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Oil Pressure testing different oil filters (MD356000)
Conclusion: Oil filter sizing doesn't effect the pressure loss when the filter is new.
I've done some oil filter pressure testing (PSID) on my setup.
I'm using a remote oil filter (relocation kit) which I can change between M20x1.5 and 3/4-16" threads.
Oil is 0W40 Motul 8100, full synthetic.
Ignore any oil pressure section's where it's wavey - that's my Mivec moving causing the pressure to shift slightly.
*Note - 20kpa is 2.9psi.
100kpa is 14.5psi.
Sensor locations
OEM MD356000 Oil Filter. Cold Startup data OEM MD356000 Oil Filter. Normal oil temp, high rpm data. Wix 51515XP Oil Filter. Cold Startup data Wix 51515XP Oil Filter. Normal oil temp, high rpm data.
Physical size of the oil filters. Wix 51515 (non XP version) has almost triple the surface area of the Mitsubishi MD356000 filter.
Actual pictures of my oil filter relocation setup with sensors
So....
This was a bit of a fizz.
Nothing really happened - no massive change in pressures like I was expecting.
We're not even close to opening the bypass on either of these filters.
There is info all over the internet saying that the bypass opens when the oil is cold. My setup isn't even close to this.
My conclusion - run whatever size filter that you want that has the best efficiency.
Construction and reliability is far more important than surface area of media *WHEN NEW*.
The bypass is almost always open. The difference you are seeing between channel 1 and 2 is the bypass valve spring pressure. When the filter media creates an >~15psi pressure drop the valve opens. If you wanted to test how much oil the filter media can actually flow you would need to block the bypass and observe the pressure drop. I could be wrong though, I'm no fluid dynamics expert or anything.
Either way I think it's cool what you are up to, testing this stuff out.
The bypass is almost always open. The difference you are seeing between channel 1 and 2 is the bypass valve spring pressure. When the filter media creates an >~15psi pressure drop the valve opens. If you wanted to test how much oil the filter media can actually flow you would need to block the bypass and observe the pressure drop. I could be wrong though, I'm no fluid dynamics expert or anything.
Either way I think it's cool what you are up to, testing this stuff out.
The difference is pressure between CH1 and CH2 is the PSID across the oil filter.
20kpa is 3psi.
3psi is not enough to open a bypass valve.
The difference is pressure between CH1 and CH2 is the PSID across the oil filter.
20kpa is 3psi.
3psi is not enough to open a bypass valve.
It's your thread, I'm not gonna try and argue with you. I will say that as flow increases you should see an increase in pressure drop as the media can only flow so much.
It's your thread, I'm not gonna try and argue with you. I will say that as flow increases you should see an increase in pressure drop as the media can only flow so much.
Please, argue with me. I encourage it.
What you're saying is exactly what everyone else on the internet says.
That the bypass is open when the oil is cold.
I'm showing you with data that the bypass is not open.
My next test i'm doing is with a 30psi bypass Wix 51191 (https://www.wixfilters.com/Lookup/Pa...px?Part=186378)
What you're saying is exactly what everyone else on the internet says.
That the bypass is open when the oil is cold.
I'm showing you with data that the bypass is not open.
My next test i'm doing is with a 30psi bypass Wix 51191 (https://www.wixfilters.com/Lookup/Pa...px?Part=186378)
Ok sure
What you are showing is the pressure drop between the input of the filter and the output. That pressure drop is exactly what the bypass valve is regulating. Which is why the input tracks so well with the output pressure. If it wasn't bypassing or regulating what you would see is the pressure drop on the output increase as flow increased. Because the media would become more restrictive as flow increases.
I'm not saying its open when its cold, im saying its almost always open. The bypass is a regulator that flows as much oil through the media as it can and bypasses the rest so that the engine doesn't suffer damage from oil starvation. As the media gets dirty its resistance to flow increases and the bypass will just bypass more oil to keep the pressure drop to the engine regulated.
I think people have this notion that every drop of oil is being filtered as it makes its trip through the engine. That's just not the case, some oil is always moving through the filter media (unless its totally clogged) but most of the oil is being bypassed.
Last edited by Biggiesacks; May 25, 2021 at 03:25 PM.
What you are showing is the pressure drop between the input of the filter and the output. That pressure drop is exactly what the bypass valve is regulating. Which is why the input tracks so well with the output pressure. If it wasn't bypassing or regulating what you would see is the pressure drop on the output increase as flow increased. Because the media would become more restrictive as flow increases.
I'm not saying its open when its cold, im saying its almost always open. The bypass is a regulator that flows as much oil through the media as it can and bypasses the rest so that the engine doesn't suffer damage from oil starvation. As the media gets dirty its resistance to flow increases and the bypass will just bypass more oil to keep the pressure drop to the engine regulated.
You know how a pressure regulator works right?
It needs to reach that pressure before the valve will open.
If both the Wix 51515XP and the Mitsubishi MD356000 filters both open their bypass valves at 3psi, I would be very worried.
You're assuming too much.
You're assuming that the new filter media is quite restrictive, so as oil flows through the media increases then the pressure differential should increase.
