Question About Bypass Pressure

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My 2014 Impreza has an oil pressure in the 18 psi range. Does this mean that if I don't put in a filter with a bypass pressure in that range that a great deal of my oil will not go through the filter? Many of the on the shelf filters are in the 9 psi range. I currently use a Wix but I am curious what would happen if I switched. Would appreciate any comments.
 
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I believe that the bypass pressure refers to the differential across the filter itself that would lead to a bypass, not to the pressure of your system itself. As long as the filter is flowing freely, you will not have a bypass situation even if the system pressure is well over the bypass pressure rating. That said, I also have a 2014 Subaru and am more comfortable using oil filters that meet the higher bypass pressure that Subaru specifies.
 
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Think of they bypass as an "emergency relief poppet valve like you would see on your water heater and hydronic boiler ( and pressure cooker) Your Impreza oil pressure most likely can be as high as 50-60+ PSIG above 3000RPM. OE Subaru filters have a bypass above 20psid for filtered turbo oiling. Just purchase the (Fram built to high spec) "Subaru" service filter from the dealer - its the best bet for that car. Ive owned over 6 subarus over the years; The early cars (1.8L TBI in Loyale) did not use a bypass equipped filter. IIRC bypass valve was in filter bracket mount assy. Ive tried Purolator classic and various wix and none worked as I liked.
 
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All else being equal, a higher bypass rating will direct more oil through the filter media at a “cost” of reduced downstream pressure as the filter media is loaded with debris. But under most operating conditions (engine warm and filter free of excessive debris) there will be no significant performance difference between filters with different bypass pressure ratings.
 

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As others have said, the filter's bypass valve setting has nothing to do with the indicated engine oil pressure. The bypass valve is there to protect the filter from damage caused by too much pressure difference across the media if it gets clogged up. The bypass valve also ensures oil still gets to the engine by going through the bypass valve when the filter gets severely clogged. Of course any oil going through the bypass valve will be unfiltered, but unfiltered oil is better than no oil at all.
 
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Originally Posted By: ARCOgraphite
Think of they bypass as an "emergency relief poppet valve like you would see on your water heater and hydronic boiler ( and pressure cooker) Your Impreza oil pressure most likely can be as high as 50-60+ PSIG above 3000RPM. OE Subaru filters have a bypass above 20psid for filtered turbo oiling. Just purchase the (Fram built to high spec) "Subaru" service filter from the dealer - its the best bet for that car. Ive owned over 6 subarus over the years; The early cars (1.8L TBI in Loyale) did not use a bypass equipped filter. IIRC bypass valve was in filter bracket mount assy. Ive tried Purolator classic and various wix and none worked as I liked.
I've been these Subaru branded Tokyo Roki filters (listed as for the WRX) in quantity since the shipping cost doesn't go up much as you add filters. These are more similar to the filters than Subarus come from Japan with than the US blue cans and I have been very pleased with them. They look funny because they are short and wide, but those who have cut them open report that they have plenty of media area. http://www.amazon.com/gp/product/B00LD1J...ailpage_o03_s00 Never had any trouble with the blue cans, just didn't like them because they felt flimsy to me. It may have been Arco who warned me about the seals on the WIX filters and I ignored the advice, the first one I used allowed oil to seep out...lesson learned.
 
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I think that the Wix are the best constructed filter for Subarus right now. I use the WIX/Napa Gold 57055 on both my '99 and '14 Outback. Never an issue. Now, if you go with the lesser 27055 version, those seem to have a few more issues. If I remember correctly, the Tokyo Roki had issues not to long back about not actually meeting the bypass specs they claimed. They were coming in about 10-20% short. In addition, the FRAM/Honeywell-style Blue Subaru filter has some really low effiency. I think it was 96.5% at 40 microns. "Fine" but I prefer the Wix.
 
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