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Old 06-30-2005, 10:49 AM   #1
Undepelo
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Question STi oil filter seems too small. What about a bigger filter and a heat shield?

I've seen the Impreza oil filter go from huge to microscopic in a few years, which sucks. I just realized that the filter for my 05 STi is the same as my wife's 02 Mazda Protégé 5! I have read that the push for a smaller filter on Imprezas was to keep them from being too close to the header (heat transfer to the oil) . So what about going back to the older, bigger filter and making a oil filter heat sheild? Anyone remember what the old Purolator Pure One part number was for the Impreza? Any thoughts?
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Old 06-30-2005, 10:50 AM   #2
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No need for a larger filter. In fact why would you want a larger filter? The STi filter is the very same as the WRX filter.
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Old 06-30-2005, 10:55 AM   #3
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Quote:
Originally Posted by conker69
No need for a larger filter. In fact why would you want a larger filter? The STi filter is the very same as the WRX filter.
More filtration media provides more filtration efficiency for a longer time. You have a lower restrictive filter for a longer time. Also means you have more protection on long interval oil changes with synthetic oils.
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Old 06-30-2005, 11:02 AM   #4
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Purolator does make a Pure One filter that is the same as their filter for the STi except that it is slightly longer. Dia., sealing surface, thread pitch is all the same as their filter for the STi. I do not remember the exact part number though. However, it is the exact filter specified for my wife's 03 Honda Element. Check out the fitment guide for the Element and you will have the longer filter for the STi. The last time I changed the oil on both cars, I was going to just get two of the longer filter, but they only had one of each in stock. Next time, I'll make sure to get the longer one. HTH

Fred
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Old 06-30-2005, 11:05 AM   #5
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Quote:
Originally Posted by Chayse
Purolator does make a Pure One filter that is the same as their filter for the STi except that it is slightly longer. Dia., sealing surface, thread pitch is all the same as their filter for the STi. I do not remember the exact part number though. However, it is the exact filter specified for my wife's 03 Honda Element. Check out the fitment guide for the Element and you will have the longer filter for the STi. The last time I changed the oil on both cars, I was going to just get two of the longer filter, but they only had one of each in stock. Next time, I'll make sure to get the longer one. HTH

