram I found. Is this the one for my 2002 C4 Cab with 3.6L engine?
Or is this the correct diagram for my 2002 C4 Cab?
Yes, #5 connects to vacuum. #4 connects to the bank 2 engine case half, basically evacuating oil vapor from there. The bottom opening where #2 o-ring goes onto sits directly on top of the bank 1 engine case so it evacuates oil vapor there.
From those two diagrams it appears one has the coolant lines running through the AOS the other doesn't obviously.
As a fail safe if there are multiple versions of a particular part I ask the OPC parts department to verify which part number is correct against my VIN.
Usually works quite well, you might pay a little bit more than online but at least you know its going to be the right part/version for your particular car.
For 996 (3.4 and 3.6) you want the AOS with the coolant lines. The AOS w/o the coolant line is for Boxsters where the coolant lines are probably not needed due to the location of the AOS.
Thanks! I think I get it now. The coolant lines are there to provide heat so as to make sure the vapor stays vapor and doesn't condense into liquid that would just flow back into the oil. The port with 2 and the tube 4 is where the vapors from the crank case get sucked into the separator via the vacuum pulled on tube 5. Tube 5 pulls the vacuum and the big tube with the funnel on the bottom probably has some sort of corkscrew or something in it that when the vapors swril through it, the oil and vapor separate, the oil collects at the bottom and the funel allows it back into the crankcase.
The upper round part with the coolant connections and the vacuum connection is essentially the PCV valve where the fragile diaphram inside somehow regulates the vacuum pressure to suck in the crank case vapors and the fat tube and funnel it sits on top of is the actual oil/vapor separator. A better design would be to separate the PCV valve into a location easy to replace and run a vacuum hose from that to the separator, which should never fail because there are no moving parts in it.
It is what it is. We'll see tomorrow if I need to change mine out. Thanks!!
Thanks! I think I get it now. The coolant lines are there to provide heat so as to make sure the vapor stays vapor and doesn't condense into liquid that would just flow back into the oil. The port with 2 and the tube 4 is where the vapors from the crank case get sucked into the separator via the vacuum pulled on tube 5. Tube 5 pulls the vacuum and the big tube with the funnel on the bottom probably has some sort of corkscrew or something in it that when the vapors swril through it, the oil and vapor separate, the oil collects at the bottom and the funel allows it back into the crankcase.
The upper round part with the coolant connections and the vacuum connection is essentially the PCV valve where the fragile diaphram inside somehow regulates the vacuum pressure to suck in the crank case vapors and the fat tube and funnel it sits on top of is the actual oil/vapor separator. A better design would be to separate the PCV valve into a location easy to replace and run a vacuum hose from that to the separator, which should never fail because there are no moving parts in it.
It is what it is. We'll see tomorrow if I need to change mine out. Thanks!!
Great write up!
Now if you could transfer all that info with arrows etc. onto the AOS parts diagram for those of us who are more visual ill buy you a beer next time i'm in the US... haha!
Thanks! I think I get it now. The coolant lines are there to provide heat so as to make sure the vapor stays vapor and doesn't condense into liquid that would just flow back into the oil. The port with 2 and the tube 4 is where the vapors from the crank case get sucked into the separator via the vacuum pulled on tube 5. Tube 5 pulls the vacuum and the big tube with the funnel on the bottom probably has some sort of corkscrew or something in it that when the vapors swril through it, the oil and vapor separate, the oil collects at the bottom and the funel allows it back into the crankcase.
The upper round part with the coolant connections and the vacuum connection is essentially the PCV valve where the fragile diaphram inside somehow regulates the vacuum pressure to suck in the crank case vapors and the fat tube and funnel it sits on top of is the actual oil/vapor separator. A better design would be to separate the PCV valve into a location easy to replace and run a vacuum hose from that to the separator, which should never fail because there are no moving parts in it.
It is what it is. We'll see tomorrow if I need to change mine out. Thanks!!
You got everything correct except the coolant part. The coolant is to prevent the water content in the crankcase vapor from freezing up the moving parts inside the AOS in cold climate.
I know this is overkill and may be TMI but for those that care some interesting info as I've heard nothing but cursing of the AOS but turns out that it is a high performance sports car doohicky:
First diagram I found. Is this the one for my 2002 C4 Cab with 3.6L engine?
I can show you were the coolant lines are supposed to go in my previous (evidently) owner modified AOS. (mine is an 04 3.6L C2) Coolant line #12 coming out of the side of the AOS in the above diagram is supposed to go to the connector to the right of the alternator, while line #11 coming from the top goes to a t- just under the coolant resz. I'm guessing in my case, line 12 was cut...about where it is broken in the diagram above, and left hanging. As shown in my photo, the other end of #12 was re-routed to the connection were line #11 was supposed to go, those bypassing the AOS. So the question is- should I reattach it when I put in the new AOS - which BTW is finally unbolted! (I generally don't run the car in subfreezing weather here in Kentucky)
05-16-2017, 12:42 AM