This is what I thought too. But then I did the test and looked at the result.
New filter media looks to be *near zero* restriction.
The pressure differential over the oil filter is probably more to do with the flow angle changes made by the oil than the media itself.
If I did a test with a non-bypass oil filter, would that satisfy you?
You know how a pressure regulator works right?
It needs to reach that pressure before the valve will open.
If both the Wix 51515XP and the Mitsubishi MD356000 filters both open their bypass valves at 3psi, I would be very worried.
You're assuming too much.
You're assuming that the new filter media is quite restrictive, so as oil flows through the media increases then the pressure differential should increase.
This is what I thought too. But then I did the test and looked at the result.
New filter media looks to be *near zero* restriction.
The pressure differential over the oil filter is probably more to do with the flow angle changes made by the oil than the media itself.
If I did a test with a non-bypass oil filter, would that satisfy you?
I've never measured how much pressure it takes to open the bypass, I think that's what you have done here. If it's 3psi...well that's what it is I guess. I wouldn't be worried by that. It's what ever the filter media can handle. It's a paper filter, you can't just blast 150 or what ever psi worth of oil flow through it.
Last edited by Biggiesacks; May 25, 2021 at 05:49 PM.
In this instance the bypass is regulating the pressure across (or through) the filter media. It works off the pressure differential between the input and output sides of the filter media. If the filter media creates a flow restriction that causes a > spring pressure amount of force it will open the bypass allowing oil to flow around the filter media and fill up the output side of the filter. Looking from outside the filter you would only ever expect to see at most a spring pressure amount of pressure drop through the filter. The input and output sides of the filter are both pressurized, so it's not about when the engine oil pressure hits spring pressure, its about when the pressure differential inside the filter, across the media hits spring pressure.
Last edited by Biggiesacks; May 25, 2021 at 05:49 PM.
In this instance the bypass is regulating the pressure across (or through) the filter media. It works off the pressure differential between the input and output sides of the filter media. If the filter media creates a flow restriction that causes a > spring pressure amount of force it will open the bypass allowing oil to flow around the filter media and fill up the output side of the filter. Looking from outside the filter you would only ever expect to see at most a spring pressure amount of pressure drop through the filter. The input and output sides of the filter are both pressurized, so it's not about when the engine oil pressure hits spring pressure, its about when the pressure differential inside the filter, across the media hits spring pressure.
Yup, I understand all that.
Do you think a filter with a bypass pressure of 8-11 psi (Wix 51515xp) should open at 3psi?
Yup, I understand all that.
Do you think a filter with a bypass pressure of 8-11 psi (Wix 51515xp) should open at 3psi?
I don't know. It could be all kinds of different reasons. Clearly I haven't convinced you. You asked me what It would take for me though. I would need to see data sheets. From what I know about filters, there is no way I believe these oil filters can flow anything close to what the oil pump is putting out. I'm sure there are filters that can, they are either way bigger or filter way less.
The difference is pressure between CH1 and CH2 is the PSID across the oil filter.
20kpa is 3psi.
3psi is not enough to open a bypass valve.
Correct, it is the pressure differential which allows the bypass to initiate so if the pressure differential never gets anywhere near the spring pressure then the bypass is not opening. However, what I have struggled to find is whether or not the spring rating was for crack pressure of for full bypass. If you take a wastegate as an example, a 15psi wastegate actuator will hold boost to 15psi because at that pressure it is fully open. However, around 11-12psi you will experience crack pressure, which is the point the spring initiates movement. I can see this when I compare boost response on just wastegate pressure vs 100% WGDC.
Therefore, if we assume the spring pressure ratings are based on full bypass, I would expect a 15psi bypass rating to have a crack pressure of 10-12psi. Whether or not that crack pressure is enough to instantly reduce the pressure on the backside of the filter is unknown. Based on your data showing the pressure differential never exceeds 3psi, the bypass is not opening.
Also, the XP filters are designed for extended mileage so they do this by running less surface area because they back it with steel mesh and they reduce the micron rating to 35u absolute. What is interesting is that when I was calling about filter options for the GTR, WIX said they changed suppliers for some of their media and the standard WIX filters have a rating of 21u absolute. If you look at WIX 51568 (21u & 16psi bypass), it has a surface area of 1142cm2 so a good option for the EVO, but it is significantly longer. I run this on my GTR and have one for my next EVO oil change. Below is the WIX 57092 vs WIX 51568.
the fact that it never exceeds X psi is proof to me that it is being regulated. As flow increases back pressure should also increase.
As I said there any number of reasons that filter could have such a low bypass. Do we even have data from the mfg for what the bypass pressure should be? This filter could be faulty etc..
Last edited by Biggiesacks; May 26, 2021 at 12:39 PM.
the fact that it never exceeds X psi is proof to me that it is being regulated. As flow increases back pressure should also increase.
As I said there any number of reasons that filter could have such a low bypass. Do we even have data from the mfg for what the bypass pressure should be? This filter could be faulty etc..
Dont worry - i'll collect some data from the non-bypass filter soon. Just waiting on some other parts to arrive.
I think we'll all be surprised!
May 25, 2021, 01:52 PM
