howardc64
11-15-2015, 11:25 AM
As these cars get up in miles, more and more people need to do their PCV system. I've recently gone into quite a bit of detail on the PCV system and like to share some info and dispel any mythes. This is my working understanding. Please chime in if anyone has different understanding.
In addition, I like to propose a more definitive PCV test. I've collected 2 samples using this test and like to get more. So perhaps people can try this simple test and report back.
So onto the PCV design and function.
Blowby Pressure
Without going into much detail. There will be slight gasses leaking past the piston rings during its operation. This naturally increases the pressure in the crankcase and need to be exit somewhere so PCV system is basically the air channel design to vent this pressure. If PCV system becomes restricted (even partially), pressure will increase. Its same principle as if you put your thumb over a garden hose to create high pressure flow.
Intake Manifold Vacuum on Turbo Cars
IM is a great source of vacuum. Pistons draws in air on the intake cycle with throttle body plate being the air flow limiter. This produces a lot of vacuum and is used for PCV, EVAP, turbo CBV (compression bypass valve), and brake booster. However, the IM vacuum goes away and turns pressurized on turbo charged cars under boost. This means all things that use this vacuum source need an alternative solution under boost conditions.
The easiest way to see this vacuum/pressure response in IM is to tap the IM at the CBV vacuum port. T this port and run a hose into into the cabin into a vacuum/pressure gauge. The vacuum/pressure dial basically responds to the accelerator. Applying accel moves the dial from vacuum to neutral to pressure.
PCV's Idle Circuit
When IM has good vacuum, PCV system uses this source to vent the blowby.
PCV's Boost Circuit
When IM is pressurized, PCV system needs alternative air channel to get rid of the blowby pressure. PCV's boost circuit basically creates a vent to front (air intake side) of the turbo to vent it. I've come to realize this is NOT a high vacuum source like IM because while turbo sucks in air, the air filter, air box and its air hose from the grill isn't much of a restriction. Thus the vacuum source to the boost circuit is relatively low. It is more of a venting port than say a vacuum source.
What this means is you don't get negative PCV pressure during the entire drive cycle. A healthy PCV system should yield a little bit of positive pressure and this is okay! Many people believe it should always be vacuum and I think this is myth.
There has also been observations Volvo's OEM sized boost circuit channel may not be sufficient as the engine wear gets up in age and require greater flow rate to vent the higher bypass.
Diagram
Now onto a diagram to explain this complicated things
http://img.photobucket.com/albums/v17/rufe_v6/pcvinfo3.jpg
IM vacuum source is a 2mm air channel between the 2 #10 washers sandwiched by the #11 banjo bolt (towards the front of the car in this diagram). Here are 2 close up pics. First one has a line running through this channel to ensure its clear. 2nd pic shows the hose pulled off and the 2mm channel is inside of that barbed connection.
Over the years, Volvo tweaked the PCV system. On the earlier P2s, the original Banjo bolt has an internal open air channel while later models includes a check ball. I think the reason for the check ball is to prevent the pressure from entering the boost circuit when IM is pressurized. But I suppose the boost circuit is sized large enough to vent both the crank case pressure and IM pressure under boost on older cars.
http://www.2carpros.com/forum/automotive_pictures/337695_IMG00141_1.jpg
https://live.staticflickr.com/65535/50220182987_2cf4f3fd4c.jpg (https://flic.kr/p/2jvMyKV)DSCF4061 (https://flic.kr/p/2jvMyKV)
Boost circuit is basically an aluminum pipe that runs inside of #8 and exit at clamp #13. Its clamped to the PTC nipple (more on this later) On a recent 2000 V70XC I worked on, this aluminum pipe is a relatively narrow 3/8" ID.
Blowby gasses flows out of the block at the port clamped by #3 clamp and on the head at clamp #7. They both go into the oil trap (#1). These gasses has oily vapor in them and need to be filtered out and returned back to the engine oil while the pressurized air and various gasoline consumption byproduct gets sent back into the engine to be consumed again. The filtered out oil drains back into the oil pan at #4. Here is a picture of the oil trap internals, its design to route blowby gasses around some turns and have the oil vapor collect on the walls and drip down into the drain port.
http://volvoforums.com/forum/attachments/volvo-850-16/11451d1423527715-pcv-system-parts-pcv-cutaway.jpg
There is a complex drain channel inside the block and oil pan (At least 2 or 3 90 degree turns) and can clog/narrow the drain channel there. Dropping the oil pan is necessary to clear out this drain channel. I blew some air into the drain port and heard oil bubbling inside to ensure it was clear. Another member did the same and heard oil bubbling but decided to pull the pan and found partial restrictions. So you'll have to decide what you are comfortable with and how much effort to put in. Here are some pictures of this drain channel
Lower red circle is the where the oil trap returns the oil.
