mecheng is correct. I design fluids based labs for a university dealing with laminar and turbulent flows. The point were the pressure increases is usually the point of "obstruction". You can think of this as an orifice. I just did this fix on my 1998 V70 R AWD with MAJOR oil leaking from the rear cam seal. I was actually planning on commenting back on this about the pressure increase principal but by the time I looked you had posted your correction.
While completing the fix, I noticed that the largest "obstruction" was where the factory 3/8" brittle tube joins to the breather box. Here, you have a large flow rate passing through an obstruction. Bernoulli's equation can reveal that an increase in velocity will cause an increase in pressure [ deltaP=rho(V2^2-V1^2)/2]. We can neglect higher order terms to see how the radius change effects the pressure. So all those molecules have to keep moving at the same MASS flow rate (mdot) which corresponds to Q1=Q2 (m^3/s) (Volumentric flow rate=Q=(mdot/rho)). Also by playing with the units, V1(m/s)*A1(m^2)=V2(m/s)*A2(M^2) which you can see retains the overall units of (m^3/s). So, V2=V1A1/A2. Putting this into Bernoulli's equation, DeltaP=(rho/2)*((V1*A1/A2)^2-V1^2). When A2 is smaller than A1, (A1/A2)>1 which increases the velocity difference (V2^2-V1^2) subsequently raising the pressure. You can find the factor of pressure increase from this equation on the right side, (rho/2)*(V1^2)*[(A1/A2)^2-1] where we assume rho and V1 are constant at an infinitesimal point in time.A=pi*(d/2)^2=pi*(d^2/4) so if the first tube dia. is arbitrarily 1, and the second tube dia. is arbitrarily 0.5, A1=(pi*(1)^2)/4 = 0.785 and A2=(pi*(1/2)^2)/4= 0.19625. Obviously, A1/A2=4 (when D1/D2=2). Substituting this into the other equation above (should have numbered them), DeltaP=[(rho*V1^2)/2]*(16-1) or, DeltaP=15*[(rho*V1^2)/2]. So, a decrease in diameter by a factor of 2 results in 15x increase in pressure, if my very rough calculations are correct. This is also ignoring surface roughness (friction) and the little expansion of the heater hose which is a reasonable assumption.
Now, I did also notice that the PTC has an even smaller "orifice" for air to pass through. However, this area of flow is complex due to the vacuum port as well. The intake vents the pressure here and has an affect on flow velocity. There are ALOT of aspects of this type of calculation involving simulation for varying conditions (CC pressure, PCV gas mass flow rate, intake pressure through vacuum port, and intake pressure through turbo entry tube). All of these aspects would still effect the pressure calculation. So this is not necessarily "accurate" but it does give us an idea of how blockage or obstruction can affect the pressure in the crankcase. This is the same concept of solving that mecheng used but I used Bernoulli's equation to find DeltaP. I'm pretty sure the method mecheng used is for flow rate through a tube with a known pressure drop (likely from surface roughness). That equation is to find the flow rate through a straight tube of constant diameter where the deltaP is a pressure drop usually associated with losses. I've mainly seen this in heat exchanger design for laminer flow through long constant tubes (evaluated for pumping pressure and such). The calculation I just went through looks at the pressure drop between tubes of different diameters which I found more applicable due to the change in the cross sectional area from blockage and tube diameters.
After that lengthy discussion, the results of my fix were excellent. I started with substantial pressure in the crankcase and a lot of oil leaks. I ended with large negative pressure and NO oil leaks. I do believe some of it would have to do with blockage reduction through the heater hose, but the factory design still requires the reduction of flow area into the hard brittle tube from the breather box so it does help the pressure.
In my opinion, this fix WILL reduce the pressure on cold start up AND reduce the probability of blockage occurring. So its a win-win for me. Plus, that hard brittle tube can break if you ever want to get down to service your PCV or remove your intake to turbo tube to service the turbo. So, its a win-win-win. oh yeah, its also cheaper than the factory tube...
DIY: 1998 Volvo S70 GLT PCV Mod: no more smoking dipstick!
