Subaru 4EAT external trans filter cut open

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Nov 29, 2021
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There's nothing like cutting a transmission filter open, and the smell of fresh ATF, on your hands and all, in the morning. Maybe the Subaru community will also like these..

There is a LOT of discussion about how the black Tokyo Roki Subaru external trans filter cans ("AT oil," or Automatic Transmission oil as per Subaru) differ from a regular engine oil filter. I believe the main cited difference is bypass pressure, and it has been said you are not supposed to use an engine oil filter in place of one. @SubieRubyRoo once provided me information about how an engine oil filter is fine, with some NAPA/NAPA Gold acceptable alternatives, and why.. in the absence of this info (I lost it,) or if he cares to provide it again?again?, I purchased another OE Tokyo Roki filter and saved the previous one for a cut-open.

Should be noted that I've only seen Tokyo Roki as OE Subaru filter. This transmission, 4EAT, has external in earlier years and eventually went back to internal for some unknown reason in later years.

Here's that filter. Probably around 7000 to 10,000 miles on it, ballpark guess. Not original trans, miles unknown.

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Nice thick, heavy baseplate!

This is a well-made filter.

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Shots of media..
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@Trav Isn't the OE filter the higher bypass pressure? I dislike MrSubaru as a channel/presentation, would dissuade me from watching that.. thought the oil filter had lower bypass pressure or do I have that reversed. (I've never run an oil filter in place of a trans filter, FWIW. I've been given info that some think it is OK, i didnt act on that info.. I personally didn't trust it, however, always about learning something new, that's why phrasing it as I am.)

 
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I just replaced one on an 05, the shifts were a little harsh then I saw an oil filter on the trans, swapped it out for a $34 OE filter and the harshness was gone. The higher relief valve pressure seems to cause trouble, it also caused weepage (not a drip) at a hose connection that also cleared up. These are well documented symptoms of not using and OE, the OE is basically a bypass filter with no pressure relief valve.

 
The Wix website shows a 51365 filter for many Subie AT applications. That same filter is used on a bazillion other applications; mostly engines. The Fram website shows no filter for AT application. However the xref for the Wix becomes a Fram 6607 variant - used in a ton of engine applications. Both have a 9-11psi BP value.

I tried searching the OEM number (38325aa032) in many websites, and most came up empty. But when you xref the Wix number into those sites, you get the typical engine oil filter.

Filters don't know how they are being used. They only know sizes, burst ratings, media efficiency, BP values, etc. Using the proper atttributes will come up with a decent filter for xref. And you'll find most of them are broad applications.

The OEM AT filter (38325aa032) has no BP; just a big hole. That's not really a very good filter, in terms of filtering. But it makes sense why some people are reporting harsh shifts with other filters; it's likely the BP valve is altering the pressure ramping up into the valve body.
 
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The Wix website shows a 51365 filter for many Subie AT applications. That same filter is used on a bazillion other applications; mostly engines. The Fram website shows no filter for AT application. However the xref for the Wix becomes a Fram 6607 variant - used in a ton of engine applications. Both have a 9-11psi BP value.

I tried searching the OEM number (38325aa032) in many websites, and most came up empty. But when you xref the Wix number into those sites, you get the typical engine oil filter.

Filters don't know how they are being used. They only know sizes, burst ratings, media efficiency, BP values, etc. Using the proper atttributes will come up with a decent filter for xref. And you'll find most of them are broad applications.

The OEM AT filter (38325aa032) has no BP; just a big hole. That's not really a very good filter, in terms of filtering. But it makes sense why some people are reporting harsh shifts with other filters; it's likely the BP valve is altering the pressure ramping up into the valve body.
These filters were discontinued in late 07 and a block off plate installed. There is still a common rock catcher in the pan on cars that used it, may be that is the reason Subaru claims it is a life time filter because of the hole right through it.
 
Did you tear that filter open, or was it torn when you removed it? :unsure:

I know that Subaru says you only need to replace the filter if it's damaged. Was yours damaged before you removed it?
 
Did you tear that filter open, or was it torn when you removed it? :unsure:

I know that Subaru says you only need to replace the filter if it's damaged. Was yours damaged before you removed it?

No, not at all.

I've gotten into changing it on occasion. I can't help but think it is picking up some kind of crud from inside the trans, much like an engine oil filter does. Any cutting or tearing only happened when I opened it with my new filter cutter.

I find it shifts like 100% good.. do not know why Subaru would put it on the outside if they then said not to change it.. I only used OE..
 
I find it shifts like 100% good.. do not know why Subaru would put it on the outside if they then said not to change it.. I only used OE..
The reason is it acts as a bypass filter not a full flow filter only filtering 10% of the fluid going through it at any one time (a good thing IMO), there is no bypass valve in the filter just an open hole so even if were full with debris it would not restrict the flow much if any.
At 200K there is not much debris in them, some but no where near enough to clog it.

The downside to this was quick lube places didnt see the engine oil filter up there in the ring of fire and replaced the trans filter (despite the big white AT markings on the filter) with an engine oil filter. It happened more than one would think.
 
Just lost a whole post. OK let's make it again.. I think that is EJ253 with oil filter in exhaust manifold. My EJ251 it is hanging out in the middle of nowhere, you can run pretty much any oil filter you want on there that is thread compatible since bypass only comes in to play in limited instances and not that often... some EJs it's even on the top, I think (oil filter.) Though I do wonder if the oil filter on the trans was messing up pressures enough to affect shifts, sounds like it was...

I want to next try a Full oil filter since i found model numbers in a post from @slacktide_bitog https://bobistheoilguy.com/forums/threads/napa-has-full-oil-filters-at-a-good-price.356926/

Then again, I myself, I also use the drain plug (thank you Subaru! For putting one on) and change the ATF very frequently, reason is "Transmission are expensive, fluid is not." Subaru and some others call transmission fluid transmission oil. Shame on quick lube shops.
 

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