http://www.tracystruesoaps.com/tutorials/850hg/pcv_oil_trap_conn_to_engine.jpg
Long rectangular drain channel inside the block (this one is completely blocked)
http://www.brakeandfrontend.com/wp-content/uploads/Articles/03_01_2009/93623Photo11jpg_00000047480.jpg
Another rectangular channel inside the pan. It eventually gets to the bottom and I believe makes another turn towards an upward facing exit.
http://www.atlanticmotorcar.com/wp-content/uploads/DSC04815.jpg
There are other lines in this PCV diagram and they are for coolant flow. Volvo thought it was a good idea to warm the PCV air to reduce condensation and therefore clogging. I'd imagine it quite a bit of over design complexity. This whole area is tucked under the intake manifold, it gets hot quick down there :)
Test
The simple glove test (wrap a latex glove over the oil filler hole) basically check the idle circuits vacuum. Revving the engine in park doesn't use the boost circult. You have to put the car in D, step on the brakes and gas it up to 2k+ RPM to enable the boost circuit. Needless to say you can't do this very long as it puts stress on the torque converter. Certainly not long enough to get a feel of how the boost circuit works in operation.
A much better test is to take out the oil dip stick, route a long rubber/silicon tubing (5mm ID silicon tube works well) from oil dip stick port (jam the tubing in there to create a good seal) into the cabin with a latex glove rubber band to the end. You can't lock down the hood as hood seals would crimp the hose and also have to route the hose to avoid crimping. Now go for a drive, you can see PCV operation under idle, boost, and cruise.
In the 2 cars I've seen this setup on with a healthy PCV system, glove definitely inflates under boost/cruise but its clear its not very high pressure. At times, it seems to have a mind of its own (maybe changing in relation to CVVT?) and doesn't exactly match the accelerator. Anyway, I consulted with a Volvo tech (cattlecar here), he said inflation is okay, just can't be high pressure.
One way to make sure there is no high pressure is to swap the glove for a typical vacuum/pressure gauge. You definitely don't want to see the needle move much at all. Nothing even close to 1/2 PSI.
Anyway, this makes sense, boost circuit is mostly a vent, not a vacuum port. A little positive pressure is to be expected. Would be great if others can run this test and we can collectively get more statistics.
Increasing the boost circuit channel flow
I've read/done resizing the boost circuit channel (using a 5/8" ID heater hose rather than Volvo's stock 3/8" ID pipe) on a 2000XC and definitely vents better (glove inflates less in above test). Another person drilled the PTC nipple's round restrictor hole bigger and also got less inflation.
Anyways, hope this helps understanding this circuit and we get more stats on the above PCV test methodology. You might also ask what happens to EVAP, brake booster and turbo CBV when IM is pressurized? More complexity and I'll skip that here :)
In addition, I like to propose a more definitive PCV test. I've collected 2 samples using this test and like to get more. So perhaps people can try this simple test and report back.
So onto the PCV design and function.
Blowby Pressure
Without going into much detail. There will be slight gasses leaking past the piston rings during its operation. This naturally increases the pressure in the crankcase and need to be exit somewhere so PCV system is basically the air channel design to vent this pressure. If PCV system becomes restricted (even partially), pressure will increase. Its same principle as if you put your thumb over a garden hose to create high pressure flow.
Intake Manifold Vacuum on Turbo Cars
IM is a great source of vacuum. Pistons draws in air on the intake cycle with throttle body plate being the air flow limiter. This produces a lot of vacuum and is used for PCV, EVAP, turbo CBV (compression bypass valve), and brake booster. However, the IM vacuum goes away and turns pressurized on turbo charged cars under boost. This means all things that use this vacuum source need an alternative solution under boost conditions.
The easiest way to see this vacuum/pressure response in IM is to tap the IM at the CBV vacuum port. T this port and run a hose into into the cabin into a vacuum/pressure gauge. The vacuum/pressure dial basically responds to the accelerator. Applying accel moves the dial from vacuum to neutral to pressure.
PCV's Idle Circuit
When IM has good vacuum, PCV system uses this source to vent the blowby.
PCV's Boost Circuit
When IM is pressurized, PCV system needs alternative air channel to get rid of the blowby pressure. PCV's boost circuit basically creates a vent to front (air intake side) of the turbo to vent it. I've come to realize this is NOT a high vacuum source like IM because while turbo sucks in air, the air filter, air box and its air hose from the grill isn't much of a restriction. Thus the vacuum source to the boost circuit is relatively low. It is more of a venting port than say a vacuum source.
What this means is you don't get negative PCV pressure during the entire drive cycle. A healthy PCV system should yield a little bit of positive pressure and this is okay! Many people believe it should always be vacuum and I think this is myth.
There has also been observations Volvo's OEM sized boost circuit channel may not be sufficient as the engine wear gets up in age and require greater flow rate to vent the higher bypass.
Diagram
Now onto a diagram to explain this complicated things
http://img.photobucket.com/albums/v17/rufe_v6/pcvinfo3.jpg
IM vacuum source is a 2mm air channel between the 2 #10 washers sandwiched by the #11 banjo bolt (towards the front of the car in this diagram). Here are 2 close up pics. First one has a line running through this channel to ensure its clear. 2nd pic shows the hose pulled off and the 2mm channel is inside of that barbed connection.
