Adapter for different oil filter thread sizes?


It's been difficult finding a really good oil filter for my car since Subaru engineers are a bunch of weirdos, and I'm kind of a perfectionist. My car has a very high flow oil pump and specs a small filter with a bypass rating of 23 psi. I'm currently using an oversized Baldwin filter with a bypass rating of 20psi. The Baldwin is probably better than stock in terms of not going into bypass as easily (due to the large size), but it's not very efficient, 99% at 40 micron. This is probably a lot worse than the OEM filter, which is either a Fram Extraguard or Toughguard (not sure).

I'm looking for a filter that will not bypass much more easily than stock, but also has high efficiency. I like the Fram Ultra, but its bypass rating in any compatible filter is only 12 psi, and there are no filters in a M20x1.5 thread size that are much larger than stock (less restriction to compensate for the lower bypass rating). I've found the perfect filter, though, a FRAM XG10575. It's got 45% more filter volume than stock, a 22psi bypass, and 20 micron absolute efficiency. Perfect. I'm in love. I don't even care that it's a bit too tall, since the Baldwin has already burned a hole through my hood insulation. The real problem is that my M20x1.5 male nub is too small for her M22x1.5 female opening. Are there any M20 to M22 adapters I could use to accommodate an M22x1.5 filter?
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The right way to do this would be to have a machine shop make an new filter mounting "spud" that screws exactly the same onto the engine, but has the M22x1.5 threads on the filter side. I doubt anyone makes one for sale, but maybe they do if you search long enough.
Pittsburgh,PA U.S.A.
It sounds like a Helicoil would work in that application. However I looked on McMaster Carr web site of there Helicoils and there is not one made for that fine a thread at that big a size, and the space between the inner and outer is also not enough. If there is no Helicoil made for those two sizes, it very will may be that there is not enough space between the inner and outer diameters, and it that is so, then it can not be done. But for a final check give the manufactures of Helicoil a phone call.

Getting a machine shop go make a new mount with the proper threads sounds like a great way to do it. Also the link above with one of the filter adapters on the bottom of the link, connected to the first item in that link via two hoses looks like it would also work.

I would guess that getting a machine shop to make the custom mount part will run you about $300.00 to $400.00 but you might get lucky and find a shop willing to make it for much less. That would be a great little project for a skilled machinist student to make at a school that is teaching machining. And if you found a school who had a student that would make it, you might get it made real cheap.

Another option would be a private machinist with a shop in there house. There are people who have a shop in there house for a hobby.


Site Donor 2021
Did a quick search on the Wix page for the threads and bypass you mentioned. Not sure what size filter you are looking for but all of the dimensions are on the list. See if anything is close then cross reference if you prefer another brand.

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