Is it safe to install an oil catch can?
- Thread starter kilou
- Start date
- Status
BlazerLT, did you check crankcase vacuum both at idle and under load? How much vacuum (inch of water) does your car pulls at idle/load?
OK, I'm back from my not-overly-scientific test.
My engine appears to behave quite differently from kilou's.
When I removed my dipstick on the idling engine, the crankcase gases began to literally blow out of the hole. OK, they don't blow the dipstick out, but there is no vacuum for sure. This is with, and without the catch can, at any RPM.
The dipstick shaft begins at the valve cover and goes through the head right into the oil pan. May be that makes a difference?..
There's quite strong vacuum at PCV valve at the valve cover (measured with a tee). A bit stronger without catch can, but not by much. The engine wants to quit right away if PCV hose gets an open end, which is normal, I suppose. The flow increases with RPM, the vacuum increases a little too.
I can see the flow through the catch can. If there is residue in the can, the stream of gases disturbs the oil surface, so I can make a judgment about the flow rate.
The fresh air tube from before the butterfly valve to the valve cover does suck air, with and without the catch can, at any RPM. Of course I run the test with no load, so at WOT this could be a different story. The air flow and vacuum rate there appears to be much smaller then at PCV tube.
So, I conclude that my catch can setup does not affect PCV system very much. Although I don't understand why the crankcase is under some pressure? Is it normal? I thought that PCV system creates a slight vacuum throughout the engine, and not just in the head?..
BTW, my engine is squeaky clean from inside, having conservative OCIs of mostly M1, GC, XD-3 during its 100k km service so far.
My engine appears to behave quite differently from kilou's.
When I removed my dipstick on the idling engine, the crankcase gases began to literally blow out of the hole. OK, they don't blow the dipstick out, but there is no vacuum for sure. This is with, and without the catch can, at any RPM.
The dipstick shaft begins at the valve cover and goes through the head right into the oil pan. May be that makes a difference?..
There's quite strong vacuum at PCV valve at the valve cover (measured with a tee). A bit stronger without catch can, but not by much. The engine wants to quit right away if PCV hose gets an open end, which is normal, I suppose. The flow increases with RPM, the vacuum increases a little too.
I can see the flow through the catch can. If there is residue in the can, the stream of gases disturbs the oil surface, so I can make a judgment about the flow rate.
The fresh air tube from before the butterfly valve to the valve cover does suck air, with and without the catch can, at any RPM. Of course I run the test with no load, so at WOT this could be a different story. The air flow and vacuum rate there appears to be much smaller then at PCV tube.
So, I conclude that my catch can setup does not affect PCV system very much. Although I don't understand why the crankcase is under some pressure? Is it normal? I thought that PCV system creates a slight vacuum throughout the engine, and not just in the head?..
BTW, my engine is squeaky clean from inside, having conservative OCIs of mostly M1, GC, XD-3 during its 100k km service so far.
Yugrus, I'm no expert but as far as I know if you have blowby gases blowing out of the dipstick hole it means (as you stated above) you have a pressurized crankcase....which means normally a clogged PCV system! You valve seem fine but have you checked the PCV hoses to see if they are clogged? Does your car have a stock oil trap (to condense oil vapor and return them to the sump, my Volvo has this system)? If you have one check if it's clogged. I've never heard of positive crankcase pressure being a good thing....
Well I did some testing myself this weekend with the new "design" of my catch can and results are....a big surprise!! I'm trying to put this together now and let you know in a few minutes.
Well I did some testing myself this weekend with the new "design" of my catch can and results are....a big surprise!! I'm trying to put this together now and let you know in a few minutes.
---------------- CRANKCASE VACUUM TEST RESULTS -------------
Here are the results from tests . The purpose of this test is to assess if and how the oil catch can affects/restricts the vacuum available in the crankcase and thus how the flow of blowby gases is disturbed. I compared the stock setup with a modified version of my catch can install which I'll illustrate below. You'll find all the details hereafter:
1. Car:
1997 Volvo S40 2.0 (normally aspirated engine, not available in US/Canada!)
2. Mileage:
260,000km
3. Oil catch can:
home-made with Husky filter for air tools available at Home Depot. I removed the stone filter inside but kept the plastic "gear-like" ring and the plastic retaining screw.