This topic is in the MVS Volvo Repair Database »
The Ultimate PCV Fix DIY
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Ben850
- Posts: 1613
- Joined: 8 September 2011
- Year and Model: 1996 850 R Wagon
- Location: Michigan
- Been thanked: 7 times
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Last edited by Ben850 on 08 Dec 2014, 22:59, edited 1 time in total.
1993 850 GLT , You wouldn't know it.
1996 850 Turbo Wagon White.
1995 T-5R Black. New work in progress.
1998 V70 XC Cross Country White.
1994 850 N/A Wagon Black.
1997 850 Sedan Black.
1996 850R Wagon White.
1997 850 Sedan Red ( not white or black!)
1996 850 Turbo Wagon White.
1995 T-5R Black. New work in progress.
1998 V70 XC Cross Country White.
1994 850 N/A Wagon Black.
1997 850 Sedan Black.
1996 850R Wagon White.
1997 850 Sedan Red ( not white or black!)
-
Ben850
- Posts: 1613
- Joined: 8 September 2011
- Year and Model: 1996 850 R Wagon
- Location: Michigan
- Been thanked: 7 times
.
Last edited by Ben850 on 08 Dec 2014, 22:24, edited 1 time in total.
1993 850 GLT , You wouldn't know it.
1996 850 Turbo Wagon White.
1995 T-5R Black. New work in progress.
1998 V70 XC Cross Country White.
1994 850 N/A Wagon Black.
1997 850 Sedan Black.
1996 850R Wagon White.
1997 850 Sedan Red ( not white or black!)
1996 850 Turbo Wagon White.
1995 T-5R Black. New work in progress.
1998 V70 XC Cross Country White.
1994 850 N/A Wagon Black.
1997 850 Sedan Black.
1996 850R Wagon White.
1997 850 Sedan Red ( not white or black!)
-
Ben850
- Posts: 1613
- Joined: 8 September 2011
- Year and Model: 1996 850 R Wagon
- Location: Michigan
- Been thanked: 7 times
.
Last edited by Ben850 on 08 Dec 2014, 22:22, edited 3 times in total.
1993 850 GLT , You wouldn't know it.
1996 850 Turbo Wagon White.
1995 T-5R Black. New work in progress.
1998 V70 XC Cross Country White.
1994 850 N/A Wagon Black.
1997 850 Sedan Black.
1996 850R Wagon White.
1997 850 Sedan Red ( not white or black!)
1996 850 Turbo Wagon White.
1995 T-5R Black. New work in progress.
1998 V70 XC Cross Country White.
1994 850 N/A Wagon Black.
1997 850 Sedan Black.
1996 850R Wagon White.
1997 850 Sedan Red ( not white or black!)
-
Ben850
- Posts: 1613
- Joined: 8 September 2011
- Year and Model: 1996 850 R Wagon
- Location: Michigan
- Been thanked: 7 times
.
Last edited by Ben850 on 08 Dec 2014, 22:22, edited 2 times in total.
1993 850 GLT , You wouldn't know it.
1996 850 Turbo Wagon White.
1995 T-5R Black. New work in progress.
1998 V70 XC Cross Country White.
1994 850 N/A Wagon Black.
1997 850 Sedan Black.
1996 850R Wagon White.
1997 850 Sedan Red ( not white or black!)
1996 850 Turbo Wagon White.
1995 T-5R Black. New work in progress.
1998 V70 XC Cross Country White.
1994 850 N/A Wagon Black.
1997 850 Sedan Black.
1996 850R Wagon White.
1997 850 Sedan Red ( not white or black!)
Wow, I did not intend for all that dialogue to occur after my response. As was stated, both by myself and the original author, this "fix" is for increased blow by usually occurring on start up of the engine. During start up, the combustion chamber is cold and the piston ring end gap is larger causing "increased" blow by. The author also never states that the system is a "clog" fixer. If there are clogs from crud build up, in oil ports running through the engine, those would have to be eradicated by other means beyond the scope of this DIY. This particular article is dealing with a "control volume" around the PCV system (tubes to/from breather to CC and PTC). It does not concern what other problems may occur within every small oil passage.
