I believe the WIX 57055 has that same bypass pressure relief as the OEM filters…

 

Which is what, if I may ask?

Never considered this aspect of buying oil filters before. How how to does one find out what that pressure relief pressure is for filters versus what the car requires?

 

IIRC, it’s in the 23-25 psi range.

 

Manufacturers list bypass pressure specs on their website.

Subaru spec for bypass pressure for EJ20, EJ25 and FA20 engines is 23.2 PSI. Everyone rounds this to 23.

There can be a very large variation in bypass pressure from manufacturer to manufacturer and even within a specific model one brand.

For example, when searching the Purolator website for a filter for a 2015 Forester XT with the FA20 (2.0 liter) engine, all of the filters in the search results are spec'd at 20 - 30 PSI.

With the exception of their Racing filter, all Fram filters for the same car are listed @ 9 - 15 PSI. This is too low for our cars and why I'll never use a Fram filter on my Forester.

 

Thanks. Do I understand this correctly? Ideally one wants the filter bypass pressure to match the engine oil pressure as close as possible. Not too low, not too high. If too low, the filter may go into bypass mode prematurely and possibly not filter dirty oil very well. If too high, the filter will not go into bypass soon enough and might clog with too much dirty oil reducing oil flow to the engine.
Looks like the number stamped in the metal on top of my '21 Forester engine is FB25. I wonder what that bypass pressure spec is.

 

@Oldguy2,

The FB25 is 23PSI. The Fram filters will not bypass anymore than other filters IMO. The only time a filter may go into bypass is with very very cold oil...like 0F. But even if it does bypass the end result is to get some unfiltered oil to the bearings for a very short period of time. Having a bypass in the low twenties may actually allow starvation of oil. But that is likely not a problem.

 

Bypass pressure is a differential pressure across the filter and independent of total system pressure. There is no reason to match it to system pressure. The oil flow rate to the engine is unchanged by the bypass setting. The ratio of filtered to unfiltered oil changes as the bypass opens.

Getting pretty far off topic.

 

@Oldguy2,

As stated by @boureesub , there is no need to match the filter's bypass pressure to actual engine oil pressure.

The bypass valve simply prevents the engine from running out of oil if the filter begins to clog. It can also help with oil that gets thicker when it is extremely cold but modern oils make this less of a problem than it used to be.

The pressure relief valve opens when the pressure differential between either side of the filter media gets high enough to open the relief spring. As an example:

• If a filter has a 20 PSI relief spring and the difference in pressure between the unfiltered and filtered side is actually 15 PSI then the relief valve will be closed and the filter media will not be bypassed.
• If the same filter with 20 PSI relief spring saw 25 PSI difference between the filtered and unfiltered side of the filter media then the relief valve will be open and oil will bypass the filter media.

Actually there is a range of pressures where the valve starts to open and is fully open. Its not instantaneous.

If you want to geek out on this stuff then check out BobIsTheOilGuy.com.

 

There is the worry that unfiltered oil will go into the oil passages.

I guess there is the chance if the pump has enough volume, that it might go into bypass at higher rpm, but the pump's bypass circuit might bleed off enough flow at that point. The restrictions in the system are not going to change.

The reason why you have increasing oil pressure is because the flow hits a ceiling pretty early. If the flow could increase proportionately to the rpm, the pressure would remain constant.

 

Thanks for the clarification guys. I mistakenly assumed the discussion about the Subaru oil filter bypass pressure was somehow related to the engine's oil pressure specification. My bad. Looks like it is more about the design and performance of the oil filter itself ... which probably goes a long way explaining why all the aftermarket oil filters fit so many different car engines. Even the much criticized Fram 7317 series filters that I could put on my '21 Forester boxer engine also fits my '16 Honda Pilot V6 vcm engine and my son's '18 CRV with it's 1.5L turbo engine ... not to mention the hundreds & hundreds of other auto makes & models listed in Fram's application chart. I get it now.

 

was somehow related to the engine's oil pressure specification

The oil pump bypass is what you were thinking of. It only limits how high the pressure can go, but that number can exceed the bypass spring pressure when it's really cold. Probably not as much as the old days, due to better viscosity modifiers and synthetic oil.