4. Vacuum measuring "device":
Home-made vacuum gauge with a plastic tube in U-shape filled with water. One end of the tube is "plugged" to the dipstick hole, the other end is opened to atmospheric pressure.
5. Measure:
I measured CRANKCASE VACUUM through the dipstick hole. I tested this vacuum both AT IDLE and AT 2000rpm with and without the oil catch can.
6. Illustration of stock setup:
Here is an illustration of the junction of PCV hose and vacuum sources near the intake manifold/intake duct. This is the STOCK INSTALL:
7. Illustration of the modified junction with the addition of the oil catch can. Basically the Husky filter has been modified to replace the stock part that makes the junction of all hoses. I had to drill the metal cover of the Husky filter and insert a brass tube that would provide aspiration directly from the intake manifold (blue arrow).
8. Results of crankcase vacuum readings from dipstick hole:
Note: the measure is the negative (vacuum) displacement of water ON ONE SIDE OF THE TUBE ONLY!!!! To get the real vacuum these numbers should be multiplied by 2. Since we are only comparing things here, we don't care.
STOCK INSTALL:
- at idle: 7 mm water
- at 2000rpm: 5 mm water
WITH OIL CATCH CAN:
- at idle: 16 mm water
- at 2000rpm: 11 mm water
9. Conclusions:
Two major conclusions can be drawn from the above results:
A) Crankcase vacuum at idle is HIGHER than at 2000rpm!
My understanding of this is that intake manifold vacuum is also higher when the throttle is closed (at idle) so it's fairly consistent. However this may be different for people who have a valve on their PCV system (I don't) as the valve may regulate this differently.
B) Crankcase vacuum WITH the oil catch can is now TWICE HIGHER than stock!!!!!!!!
This is the weird part! I was first thinking that I'd get a lower crankcase vacuum with the oil catch can installed since air has to go trough more bends than with the stock setup. When I tested my first design (which contained much more bends with additive piping) a few weeks ago I got almost NO vacuum at idle. This was consistent with bends in the system causing a drop of vacuum and reducing the efficiency of the PCV system (less aspiration). Now with the new oil catch can design, the crankcase vacuum is twice the one I get with the stock install!!! I have no real idea of what is causing this but I measured this several times and always get the same results! The only thing I can think of is that the brass pipe I added by drilling the Husky filter top is able to create a stronger vacuum in the bowl than what the stock install can achieve.
Basically my catch can should provide a higher efficiency in every aspects: first it condense oil vapors in blowby gases and it is able to pulls more blowby gases from the crankcase, both at idle and under load. This is VERY good...........but is it not causing too much vacuum in the crankcase? Is it sucking too much blowby gases, especially at idle when you don't want to mess with the air/fuel ratio too much (from the readings I may get 2x more blowby gases at idle too with the oil catch can installed)? I'm thinking of adding a small butterfly tap on the small pipe providing vacuum to the bowl (blue arrow) to fine tune the amount of "vacuum" and make it similar to stock conditions (this would be similar to using a vacuum pipe of smaller diameter).
Anyway I would be glad if someone could explain me in details WHY and HOW I get more vacuum with the oil catch can than without it!!!!
This oil catch can thing is getting me crazy!
Here are the results from tests . The purpose of this test is to assess if and how the oil catch can affects/restricts the vacuum available in the crankcase and thus how the flow of blowby gases is disturbed. I compared the stock setup with a modified version of my catch can install which I'll illustrate below. You'll find all the details hereafter:
1. Car:
1997 Volvo S40 2.0 (normally aspirated engine, not available in US/Canada!)
2. Mileage:
260,000km
3. Oil catch can:
home-made with Husky filter for air tools available at Home Depot. I removed the stone filter inside but kept the plastic "gear-like" ring and the plastic retaining screw.
4. Vacuum measuring "device":
Home-made vacuum gauge with a plastic tube in U-shape filled with water. One end of the tube is "plugged" to the dipstick hole, the other end is opened to atmospheric pressure.
5. Measure:
I measured CRANKCASE VACUUM through the dipstick hole. I tested this vacuum both AT IDLE and AT 2000rpm with and without the oil catch can.
