How often does the bypass valve activate

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Assuming I have a new oil filter with 0W-30 engine oil. Does the bypass valve always activate if I were to go into the upper rev ranges or does it only start to happen when the filter is clogged?
 
if functioning correctly the BPV has a threshold of pressure. Exceed a certain value and it is activated.

Some oil still goes through the filter.

This is why a regular oil filter can never be very good. It simply must pass too much oil.
 
Been trying to understand if this is more of a cold flow or a hot flow issue - and I am still unsure but now leaning more to the hot bypass at high RPM. Remember this is a differential pressure, the engine is quite a resistance to flow, so typically the loggerhead is the spill out at the mains. This bearing "leakage" resistor is reduced when hot, putting the filter more in the circuit forefront of the premier resistor to mass flow. If worried, you'll find the WIX typ utilise a bypass at the base plate which will not wash the media in bypass. Alternatively, Some racers use a large mesh medium to insure there is some impedance to low flying birds and other flotsam. Recall flow is in thru annular ring of holes and to the main gallies out through the centre.
 
Does anybody really know,can you see inside your filter?

i think tho only on cold start ups and high rpms before oil comes to temp and with thick 20w50 oil say.

thats why i always run over sized filters on my stuff,to try an "ease" the restriction of oil flow.
 
Originally Posted By: takax2040
Assuming I have a new oil filter with 0W-30 engine oil. Does the bypass valve always activate if I were to go into the upper rev ranges or does it only start to happen when the filter is clogged?


You'll get different views here. My observations show that it's mostly a function of oil pump relief action. They work in concert. More relief flow, more PSID. It doesn't necessarily mean the bypass opens ..just elevated PSID. As the full pump output "fits" through the engine, the PSID retreats. If you're pegged on starting pressure, you may be at elevated PSID.

High volume is another possibility. It's never been on my radar ..since high rpm with high volume isn't anywhere near as common as millions of cold starts.

Loading will exacerbate and elongate the condition. It still retreats to very little PSID after warm up. You're effectively using a smaller filter so the reactive appearance of visc is more pronounced. Whether new or with some mileage on it, at full warm up at most sensible volumes 2PSID or less would be not uncommon.
 
Oh I see so as the oil warms to temperature. The flow through the engine will be faster so there will be greater pressure differential at the filter. When fully warmed up the oil will also thin thereby reducing the pressure differential.
Why I'm asking this is because I was wondering the effects of prolonged hill climbing on engine oil flow and filtration. As in sustained 2 hours of 4000-5000 rpm operation at 1/2 throttle to full throttle. Will this result in the bypass valve opening and thus allow unfiltered oil into the engine.
I am using a standard sized OEM filter. not many choices of filters where I stay.
The relief valve I have roughly tested to open at 16 psi pressure differential.
 
Originally Posted By: Gary Allan

You'll get different views here. My observations show that it's mostly a function of oil pump relief action. They work in concert. More relief flow, more PSID. It doesn't necessarily mean the bypass opens ..just elevated PSID. As the full pump output "fits" through the engine, the PSID retreats. If you're pegged on starting pressure, you may be at elevated PSID.

High volume is another possibility. It's never been on my radar ..since high rpm with high volume isn't anywhere near as common as millions of cold starts.

Loading will exacerbate and elongate the condition. It still retreats to very little PSID after warm up. You're effectively using a smaller filter so the reactive appearance of visc is more pronounced. Whether new or with some mileage on it, at full warm up at most sensible volumes 2PSID or less would be not uncommon.


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One of the best summaries I've read on the subject.

FWIW, some engines dump the oil released through the pressure relief valve back into the oil pump intake rather than back into the pan, which at least means that once a piece of grit is picked up out of the pan it will eventually go through the filter before going anywhere else. The downside being that the same piece of grit might run through the oil pump several times before finally going through the filter... pick your poison.
 
Quote:
Oh I see so as the oil warms to temperature. The flow through the engine will be faster so there will be greater pressure differential at the filter.


Not quite. You've got some altered views when a pump is in relief as opposed when the full output is a singular, unified flow. It can get complicated in concept.

It basically boils down to a given attenuated pressure (the relief setting) and the product of the given flow through the engine ..which will be a % of that attenuated pressure.

The filter will see the attenuated pressure above it (it's now a parallel circuit from this end with applied pressure and divergent flow) ..and the developed pressure below it ( volume through a restriction resistance). That's what gives you PSID in relief. As the divergent flow transitions to a single, unified flow ..the developed pressure will rise toward the pressure limit. The PSID will retreat. You need to massage that view where you have a volume/viscosity combo that makes maintaining the pressure limit ..but it should be easily adaptable on a sliding scale.