I don't know that they give an actual pressure specification, other than hot idle minimum pressure.

The general rule of thumb is 10 psi per 1000 rpm. Of course it varies from engine to engine and brand to brand.

But it's all good, it created a decent discussion!

 

I don't know if this observation helps or hurts the discussion so far, BUT ...

I couldn't help but notice the difference in two oil filters bypass valves that the MrSubaru1387 YouTube-guy showed when he compared the 15A to the new "emergency" Subaru replacement filter. For those of you who haven't seen that video he posted this week, he had a lot of good things to say about the replacement filter compared to the Subaru 15A filter. He didn't know the manufacturer of the replacement filter, but made several claims that the old 15A filter was a Fram. The interesting part came when he gave each filter's bypass valve the old finger pressure test. The 15A filter bypass valve was clearly very hard to move while the replacement filter bypass valve was noticeably easier to move with his finger. So while the 15A filter this guy took apart may walk, talk and quack like a Fram filter, it clearly did not have a low pressure Fram bypass valve in it. Yet Subaru went to the trouble of asking some other filter manufacturer to supply a replacement, even painting the can the same blue color but apparently not specifying the same higher pressure relief valve for it. If true, that seems ironic.

All that seems to validate to me what the others who responded to my earlier questions about bypass pressure have clarified, namely that it has as much to do with protecting the filter element as anything else. This is the 1st Subaru I've ever owned and have found people's focus on oil filter bypass pressure new & different. I've not seen that sort of discussion on other owners forums for the other car brands I've owned. I'm also due for my last free oil change at the dealer next month on my '21 Forester. To each his own, but I've come to the conclusion that if I stick to Subaru's recommended oil change intervals, I can probably install any oil filter and sleep well at night.

 

I've come to the conclusion that if I stick to Subaru's recommended oil change intervals, I can probably install any oil filter and sleep well at night.

Of course you can. I have used dozens of frams on 4 different subarus in the last 15 years. Never a problem. Subaru's lubrication is no different than any other manufacturer. My own personal opinion is that they do it in the hopes you buy subaru filters. If there were a problem with the bypass setting and subaru felt it would cause harm. They would need to supply filters free of charg. They don't sot must be no problem.

Lastly, Fram knows more about oil filtration than subaru engineers and just as much about oil systems. Fram would never risk billions of $$$ in lawsuits if they were not 101% confident that the #7317 Filter is fine in subarus.

So sleep well at night and use the superior filtering Fram Ultra or Titanium.

 

2011 - SH: Australian Ryco brand oil filter - oil filter bypass pressure doubled?

I have an SG with EJ engine and SH with FB engine. Using our Australian Ryco brand oil filter selector, over time, I found the oil filter type and bypass pressure has changed.

The SG uses a Z436 filter. Initially, the SH used the Z436 and indeed in my once only Subaru dealer oil change they used the Subaru equivalent of the Z436.

About say, two years ago I contact Ryco twice, and it was adamant the filter type for the SH had changed to Z87A saying Subaru had changed its filter type, not Ryco. The Z87A is slightly bigger in diameter and possibly height.

A few weeks back I found that Ryco had changed the filter type for the SH again to Z1155. I contacted Ryco twice with the reply that it was a Subaru decision.

However, they did say that the bypass pressure valve setting for the Z436 & Z87A was 100kpa / 14.5psi but the bypass pressure for the Z1155 was 200kpa / 29psi.

Does anyone know about this change to double the bypass pressure? I presume either Subaru want to reduce wear or have found that possibly the engine requires more pressure at idle.

 

Note that the question here is:

Does anyone know about this change to double the bypass pressure?

(for the SH)

Stay on topic please

 

@PeterfromOz

Seems there has not been a doubling of the spec as earlier in this thread the pressures are quoted as:

The FB25 is 23PSI.

Subaru spec for bypass pressure for EJ20, EJ25 and FA20 engines is 23.2 PSI.

all of the filters in the search results are spec'd at 20 - 30 PSI.

Maybe this is the change: https://www.subaruforester.org/threads/another-subaru-oil-filter-change.849902/

 

I am using 15208AA100 (made in Japan) last 10 years and I never lost a drop of oil. I never had to add an oil too.