6. Illustration of stock setup:
Here is an illustration of the junction of PCV hose and vacuum sources near the intake manifold/intake duct. This is the STOCK INSTALL:
7. Illustration of the modified junction with the addition of the oil catch can. Basically the Husky filter has been modified to replace the stock part that makes the junction of all hoses. I had to drill the metal cover of the Husky filter and insert a brass tube that would provide aspiration directly from the intake manifold (blue arrow).
8. Results of crankcase vacuum readings from dipstick hole:
Note: the measure is the negative (vacuum) displacement of water ON ONE SIDE OF THE TUBE ONLY!!!! To get the real vacuum these numbers should be multiplied by 2. Since we are only comparing things here, we don't care.
STOCK INSTALL:
- at idle: 7 mm water
- at 2000rpm: 5 mm water
WITH OIL CATCH CAN:
- at idle: 16 mm water
- at 2000rpm: 11 mm water
9. Conclusions:
Two major conclusions can be drawn from the above results:
A) Crankcase vacuum at idle is HIGHER than at 2000rpm!
My understanding of this is that intake manifold vacuum is also higher when the throttle is closed (at idle) so it's fairly consistent. However this may be different for people who have a valve on their PCV system (I don't) as the valve may regulate this differently.
B) Crankcase vacuum WITH the oil catch can is now TWICE HIGHER than stock!!!!!!!!
This is the weird part! I was first thinking that I'd get a lower crankcase vacuum with the oil catch can installed since air has to go trough more bends than with the stock setup. When I tested my first design (which contained much more bends with additive piping) a few weeks ago I got almost NO vacuum at idle. This was consistent with bends in the system causing a drop of vacuum and reducing the efficiency of the PCV system (less aspiration). Now with the new oil catch can design, the crankcase vacuum is twice the one I get with the stock install!!! I have no real idea of what is causing this but I measured this several times and always get the same results! The only thing I can think of is that the brass pipe I added by drilling the Husky filter top is able to create a stronger vacuum in the bowl than what the stock install can achieve.
Basically my catch can should provide a higher efficiency in every aspects: first it condense oil vapors in blowby gases and it is able to pulls more blowby gases from the crankcase, both at idle and under load. This is VERY good...........but is it not causing too much vacuum in the crankcase? Is it sucking too much blowby gases, especially at idle when you don't want to mess with the air/fuel ratio too much (from the readings I may get 2x more blowby gases at idle too with the oil catch can installed)? I'm thinking of adding a small butterfly tap on the small pipe providing vacuum to the bowl (blue arrow) to fine tune the amount of "vacuum" and make it similar to stock conditions (this would be similar to using a vacuum pipe of smaller diameter).
Anyway I would be glad if someone could explain me in details WHY and HOW I get more vacuum with the oil catch can than without it!!!!
This oil catch can thing is getting me crazy!
This explains quite well the two different PCV systems (with or without PCV valve):
http://www.autoshop101.com/forms/h63.pdf
My system is of the "fixed orifice" type and thus does not use a PCV valve. This exactly explains why I have a higher crankcase vacuum at idle than at 2000rpm (because I have no valve to correct this. So my crankcase vacuum varies proportionally to the intake manifold vacuum). That is an "old styled" PCV system not very optimal but it works.
Now that still doesn't explain why I get more crankcase vacuum with the oil catch can than without it! I'll have to carefully check if I have a small vacuum leak with the stock setup maybe....
http://www.autoshop101.com/forms/h63.pdf
My system is of the "fixed orifice" type and thus does not use a PCV valve. This exactly explains why I have a higher crankcase vacuum at idle than at 2000rpm (because I have no valve to correct this. So my crankcase vacuum varies proportionally to the intake manifold vacuum). That is an "old styled" PCV system not very optimal but it works.
Now that still doesn't explain why I get more crankcase vacuum with the oil catch can than without it! I'll have to carefully check if I have a small vacuum leak with the stock setup maybe....
I think that is the case.
I always had two source of vacuum. Look at the stock setup: vacuum is provided both before the throttle body (green arrow) and after the throttle body (blue arrow). Fixed orifice PCV systems such as mine always use too source of vacuum. There must be another explanation.
it's safe, just remember that if you live in california to remove it prior to smog inspection - california likes the oil to be burned and put into the atmosphere.