Over the years, Volvo tweaked the PCV system. On the earlier P2s, the original Banjo bolt has an internal open air channel while later models includes a check ball. I think the reason for the check ball is to prevent the pressure from entering the boost circuit when IM is pressurized. But I suppose the boost circuit is sized large enough to vent both the crank case pressure and IM pressure under boost on older cars.
http://www.2carpros.com/forum/automotive_pictures/337695_IMG00141_1.jpg
https://live.staticflickr.com/65535/50220182987_2cf4f3fd4c.jpg (https://flic.kr/p/2jvMyKV)DSCF4061 (https://flic.kr/p/2jvMyKV)
Boost circuit is basically an aluminum pipe that runs inside of #8 and exit at clamp #13. Its clamped to the PTC nipple (more on this later) On a recent 2000 V70XC I worked on, this aluminum pipe is a relatively narrow 3/8" ID.
Blowby gasses flows out of the block at the port clamped by #3 clamp and on the head at clamp #7. They both go into the oil trap (#1). These gasses has oily vapor in them and need to be filtered out and returned back to the engine oil while the pressurized air and various gasoline consumption byproduct gets sent back into the engine to be consumed again. The filtered out oil drains back into the oil pan at #4. Here is a picture of the oil trap internals, its design to route blowby gasses around some turns and have the oil vapor collect on the walls and drip down into the drain port.
http://volvoforums.com/forum/attachments/volvo-850-16/11451d1423527715-pcv-system-parts-pcv-cutaway.jpg
There is a complex drain channel inside the block and oil pan (At least 2 or 3 90 degree turns) and can clog/narrow the drain channel there. Dropping the oil pan is necessary to clear out this drain channel. I blew some air into the drain port and heard oil bubbling inside to ensure it was clear. Another member did the same and heard oil bubbling but decided to pull the pan and found partial restrictions. So you'll have to decide what you are comfortable with and how much effort to put in. Here are some pictures of this drain channel
Lower red circle is the where the oil trap returns the oil.
http://www.tracystruesoaps.com/tutorials/850hg/pcv_oil_trap_conn_to_engine.jpg
Long rectangular drain channel inside the block (this one is completely blocked)
http://www.brakeandfrontend.com/wp-content/uploads/Articles/03_01_2009/93623Photo11jpg_00000047480.jpg
Another rectangular channel inside the pan. It eventually gets to the bottom and I believe makes another turn towards an upward facing exit.
http://www.atlanticmotorcar.com/wp-content/uploads/DSC04815.jpg
There are other lines in this PCV diagram and they are for coolant flow. Volvo thought it was a good idea to warm the PCV air to reduce condensation and therefore clogging. I'd imagine it quite a bit of over design complexity. This whole area is tucked under the intake manifold, it gets hot quick down there :)
Test
The simple glove test (wrap a latex glove over the oil filler hole) basically check the idle circuits vacuum. Revving the engine in park doesn't use the boost circult. You have to put the car in D, step on the brakes and gas it up to 2k+ RPM to enable the boost circuit. Needless to say you can't do this very long as it puts stress on the torque converter. Certainly not long enough to get a feel of how the boost circuit works in operation.
A much better test is to take out the oil dip stick, route a long rubber/silicon tubing (5mm ID silicon tube works well) from oil dip stick port (jam the tubing in there to create a good seal) into the cabin with a latex glove rubber band to the end. You can't lock down the hood as hood seals would crimp the hose and also have to route the hose to avoid crimping. Now go for a drive, you can see PCV operation under idle, boost, and cruise.
In the 2 cars I've seen this setup on with a healthy PCV system, glove definitely inflates under boost/cruise but its clear its not very high pressure. At times, it seems to have a mind of its own (maybe changing in relation to CVVT?) and doesn't exactly match the accelerator. Anyway, I consulted with a Volvo tech (cattlecar here), he said inflation is okay, just can't be high pressure.
One way to make sure there is no high pressure is to swap the glove for a typical vacuum/pressure gauge. You definitely don't want to see the needle move much at all. Nothing even close to 1/2 PSI.
Anyway, this makes sense, boost circuit is mostly a vent, not a vacuum port. A little positive pressure is to be expected. Would be great if others can run this test and we can collectively get more statistics.
Increasing the boost circuit channel flow
I've read/done resizing the boost circuit channel (using a 5/8" ID heater hose rather than Volvo's stock 3/8" ID pipe) on a 2000XC and definitely vents better (glove inflates less in above test). Another person drilled the PTC nipple's round restrictor hole bigger and also got less inflation.
Anyways, hope this helps understanding this circuit and we get more stats on the above PCV test methodology. You might also ask what happens to EVAP, brake booster and turbo CBV when IM is pressurized? More complexity and I'll skip that here :)