Subaru Forester Owners Forum banner

1 - 20 of 21 Posts

·
Registered
Joined
·
81 Posts
Discussion Starter · #1 ·
I got a nice Used 2003 Forester XS Premium, 52K miles, in the middle of January. I went to the auto parts store to buy a new oil filter and noticed the size of the filter was this tiny little filter large enough for a lawn mower engine. How can this filter provide all the filtering for this engine. Also such a small filter can cause back pressure at higher RPMs to cause the pressure bypass (in most engines) to bypass oil that's not filtered into the oil gallies.

Can I fit a larger filter to the engine? If so what is the part, and if not why not?
I read about this trick on a site called "The Engine Oil Bible" http://www.chris-longhurst.com/carbibles/engineoil_bible.html Scroll down near bottom "Larger filters on standard cars?"
:shock:
 

·
Mr. April 2008, Image Master
2005 X
Joined
·
1,325 Posts
There's a school of thought which says that enlarging the oil filter on your car is A Good Thing. Why is this?
The small oil filters fitted to engines these days run with quite a high back pressure, and the bypass valve trips at about 3500rpm.
Remember that.

If you increase the size of the filter, this will raise the rpm at which the bypass valve will switch
. With a bigger filter and lower back pressure, for the same rpm (prior to bypass valve operation) less engine power will be lost in the filter. Bigger filter means better filtering and more power at low to mid revs.
I don't understand how the bypass valve that "trips" at 35k rpm will do so later (or higher rpm) just because you are using a larger filter... Wouldn't that mean it'd be pressure sensitive rather then rpm?

 

·
The Modfather
2019 Impreza 5dr Sport - Manual
Joined
·
8,070 Posts
The size of the filter is not the only thing that determines how well it works. It's the filter media. The smaller SOA filter actually has more dirt holding ability due to what the material is made out of. I've been using the "smaller" filters and have had an oil analysis done and it looks fine.

the bypass valve that "trips" at 35K rpm
That aint the only thing that will trip at that many RPM's :tongue:

I have some filter sizes here: http://www.scoobymods.com/forums/showthread.php?t=3014
 

·
Registered
Joined
·
81 Posts
Discussion Starter · #4 ·
Larger Filters

The Wraith said:
I don't understand how the bypass valve that "trips" at 35k rpm will do so later (or higher rpm) just because you are using a larger filter... Wouldn't that mean it'd be pressure sensitive rather then rpm?


Larger filter equals more surface area which equals less back pressure.

Peaty, or Anyone:

I read the Scoobymods column. I am new to Subaru, what is H4 and H6? I see that the H6 filter has a larger diameter therefore a larger filter. Is there any difference between say a Fram filter with a back flow valve and a Subaru filter part number 15208AA100 ? Why should I use a Subaru Filter or not?
 

·
Registered
2006 Forester
Joined
·
174 Posts
The media and construction are the important things; not the size. In fact, some larger oil filters by the same manufacturer performed less well than their smaller counterparts. Don't worry about the smaller size- really!
 

·
The Modfather
2019 Impreza 5dr Sport - Manual
Joined
·
8,070 Posts
H4 = Flat 4 motor H6 = Flat 6 cylinder motor

Subaru has gone to two filter's the 4 and 6 filter mostly because it's easier that way. The smaller filter only fits on the Turbo motor due to size issues, the H6 filter will fit on the NA (non Turbo) motor. The thing is, for me, I change the oil every 3-4k anyway so I want good filtering capability, I don't worry all that much about how long it will take to get dirty and bypass. I don't wait that long. Subaru filters are made by purolator again AFAIK
 

·
Registered
2017 Forester 2.5I - 6 Speed
Joined
·
994 Posts
When I get my oil changed at the Sub dealer. Will I always get a genuine Subaru filter?
 

·
Premium Member
Joined
·
261 Posts
That's not what she said !!!!!!!!!!!!!!!!!! Anyway Subaru engineers know what is needed for their engines and what volume, what media, what pressure relief setting etc. I'm sure they spec an oil filter that has a large safety margin. Why we keep trying to be mechanical and lubracation engineers and out guess the factory data and recomendations is not too smart.
 

·
#8 Post ho
1999 Subaru Forester
Joined
·
2,439 Posts
If the smaller filter is problematic, Subaru wouldn't have designed the engine to use that size.
 