That being said, the 3/8" dia. brittle plastic tube may have been adequate 15 years ago. Today plastic tubing is made of stronger materials (not my area of expertise). The factory brittle tube, as stated by the author, hardens and cracks over time. It is extremely fragile after the 5-10 yr period. Also, automotive manufactures usually offer a warranty (5 years 100k or something similar). Most companies today (particularly GE appliances) do not design products to last much longer beyond the warranty. The warranty is in place BECAUSE of the material property degradation (which we were taught in material properties). This is why products generally "wear" much quicker after the warranty period (why poorly designed washing machines break 6-12 months after warranty expiration). So, the shortest life ofcritical components determines the effective life of the product. I would expect Volvo of the 90's to have a better quality program than this. None the less, that plastic tube will age, it will get brittle, and it will crack. It is a matter of time, BUT it will happen.
This DIY was originally posted to fix a "smoking dipstick" which I interpret as small amounts of positive crankcase pressure at idle. It is possible that during regular driving (not idle) the engine would have a negative CC pressure under this condition. But, it is unnerving to know that you could have a "time bomb of oil" under your hood. Some have had cam seals blow draining their oil in 5 min and ruining their engine (allegedly).
As I stated, I never intended to "fix" my PCV system initially. I went to clean my PTC nipple and while removing my turbo air intake hose, I heard a snap which was that hard brittle tube cracking. I pulled the end out and felt super bad thinking I just cost myself a lot of time and money. Then I started to think that this was a TERRIBLE design.. I mean a hard plastic tube, right next to the engine, making a 90 degree turn? Heat alone would speed up the degradation process of this tube. Around the 90 degree turn, the flow would become MORE turbulent causing more "fouling" to occur in this area (basic heat exchanger design). This is also confirmed by cracking open an old one of these and looking inside. Further more, there are additional near 90 degree bends at the PTC and breather box. These bends also collected ALOT of deposits obstructing the flow, again physically observed and confirmed by fluid principals.
It is reasonable to assume that instead of making sharp bends, a more gradual curvature would decrease turbulence and deposits. One must also consider the mileage of the vehicle. If the car has 195k (as mine does) and I am assuming that my heater hose will withstand the elements for 5 years (a very reasonable assumption) then I can expect to reach 300k without needing to replace it (I drive 20k a year). Conveniently, if my car does last this long, that's right around the time I would want to re-service my PCV, giving me the opportunity to re-perform the fix. The heater hose is 6 bucks, the factory tube is 45 bucks... You do the math. In addition, most (even us Volvo owners) know that our cars wont last forever and at some point will bite the dust. I honestly do not expect to even get another 100k out of my engine.
So the fix is economical, beneficial and effective for regular PCV service intervals. Why not give it a shot? Sure I read all the negative comments about "oil and heater hose" but really, that old brittle tube literally fits inside the diameter of the heater hose.. If the tube begins to degrade from the oil, what does it matter? The tube will not fully degrade in 5 years, and it will be from the inside out.. which is even better to increase the inner diameter (hopefully you wouldn't suck chunks of tube into turbo). Also, the expansion of the heater hose must be negligible.. I would have expected the hard brittle tube to "explode" if expansion forces were large enough to expand the heater hose significantly...
Furthermore, we don't even care about the internal pressure of the tube.. We care about the internal pressure of the crankcase. The bottleneck of pressure release occurs where this tube connects to the breather box. so the breather box would be "inducing?" a pressure on the crankcase because of the obstruction of flow. I would assume, if the PTC was clear, that the intake (vacuum line and turbo air intake hose) would removing gas faster than it is replenished causing a negative pressure within the tube. The problem is that the breather box cannot allow enough gas into the inlet of the tube to properly vent pressure. This also makes sense because of the sharp curvature of the tube from the breather box. I found SIGNIFICANT obstruction here because of the curve (turbulent flow) which eventually does obstruct the flow more than the 3/8" tube will. Redneck is correct, the ports from and to the crankcase will clog, but the 3/8" dia. tube has a higher probability of clogging due to the reduced diameter. There is just less space for crud to fill (basically neglecting all the crap going to the lower crankcase tube via gravity). None the less, this is still not what the DIY is about! It is not concerned with engine port clogging, but rather the physical components of the PCV vent system (everything after the crankcase).