A filter, any filter, is statically of high resistance to flow. Try pouring oil in one at room temperature. It's only when it's seeing much greater "back pressure" on the interior centerwell where this true resistance is minimalized due to the comparative restriction of the engine.

You will ultimately reach throughput limits at ultra high volume. For most, that's never a problem.
 
Hi Gary,
I've been meaning to research a bit more on the operation of an oil pump and some oil fluid dynamics so I can understand you and (Superbusa) better. But do you have any visuals that describe the pump relief and what that means? I'm assuming this is a completely separate concept from the filter. So if the oil pump is being pushed too hard and it can't seem to pump the oil fast enough (ie the pressure rises too high...the engine can't use the oil as fast as the engine is TRYING to make the oil pump, pump it), there is a relief valve that diverts some of the oil on the high pressure side of the pump either back into the sump or back into the flow volume on the vacuum/low pressure side? And then, I'm still confused on how this concept meshes with the oil filter bypass.

Also, when you guys say PSID, is that an acronym or is that just pounds per square inch differential across a boundary? (we call that delta P across a boundary so it is non discriminating on units of pressure :) ).

Anyway, some reference reading/diagrams would be helpful.
 
^P is acceptable nomenclature ..but I'd tend to use it where change occurs over flow or time. Remember, I'm undisciplined.

The pump (ignoring any inherent efficiency issues - ie pump losses) the output is mostly linear and irresistible. There are other alterations to the view ..such as internal pump resistance ..where the inlet port and the outlet port will limit things. These are fringe factors for the MEAT of functions.

Quote:
But do you have any visuals that describe the pump relief and what that means? I'm assuming this is a completely separate concept from the filter.


The problem we all have is in transitioning views from compartmentalized/isolated elements ..and applying altered physics upon them.

We can take a standard resistive series circuit and see, quite easily, that the pressures developed due to current flow will be in ratio to each other. We'll also, in common sense concession ..even without bona fide observation, reason that if we're seeing 80lb at the gauge ..and have an 85lb relief, AND have a down stream sender ..that we're NOT seeing any significant ^P across the filter. This is just for suggested rational "proof" so that we can continue on in the discussion. If we get hung up here ..then this is where we'll stay.

..but assuming you're with me ..and accept this very common sense given (we're out of relief), we, again, in the compartmentalized/isolated format, we will continue to see the engine, in isolation (and at all times) will be a resistive element. The pressure above it will be a product of the flow @ visc. Now this will always be the case. The flow or the visc may vary ..so it may compress or expand how those two changing factors appear and evidence themselves ..but there is a flow:visc exchange that should work on either side of the = sign.

This you have to agree with for us to move on. I'll admit that pulling all the sub elements together here is not easy. Especially since I would love to find a better way to do it. Analogy usually works ..but is often rejected the more disciplined you are.

If you're still with me, we then transition from a series circuit to a parallel one. Before we were viewing a IxR=P with two resistive components, the filter and the engine ..with the engine being the bigger resistive load.

Two pathways ..one with a sub set (the engine) that will still be at IxR=P

Here's the struggle. Ignore visc for a moment. This confounds it since you sit there saying that if you can't fit it through at any ONE moment ..that you can't fit more of it without it lessening. Think of inertia. This is JUST to get the concept. This does work that way on a cold start (as in really cold) where a pump attempts to move a motionless non-Newtonian fluid and turn it into a Newtonian fluid. You can even look at it as a Power Factor conversion where the pressure applied is out of phase with the current flow.

So, the pump spins it's tires ..recirculating fluid internally while the pressure (and suction) applied gets the static column (both on the suction and outlet side) moving.

Now you may be able to see that the engine will show the product of IxR (up swinging as flow goes from zero to whatever it limits flow) The filter will see this near same number up to the point the engine stops accepting flow adn will continue on up to the max applied pressure.

There is your ^P across the filter. As the "phase" relationship of P applied and full flow become more aligned (a non-reactive, series flow), the ^P retreats. The engine "comes up" to (nearly) meet the applied pressure and the filter resumes being a non-factor as far as pressure alterations.

See if that injects enough stray concepts for you to relate to and "tie in".
 
Thanks for the V = IxR electrical analogy. That makes a lot more sense to me. I might have to open up the fluid mech/dynamics text for a refresher though.
 
Look at the filter as an orifice in a fluid circuit. Most of your laminar flow depictions will show it to be a choke. This is how they work. They also have impedance that isn't linear.

The reason I'm saying that is that you have to take the typical orifice physics and throw it out the window if you cut the relative flows to 1/10th of where the orifice is actually an impedance to flow vs. just a transitional change in velocity (from VERY slow to less VERY SLOW). All the lessons will probably demonstrate an orifice doing what an orifice usually does. The difference in our case is that the orifice is several times the cross section of the terminal restrictive element. It's not an orifice at all until it's either at very high volume, or not a series circuit with variable flow and resultant pressures.

