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What's the purpose of the "hole" at Oil Filter Base for Subaru Forester?


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If it doesn't seem to have any purpose and it's and depression rather than a hole maybe it's just something from the casting/machining i.e. to make it so a machine can handle the part or something like that.

 

interesting theory, well so many different theories so far about this.  It looks like pretty smooth and polished, so it must be with some purpose.

I cleaned that hole/depression, so at least I can confirm that it is depression without any leaking.  

Edited by drdavidzhang
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If it doesn't seem to have any purpose and it's and depression rather than a hole maybe it's just something from the casting/machining i.e. to make it so a machine can handle the part or something like that.

Exactly. I have a 2016 Outback so I know something about this. It's been discussed at Subaruoutback.org. This "hole" is simply an oval dimple about 2-3 mm deep. Mostly likely the result of the casting/machining process said above. I filled mine with JB Weld to get rid of the depression so that dirt and spilled oil don't get in there. Of course that's really not necessary. Any dirt there won't get into the engine with the filter in place. I changed the oil on this car a few days ago and the top-mounted filter is really easy to handle.

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There's some evidence online that a Toyota made similar to this has a nipple in a similar location. There are pics of an owner hanging a cup under the nipple to catch drips. Given Toyota's involvement with Subaru, maybe there was some crossover in tech - but fitting a nipple there was abandoned ?

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Here is a picture of the factory oil filter on the FB engine showing part of the hole. As I turned the filter very slowly and removed it, most of the oil in the filter drained down into the crankcase. There was very little oil left in the filter resulting in no spilled oil at all. The only oil left in the round aluminum tray at the base of the filter was on the mounting flange. Cleaning up was extremely easy, the easiest oil change I've ever done. I also installed a Fumoto valve shown in the 2nd pic.

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post-19332-0-04281700-1454631886_thumb.jpg

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There are many theories:
theory 1: a depression to collect sediment or residual oil when changing. this  depression keeps stuff from falling of flowing into the engine when you take the filter off.
 
theory 2: it's just something from the casting/machining i.e. to make it so a machine can handle the part or something like that. 
 
theory 3: subaru's future high end car has a sensor inside this depression so that it can detect oil leak :]
 
theory 4: it is for a different kind of oil filter

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  • 3 weeks later...

 

 
There are many theories:
theory 1: a depression to collect sediment or residual oil when changing. this  depression keeps stuff from falling of flowing into the engine when you take the filter off.
 
theory 2: it's just something from the casting/machining i.e. to make it so a machine can handle the part or something like that. 
 
theory 3: subaru's future high end car has a sensor inside this depression so that it can detect oil leak :]
 
theory 4: it is for a different kind of oil filter

 

I talked to my dealer, and he referred this to the service manager. Here is the reply:
"Hello David,
 
No one seems to know for sure. Looking at it most say it is number 2.
"
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