This is not a DIY to stop the tube from clogging, it is simply designed to improve the airflow of aged high mileage vehicles. Sure the factory tube may be sufficient, but for some, the increased blow by on start up would grow with obstruction of the hard brittle tube around the bends. Increasing diameter increases the bottle neck diameter to that of the breather box outlet diameter (since this fits into the 5/8" heater hose) and it will also increase the time it takes for the tube to become critically obstructed.
Most people who only know "equations" do not think about economical or life expectancy of a fix. In this case, I firmly believe that this is both more economical and a better design to release the pressure over regular PCV service intervals. If the tube does degrade and cracks, it vents to the atmosphere just like through the dip stick (extremely low probability) granted you may have performance related issues. Although the design is not "right", it works, lasts the appropriate amount of time and subsequently is successful.
Car manufacturers look at PCV systems as a thorn.. Its just another regulation vehicles have to pass. I doubt any significant engineering goes into this system (indicated by the "complex".. cough.. cough.. design). This is an extremely simple system. Oftentimes, the best solution is both effective and simple, which equates to cheap.
I never looked up "how to unclog oil passage in engine" or "excessive crankcase pressure" I was in search of advice on how to best fix the PCV system and what other components to replace. Luckily, a member pointed me in this direction and I started connecting dots between my engine symptoms and the options to alleviate them.
In summary, don't forget the subject of this DIY "to fix a smoking dipstick" with no indication as to CC pressure (although it is caused by minor CC pressure). This is in no way intended to "fix" clogs within an engine.. that is beyond the scope of this DIY. Ultimately, to each his (or her) own. You can decide how to fix your system. The reasonable success of this DIY would suggest it is a significant fix. There is only so much engineering that can go into a simple system; in which case, it is a good to know what just works for the intended design.
That being said, the 3/8" dia. brittle plastic tube may have been adequate 15 years ago. Today plastic tubing is made of stronger materials (not my area of expertise). The factory brittle tube, as stated by the author, hardens and cracks over time. It is extremely fragile after the 5-10 yr period. Also, automotive manufactures usually offer a warranty (5 years 100k or something similar). Most companies today (particularly GE appliances) do not design products to last much longer beyond the warranty. The warranty is in place BECAUSE of the material property degradation (which we were taught in material properties). This is why products generally "wear" much quicker after the warranty period (why poorly designed washing machines break 6-12 months after warranty expiration). So, the shortest life ofcritical components determines the effective life of the product. I would expect Volvo of the 90's to have a better quality program than this. None the less, that plastic tube will age, it will get brittle, and it will crack. It is a matter of time, BUT it will happen.
This DIY was originally posted to fix a "smoking dipstick" which I interpret as small amounts of positive crankcase pressure at idle. It is possible that during regular driving (not idle) the engine would have a negative CC pressure under this condition. But, it is unnerving to know that you could have a "time bomb of oil" under your hood. Some have had cam seals blow draining their oil in 5 min and ruining their engine (allegedly).
As I stated, I never intended to "fix" my PCV system initially. I went to clean my PTC nipple and while removing my turbo air intake hose, I heard a snap which was that hard brittle tube cracking. I pulled the end out and felt super bad thinking I just cost myself a lot of time and money. Then I started to think that this was a TERRIBLE design.. I mean a hard plastic tube, right next to the engine, making a 90 degree turn? Heat alone would speed up the degradation process of this tube. Around the 90 degree turn, the flow would become MORE turbulent causing more "fouling" to occur in this area (basic heat exchanger design). This is also confirmed by cracking open an old one of these and looking inside. Further more, there are additional near 90 degree bends at the PTC and breather box. These bends also collected ALOT of deposits obstructing the flow, again physically observed and confirmed by fluid principals.