Both images here show a partition The lower one is an orifice that impedes flow. The upper one is an orifice that does not.



The upper image here shows an orifice that does not impede flow, but evidences ^P across it. The lower image shows an orifice that does not (much).

 
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Several of the above posts are correct, and I want to agree with them and disagree about some others.

Starting at the oil pump, there is a relief valve that limits the pressure to the engine. It also limits the stress on the oil pump drive. The oil that bypasses there goes back to the pan.

There is a second bypass to protect the filter and assure flow usually in the filter, but GM has them in the engine. The oil that bypasses the filter there goes unfiltered to the engine. the higher the RPM and thicker the oil, the more likely one or the other bypass opens.

Somebody mentioned Wix has the bypass on the threaded end so the unfiltered oil doesn't wash over the dirty side of the filter before going to the bearings. True. So do many other better filters, the Clarcor brands, Champ Ecores, and Motorcraft. Fram, most Purolator products, and Champ non Ecores allow the oil to wash over the dirty filter element to the bypass at the dome end. Harmful? Like much else, guess work. Right now, I am looking for a cheap thread end filter to fit my truck. No sense running a dome end if you can buy a thread end for the same price.

The outside of a filter tells you very little about its flow rate or dirt holding capacity. In the past I have found Fram 3950's have 1/3 the the area of the same size AC PF 1177. It also tells you nothing about the quality of the media. Less of a better media shouldn't be a problem. Most of the other brands fell between them, but the recent Purolators I cut open were closer to the old Frams. I am going to be running and cutting open some other brands.
 
Originally Posted By: ARCOgraphite
Been trying to understand if this is more of a cold flow or a hot flow issue - and I am still unsure but now leaning more to the hot bypass at high RPM.


If the filter goes into bypass mode or not is dependant on 4 things: 1) The bypass valve setting (PSI), 2) The oil viscosity, 3) The oil pump's flow rate and 4) The filter media flow resistance factor.

Filter designers try to base the bypass valve setting on factors 2) thru 4).

So, as was discussed in painstakingly detail in the Subaru oil pump thread, if Subaru specifies a 23 psi bypass filter for a 12 gpm oil pumped engine, and someone puts on a filter that has a 8 psi bypass valve, then I'd say it's VERY possible that the filter is going into bypass at high RPM (ie, high oil pump volume) when the oil is fully hot.

Originally Posted By: ARCOgraphite
Remember this is a differential pressure, the engine is quite a resistance to flow, so typically the loggerhead is the spill out at the mains. This bearing "leakage" resistor is reduced when hot, putting the filter more in the circuit forefront of the premier resistor to mass flow.


The flow resistance created by the engine itself (as stated above), along with what the max oil pump pressure relief setting is (another important factor), will ultimately determine the max oil flow volume going through the filter/engine series circuit.

If an engine like Subaru has a 12 gpm oil pump, you can bet the flow circuit in the engine can flow that 12 gpm at some point, so that same flow rate must also go through the filter ... either fully through the filtering media, or split between the media and the bypass valve.

Yes, it's true that the most likely time the bypass valve will go open is under cold oil and high RPM conditions. If it was 20 deg F outside, and someone fired up and engine and revved it to 4000+ RPM you'd surely see the filter bypass open under conditions like that. The only time I'd worry about opening the bypass valve with hot oil is under high RPM conditions with a filter with a bypass setting much lower than specified for that vehicle.
 
Originally Posted By: takax2040
Oh I see so as the oil warms to temperature. The flow through the engine will be faster so there will be greater pressure differential at the filter. When fully warmed up the oil will also thin thereby reducing the pressure differential.


When fully warmed up, there will be more oil flow volume, BUT the viscosity is much thinner than when cold. You have to consider the effects of both viscosity and flow rate.

Cold Oil
Less volume - more PSID across filter because the viscosity is the stronger factor in the PSID than volume. Higher chance of bypass valve opening.

Hot Oil
More volume - less PSID across filter because the viscosity if a stronger factor in the PSID than volume. Less change of bypass valve opening.
 
Originally Posted By: 09rexwagon

I've been meaning to research a bit more on the operation of an oil pump and some oil fluid dynamics so I can understand you and (Superbusa) better. But do you have any visuals that describe the pump relief and what that means? I'm assuming this is a completely separate concept from the filter.