I finally found why I had a higher crankcase vacuum with the oil catch can than without it! I had no vacuum leak on the stock install so the answer was somewhere else. Basically it is a matter of flow restriction:
I made a slight error on the description of my system. On my fixed orifice PCV system, the vacuum is provided by the small pipe that is connected to the intake manifold. At idle this small pipe sucks a mix of blowby gases (from PCV hose) and fresh air (from the tube connected to the intake duct). So the crankcase vacuum is also regulated by how much fresh air is allowed to be sucked by the small pipe: the more fresh air, the lower crankcase vacuum. With the oil catch can, the fresh air input coming in the bowl via the second opening of the filter (where the green arrow is) was restricted by the small plastic nut retaining the gear-like ring. This made a restriction on the fresh air flow in the bowl and thus more vacuum was directed toward the crankcase. I then removed the plastic nut (which was restricting the diameter of the openeing by about 1mm) and immediately had a lower crankcase vacuum, but it still remained higher than stock. So now I have to figure out how to allow more fresh air in the bowl to lower crankcase vacuum....or restrict the flow on the PCV hose to allow more fresh air etc but I don't like the idea of restricting the flow of blowby gases even if the final purpose is to achieve the same crankcase vacuum reading than stock.
Huh this is really getting crazy! For now I won't use the oil catch can and make a pause because I don't want to mess the air/blowby ratio too much. This fix orifice PCV system is not the best to add a catch can on I guess. You guys with PCV valves might be more lucky than I am
I made a slight error on the description of my system. On my fixed orifice PCV system, the vacuum is provided by the small pipe that is connected to the intake manifold. At idle this small pipe sucks a mix of blowby gases (from PCV hose) and fresh air (from the tube connected to the intake duct). So the crankcase vacuum is also regulated by how much fresh air is allowed to be sucked by the small pipe: the more fresh air, the lower crankcase vacuum. With the oil catch can, the fresh air input coming in the bowl via the second opening of the filter (where the green arrow is) was restricted by the small plastic nut retaining the gear-like ring. This made a restriction on the fresh air flow in the bowl and thus more vacuum was directed toward the crankcase. I then removed the plastic nut (which was restricting the diameter of the openeing by about 1mm) and immediately had a lower crankcase vacuum, but it still remained higher than stock. So now I have to figure out how to allow more fresh air in the bowl to lower crankcase vacuum....or restrict the flow on the PCV hose to allow more fresh air etc but I don't like the idea of restricting the flow of blowby gases even if the final purpose is to achieve the same crankcase vacuum reading than stock.
Huh this is really getting crazy! For now I won't use the oil catch can and make a pause because I don't want to mess the air/blowby ratio too much. This fix orifice PCV system is not the best to add a catch can on I guess. You guys with PCV valves might be more lucky than I am
Why don't you use a tee on the catch can outlet to plug in the smaller diameter tube that goes after the throttle valve? That way you wouldn't have to drill the catch can, right? Am I missing something?
Right but then I will probably suck more fresh air than blowby gases and the crankcase vacuum would be way too low. Drilling the top of the filter is not really the problem, actually it fits very well with the different original pipes and I do not need to add additional pipings. My concern is that I may not use the plastic gear-like ring since the retaining nut restricts the flow too much. I will probably have to find another way to hold the plastic ring (that is supposed to improve condensation in the bowl) and redrill the top of the filter to place the small pipe somewhere else, where it can suck the correct ratio of fresh air and blowby to achieve a similar crankcase vacuum to stock conditions.
Well since my PCV is not fitted with a valve, more vacuum at idle means more blowby gases sucked at idle too, which is not too good. I wouldn't mind having a higher vacuum on high rpm only where most blowby occurs, but not really at idle. Will need to experiment a little bit but this fix orifice design is quite easily affected by an aftermarket catch can. It seems everything is a balance between fresh air and blowby and that adding an oil catch can do this may disrupt this "equilibrium". But at least I now know why I got too much vacuum and how to "solve" this theoretically.
5000 miles, this is what a 2002 Maxima spits out:
- Status
Similar threads