It is reasonable to assume that instead of making sharp bends, a more gradual curvature would decrease turbulence and deposits. One must also consider the mileage of the vehicle. If the car has 195k (as mine does) and I am assuming that my heater hose will withstand the elements for 5 years (a very reasonable assumption) then I can expect to reach 300k without needing to replace it (I drive 20k a year). Conveniently, if my car does last this long, that's right around the time I would want to re-service my PCV, giving me the opportunity to re-perform the fix. The heater hose is 6 bucks, the factory tube is 45 bucks... You do the math. In addition, most (even us Volvo owners) know that our cars wont last forever and at some point will bite the dust. I honestly do not expect to even get another 100k out of my engine.
So the fix is economical, beneficial and effective for regular PCV service intervals. Why not give it a shot? Sure I read all the negative comments about "oil and heater hose" but really, that old brittle tube literally fits inside the diameter of the heater hose.. If the tube begins to degrade from the oil, what does it matter? The tube will not fully degrade in 5 years, and it will be from the inside out.. which is even better to increase the inner diameter (hopefully you wouldn't suck chunks of tube into turbo). Also, the expansion of the heater hose must be negligible.. I would have expected the hard brittle tube to "explode" if expansion forces were large enough to expand the heater hose significantly...
Furthermore, we don't even care about the internal pressure of the tube.. We care about the internal pressure of the crankcase. The bottleneck of pressure release occurs where this tube connects to the breather box. so the breather box would be "inducing?" a pressure on the crankcase because of the obstruction of flow. I would assume, if the PTC was clear, that the intake (vacuum line and turbo air intake hose) would removing gas faster than it is replenished causing a negative pressure within the tube. The problem is that the breather box cannot allow enough gas into the inlet of the tube to properly vent pressure. This also makes sense because of the sharp curvature of the tube from the breather box. I found SIGNIFICANT obstruction here because of the curve (turbulent flow) which eventually does obstruct the flow more than the 3/8" tube will. Redneck is correct, the ports from and to the crankcase will clog, but the 3/8" dia. tube has a higher probability of clogging due to the reduced diameter. There is just less space for crud to fill (basically neglecting all the crap going to the lower crankcase tube via gravity). None the less, this is still not what the DIY is about! It is not concerned with engine port clogging, but rather the physical components of the PCV vent system (everything after the crankcase).
This is not a DIY to stop the tube from clogging, it is simply designed to improve the airflow of aged high mileage vehicles. Sure the factory tube may be sufficient, but for some, the increased blow by on start up would grow with obstruction of the hard brittle tube around the bends. Increasing diameter increases the bottle neck diameter to that of the breather box outlet diameter (since this fits into the 5/8" heater hose) and it will also increase the time it takes for the tube to become critically obstructed.
Most people who only know "equations" do not think about economical or life expectancy of a fix. In this case, I firmly believe that this is both more economical and a better design to release the pressure over regular PCV service intervals. If the tube does degrade and cracks, it vents to the atmosphere just like through the dip stick (extremely low probability) granted you may have performance related issues. Although the design is not "right", it works, lasts the appropriate amount of time and subsequently is successful.
Car manufacturers look at PCV systems as a thorn.. Its just another regulation vehicles have to pass. I doubt any significant engineering goes into this system (indicated by the "complex".. cough.. cough.. design). This is an extremely simple system. Oftentimes, the best solution is both effective and simple, which equates to cheap.
I never looked up "how to unclog oil passage in engine" or "excessive crankcase pressure" I was in search of advice on how to best fix the PCV system and what other components to replace. Luckily, a member pointed me in this direction and I started connecting dots between my engine symptoms and the options to alleviate them.
In summary, don't forget the subject of this DIY "to fix a smoking dipstick" with no indication as to CC pressure (although it is caused by minor CC pressure). This is in no way intended to "fix" clogs within an engine.. that is beyond the scope of this DIY. Ultimately, to each his (or her) own. You can decide how to fix your system. The reasonable success of this DIY would suggest it is a significant fix. There is only so much engineering that can go into a simple system; in which case, it is a good to know what just works for the intended design.
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