I think there were various threads where all this was hammered out ... you'll see that me and Gary have many points we don't seem to agree on. Could just be terminology ... don't care anymore, and I think Gary has me on "ignore" now, so he can't even see my postings anymore anyway.
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I'll see if I can find one thread where (member called chunky) made some nice schematics showing the oil system, etc.

Edit -- read this thread, and search for others. There are many similar threads out there that will make your head hurt ... mostly the ones where Gary and I are trying to agree on things. I'm sure you'll quickly figure out who makes more sense.
wink.gif


http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1519777&page=1

Originally Posted By: 09rexwagon
So if the oil pump is being pushed too hard and it can't seem to pump the oil fast enough (ie the pressure rises too high...the engine can't use the oil as fast as the engine is TRYING to make the oil pump, pump it), there is a relief valve that diverts some of the oil on the high pressure side of the pump either back into the sump or back into the flow volume on the vacuum/low pressure side? And then, I'm still confused on how this concept meshes with the oil filter bypass.


You are correct on the oil pump's pressure relief valve. It's meant to LIMIT the oil pressure the pump puts out to the engine. Say it's set to 80 psi ... that means the pump can only put 80 psi of pressure on the inlet of the filter/engine flow circuit. Well, imaging holding the supply pressure to 80 psi and varying the oil viscosity. You can see that less oil volume (GPM) can be pushed through the circuit at 80 psi when cold and thick than if the oil was warm and thin. If the oil gets thin enough, the pump will actual go out of pressure relief and the pump's output pressure will go below 80 psi. If you have an oil pressure gauge in you car you can see this happening as the oil warms up. You might see the gauge pegged at 70 psi at high RPM with cold oil, but only pegged at 60 psi at high RPM after the oil is hot. In this example, when the oil is hot the oil pump is not getting into pressure relief territory anymore, because the gauge is no longer indicating 70 psi. The delta between the pump's relief pressure of 80 and the gauge pressure of 70 when the pump is in relief is the PSID across the filter, as most oil pressure gauges are located between the filter and engine inlet.

Originally Posted By: 09rexwagon
Also, when you guys say PSID, is that an acronym or is that just pounds per square inch differential across a boundary? (we call that delta P across a boundary so it is non discriminating on units of pressure :) ).

Anyway, some reference reading/diagrams would be helpful.


Yes ... PSID means "pounds per square inch differential" ... meaning the "delta pressure" in PSI across the filter media.
 
Originally Posted By: SuperBusa
The delta between the pump's relief pressure of 80 and the gauge pressure of 70 when the pump is in relief is the PSID across the filter, as most oil pressure gauges are located between the filter and engine inlet.

Just for some clarification, when you say the deltaP (there I go :) ) across the filter you mean the difference in pressure slightly before the filter and the the pressure out of the middle outlet? Essentially the stimulus of whether the bypass valve is open or not? So in your example a filter with a 23psi bypass valve would still be firmly shut since the deltaP across the filter is only 10 psid. I'm assuming the maximum deltaP ever across a filter will be equal to approximately the filters bypass pressure given that when the bypass valve opens, the ability to flow is not as restricted so the guage pressure would not drop any lower?
 
Originally Posted By: 09rexwagon
Originally Posted By: SuperBusa
The delta between the pump's relief pressure of 80 and the gauge pressure of 70 when the pump is in relief is the PSID across the filter, as most oil pressure gauges are located between the filter and engine inlet.


Just for some clarification, when you say the deltaP (there I go :) ) across the filter you mean the difference in pressure slightly before the filter and the the pressure out of the middle outlet? Essentially the stimulus of whether the bypass valve is open or not?


Yes ... the PSID (ie, deltaP) is the pressure difference across the filter media ... which is the deltaP between the filter inlet vs. outlet. There is always some level of PSID across a filter when there is oil flow going through it. Basic fluids 101.

Originally Posted By: 09rexwagon
So in your example a filter with a 23psi bypass valve would still be firmly shut since the deltaP across the filter is only 10 psid.


Exactly. If a bypass valve is set to 23 psi, then it takes 23 delta PSI across the valve to make it start to open. Basic spring loaded valve mechanics.

Originally Posted By: 09rexwagon
I'm assuming the maximum deltaP ever across a filter will be equal to approximately the filters bypass pressure given that when the bypass valve opens, the ability to flow is not as restricted so the guage pressure would not drop any lower?


Yes, that's basically true. Although, keep in mind that the bypass valve is a spring loaded device, so a spring with a fixed spring constant will take slightly more pressure to make the vavle open farther and farther. So, what happens is the bypass valve will keep opening farther to increase bypass flow until the PSID stabilizes and no longer increasing. Most filters will spec a bypass setting something like X~Y (8~11 psi or 12~16 psi for example), which probably means they start to open at X psi and are fully open at Y psi.
 
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