final conclusion on using low bypass value filter

[Eugene_Von]

Hi folks, recently I bought a subaru and I found its standard oil filter bypass value is 23PSI, which is way higher then normal Mobile 1 or Fram utra filter.
So I did some research and my conclusion is: it's ok to use low bypass value filter, if its threshold flow rate is large enough.
why?
Bypass will take effect in some cases:
1.cold weather start, in which you really need some oil to circulate, I'm not gonna focus on this.
2.high rpm, in which engine saturate filter flow capacity and differential pressure builds up util hits bypass value

Let's assume now for German cars or subaru that their engine indeed push oil aggressively to filter, if filter's flow capacity is good enough to handle, then it will be fine because no differential pressure will be built up; as rpm grows, finally it will hit the threshold. So it's not just a number of bypass pressure, it's indeed a function between maximum flowrate capacity and bypass value.

So, let's use a methodology of extremecy. Suppose you have a really low value bypass filter but your flowrate is supreme (which is impossible) that it can handle any oil flow from the engine, then bypass valve will never be triggered. This is indeed the case when you don't have a filter at all. But on the other opposite, even you have a high bypass filter (say 23) but flowrate maximum is easily reached, it will be the same as is only 5...

Please correct me if I'm wrong

 

[FowVay]

Eugene, this is why the bypass valve setting is referred to as being a differential pressure setting. The filter will have to have a differential between the incoming and outgoing volumes of fluid in order to develop any sort of pressure differential.

 

[Linctex]

Read all about it here:

https://bobistheoilguy.com/forums/ubbthreads.php/topics/3197094/

 

[Eugene_Von]

But I cannot read this picture, it shows for PSID from 0 to some value its flow rate varies, how could this happen? PSID should be a flat curve (normal pressure drop) if incoming pressure does not reach max flow rate and keep increasing until hits the bypass value.

 

[Linctex]

I honestly wouldn't worry about it.

The bypass feature of an oil filter is so SELDOM used (usually high RPM with cold oil) that you can just about guarantee it'll never go into bypass if you are mindful of your driving habits.

 

[Linctex]

That chart goes up to "10 gpm".

It's not realistic... try to fill two 5-gallon pails in 60 seconds with a garden hose.

IF you *can* find a faucet and hose that flows that much (usually you need small fire hose)...imagine that kind of flow in an engine! You'd empty a 4-quart (1 gallon) oil pan every 6 seconds!!!

It is NOT a realistic graph - it's for educational purposes only and doesn't apply to 100% of the passenger cars and light trucks out there (though some race cars may use this info).

 

[Linctex]

Also, make sure you understand the difference between the bypass in the filter, and the pressure bypass in the oil pump.

Even if an oil pump is capable of high GPM, it almost never pushes that much oil through the parts of an engine (tight clearances). That's why the oil pump has a high-pressure bypass built into it.

If, by some chance you were driving down the highway and some HUGE oil leak occurred (lost the entire oil pressure sending unit, or an oil gallery plug) - then oil FLOW (not pressure, because you just lost all of it) might push the filter bypass open, but not otherwise.

 

[Gokhan]

As long as the oil filter has a bypass valve and it's not leaking but opening when needed, I wouldn't worry about it.

As far as I understand, the pressure setting for the bypass valve is dictated by the oil-filter construction. It's not an engine-dependent spec. Larger filters have lower settings because they have lower Delta P (pressure difference) values (less resistance to oil flow). Also, larger the area is higher the force is for a given pressure.

The only function of the bypass valve is to protect the oil filter and the setting is determined by the oil-filter manufacturer so that the oil filter isn't damaged or doesn't burst. Again, it's not an engine- or application-dependent spec and it shouldn't be a concern while choosing an oil filter.

 

[goodtimes]

Yet few if any discuss the size of the bypass valve as a limiting factor to flow. Look at the Ecogard posted recently here. That tiny bypass hole is not for me, just looking at it without any measurements. Regardless the spring pressure setting when it opens, when it does it ought to flow close to equaling the outlet pipe hole.

 

[ZeeOSix]

Originally Posted By: Eugene_Von


But I cannot read this picture, it shows for PSID from 0 to some value its flow rate varies, how could this happen? PSID should be a flat curve (normal pressure drop) if incoming pressure does not reach max flow rate and keep increasing until hits the bypass value.


The graph is showing the delta-p across the filters as a function of flow rate. Obviously, these are filters without a bypass valve, so the bypass valve is out of the picture on this graph. Also, these curves are for cold thick oil; that's why the delta-p is so high with low flow rates.

This is what a typical good flowing oil filter would look like with thin hot oil flowing through it.

 

[ZeeOSix]

Originally Posted By: Linctex
Even if an oil pump is capable of high GPM, it almost never pushes that much oil through the parts of an engine (tight clearances). That's why the oil pump has a high-pressure bypass built into it.


High performance engines certainly can get 10~12 GPM of flow going through them before the oil pump hits pressure relief (usually 80~90 PSI). With thin hot oil, the pressure drop across the whole oiling system is much lower with high flow rates.

 

[ZeeOSix]

Originally Posted By: Linctex
If, by some chance you were driving down the highway and some HUGE oil leak occurred (lost the entire oil pressure sending unit, or an oil gallery plug) - then oil FLOW (not pressure, because you just lost all of it) might push the filter bypass open, but not otherwise.


Not sure what you're envisioning there. If a major leak occurred in the oiling system the flow coming out the oil pump would remain the same but the oil pressure would drop drastically (filter bypass wouldn't open or do anything) until all the oil leaked out of the system ... then the oil pressure would go to zero and the engine would get toasted from lack of oil.

 

[ZeeOSix]

Originally Posted By: Gokhan
As far as I understand, the pressure setting for the bypass valve is dictated by the oil-filter construction. It's not an engine-dependent spec.


It is in terms of engine oil pump max volumetric flow and also specified oil weight. But yes, the filter construction and flow resistance of the media is also factored into the bypass valve setting.