·
Administrator
2016 & 2018 2.5i Premium CVT
Joined
·
19,354 Posts
erhayes said:
Subaru engineers know what is needed for their engines ... Why we keep trying to be mechanical and lubracation engineers and out guess the factory data and recomendations is not too smart.
Your view of the Subaru engineers might be true--probably is--but the final decision on what goes into a car is a mix of engineering, style, marketing, and economics. Considering the multipliers involved, economics is a big part of that decision. Surely the engineers didn't have the final word in things such as how to replace the foglight bulbs, for example. Or whether the DRLs should be controlled by a cheap and wasteful resistor or a more expensive, active circuit that was more energy efficient.

The aftermarket provides us the opportunity to optimize the mix against our own criteria.
 

·
Registered
2006 Forester
Joined
·
174 Posts
Subaru doesn't "design" a filter- trust me on this. They focus on the motor, the transmission, and the basic interior. They get bids on stuff like filters and as long as the bidder meets certain automotive specs and is a reliable AND a low bidder, they get the bid. There are two manufacturers in Japan that make filters for Honda and two other manufacturers. They are more expensive so people keep dumping them and trying others and then coming back (Toyo Reki may be the name of them). Anyway, an OEM filter is not necessarily the best option since others have better media and higher tolerances. Just because it has a Subaru stamp on it doesn't mean it is the best for that vehicle and the source can change from year to year.

After all the research I have seen, I like Wix, Baldwin, and Mobil1 (a good version of Champion) but I think the Balwin is the best. Balwin has been making filters and media for a long time and is the dominant player in the heavy duty industry (trucks/farm equipment). I like their focus on filter media itself and their attention to the weak-link parts of the filter. Their filters are now my choice after using Mobil 1 and Wix for a long time. Their media filters dirt extremely well and are overbuilt in many ways. There is no way I am using Subaru filters- they could be made by Purolator today and Fram tomorrow. I like the Japanese version of the Honda filters too but they have two so you have to pick the right one. The Canadian version is a third option and isn't built as well. Remember- Subaru doesn't make them or have any expertise in the filter business so they can't even guide their suppliers besides insisting on certain industry specs. No think if another supplier came along and dropped the price by $1 per filter. If Subaru sells 500,000 cars, that is half a million dollars saved right off the bat. As long as they meet the minimum specs, chances are they will use the cheaper guys. Me? I'm using Baldwin, Wix, or Mobil1.
 

·
Registered
1998 Forester "S" lifted. Bog-o-matic
Joined
·
2,006 Posts
Tokyo Roki makes the Fuji filters (black,small)


Purolator makes the old filters (were big, then small, all leaked and were junk)
 

·
Administrator
2016 & 2018 2.5i Premium CVT
Joined
·
19,354 Posts
Never heard of Baldwin. Where does one get them?

I've done 79k miles OK with Fram Tough Guard, but am always open to better data.
 

·
Administrator
2016 & 2018 2.5i Premium CVT
Joined
·
19,354 Posts
SenorSubie said:
Here's a good link to some comparisons of various filters (found on another thread here)
Been there before. But it doesn't mention Baldwin.
 

·
Registered
2006 Forester
Joined
·
174 Posts
bbottomley said:
Never heard of Baldwin. Where does one get them?

I've done 79k miles OK with Fram Tough Guard, but am always open to better data.
http://www.baldwinfilter.com/

http://www.baldwinfilters.com.au/ ---They are also in Australia

Here is their website. The Forester filter # is B1400 and you can do a search for local distributors by zip code. Don't worry if they all seem to be semi or farm equipment or heavy duty stores. All you have to do is ask for B1400 or they can also order them.

Read up on them and maybe do a yahoo/google search for Baldwin filter test or review. I've read very positive reviews on them- not a single bad one. They didn't become so dominant in the industrial sector by making cheap or ineffective filters. At least, that's how I look at it and after looking at everything else I could find.
 

·
The Modfather
2019 Impreza 5dr Sport - Manual
Joined
·
8,070 Posts
Just some info on WIX filters

51334 = large filter (H6) will fit H4 non turbo but not on the Turbo motor

51365 = small filter (H4)

While Subaru has now specified the smaller filter for both the NA and turbo H4 motors (
15208AA100 - most likely to reduce confusion and space taken up in store room) For the NA motor the larger filter will fit AFAIK as you have the room under there. The reason the turbo motor is not supposed to us the larger one is the filter is too close to the header and during idle can cook the oil. Here are the specs for the two Subaru WIX filters:
 

Attachments

1 - 20 of 21 Posts
Top