Fred
Ahh you see, now we are getting somewhere..
Just about how much longer would you say that filter is?
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Old 06-30-2005, 11:11 AM   #6
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I'm pretty sure there are better things to worry about. That filter is spec'd with (without a doubt) a significant factor of safety. Its probably at least double what is required for the engine. You're engine is only .5 liters bigger than your wives, the block is the same size as a 2.0 wrx Why would you think you need a bigger filter???
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Old 06-30-2005, 11:14 AM   #7
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Quote:
Originally Posted by Undepelo
More filtration media provides more filtration efficiency for a longer time. You have a lower restrictive filter for a longer time. Also means you have more protection on long interval oil changes with synthetic oils.
I thought this is what you were going to say. A bigger filter means you can filter a larger quantity of oil per unit of time which means you need more oil in the engine. I don't see how this has anything to do with the life of the filter. The OEM filter works just fine and my wife's Xterra (V-6) has a smaller filter (Mobil 1) than my STi. I change the oil according to the service manual (5000 mile intervals) and we have not had a single issue for over 30000 miles.
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Old 06-30-2005, 11:26 AM   #8
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Quote:
Originally Posted by REX8
I'm pretty sure there are better things to worry about. That filter is spec'd with (without a doubt) a significant factor of safety. Its probably at least double what is required for the engine. You're engine is only .5 liters bigger than your wives, the block is the same size as a 2.0 wrx Why would you think you need a bigger filter???
Your statement with regard to the margin of safety employed in the design of the current filter is based on fact or is it just your assumption? If this were true, then wouldn’t that mean the first filter was designed to last 5-6 times longer than needed? Why would they have done this in the first place? How do you know that the only design considerations for the oil filter is performance versus price, availability, commonality etc...? My engine is .5L larger but it’s not turbo, which is a different environment.
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Old 06-30-2005, 11:38 AM   #9
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Quote:
Originally Posted by conker69
I thought this is what you were going to say. A bigger filter means you can filter a larger quantity of oil per unit of time which means you need more oil in the engine. I don't see how this has anything to do with the life of the filter. The OEM filter works just fine and my wife's Xterra (V-6) has a smaller filter (Mobil 1) than my STi. I change the oil according to the service manual (5000 mile intervals) and we have not had a single issue for over 30000 miles.
The flow rate (quantity of oil per unit of time) is not dependant on the filter unless the filter restricts flow significantly, in which case the flow is reduced and the pressure before the filter is increased. If this has nothing to do with filter life then how come filters are different sizes? Wouldn’t it make sense then to make all the filters very tiny and all the same? The more filtering media, the more oil flows through the filter with a lower pressure drop across the filter. This in turn keeps the pressure at the engine parts high, which is good.
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Old 06-30-2005, 01:14 PM   #10
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You do realize that you are trying to out engineer a team of professional engineers at Subaru who specialize in this sort of stuff right? While you are free to do so, realize that your efforts are really for naught. If you are THAT concerned, get off the wallet and buy a $200 bypass unit that filters your oil to HEPA levels. This will both relocate and outfilter the OEM unit.
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Old 06-30-2005, 01:47 PM   #11
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Quote:
Originally Posted by Unabomber
You do realize that you are trying to out engineer a team of professional engineers at Subaru who specialize in this sort of stuff right? While you are free to do so, realize that your efforts are really for naught. If you are THAT concerned, get off the wallet and buy a $200 bypass unit that filters your oil to HEPA levels. This will both relocate and outfilter the OEM unit.
Those professional engineers are bound by design criteria that limit their designing capability. They must make many compromises and, for example, find a design that will produce the best product at the lowest cost. Unfortunately cost it usually high at the priority list often first. I would never question a surgeon’s technique on how to perform heart surgery but I feel comfortable being critical of mechanical systems I can improve by deciding what design criteria I can live with. I don’t care if Subaru saves $0.02 by going with a smaller filter, I would prefer the peace of mind of spending a $2.00 more for a filter that will perform better when used for +7500 miles.
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Old 06-30-2005, 02:08 PM   #12
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Quote:
Originally Posted by Undepelo
Those professional engineers are bound by design criteria that limit their designing capability. They must make many compromises and, for example, find a design that will produce the best product at the lowest cost. Unfortunately cost it usually high at the priority list often first. I would never question a surgeon’s technique on how to perform heart surgery but I feel comfortable being critical of mechanical systems I can improve by deciding what design criteria I can live with. I don’t care if Subaru saves $0.02 by going with a smaller filter, I would prefer the peace of mind of spending a $2.00 more for a filter that will perform better when used for +7500 miles.
Ditto. You'd be surprised at the cost cutting that goes on in making a car profitable; even just to save pennies. (more-so with high volume cars)
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Old 06-30-2005, 03:32 PM   #13
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Somebody over on IWSTi.com purchased and cut open a large number of the most poplular filters and compared the internals. The consensus was the stock filter was one of the best ones out there in terms of construction and/or filter media area.
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Old 06-30-2005, 03:39 PM   #14
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Quote:
Originally Posted by majmun
Somebody over on IWSTi.com purchased and cut open a large number of the most poplular filters and compared the internals. The consensus was the stock filter was one of the best ones out there in terms of construction and/or filter media area.
But all being equal, a bigger filter will have a larger filtration area which means it will filter more, longer and with fewer losses. I would prefer the old OEM filter that was a bit larger, but I don't think they are made anymore.
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Old 06-30-2005, 05:21 PM   #15
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Quote:
Originally Posted by Undepelo
Those professional engineers are bound by design criteria that limit their designing capability. They must make many compromises and, for example, find a design that will produce the best product at the lowest cost. Unfortunately cost it usually high at the priority list often first. I would never question a surgeon’s technique on how to perform heart surgery but I feel comfortable being critical of mechanical systems I can improve by deciding what design criteria I can live with. I don’t care if Subaru saves $0.02 by going with a smaller filter, I would prefer the peace of mind of spending a $2.00 more for a filter that will perform better when used for +7500 miles.
have you bought the new -80 or -100 filters? i have and they are made by tokyo roki who is one of the best oil filter companies in japan. they make the japanese filters for honda that many honda people try to import and pay $$ for.

the subura filter is a quality filter, my dealer charges $6.50 and it's well worth it. i change w/ M1 oil every 4k, imo if your so concernced about clean oil then why would even consider changing it at 7.5K intervals.
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Old 07-04-2005, 10:44 AM   #16
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Quote:
Originally Posted by Undepelo
But all being equal, a bigger filter will have a larger filtration area which means it will filter more, longer and with fewer losses. I would prefer the old OEM filter that was a bit larger, but I don't think they are made anymore.
Actually the smaller filter has more filtering capability. Mostly because all things aren't equal. It's the type of filter media not the size of the filter itself that determines how well it filters.

PN 15208AC060 filter surface area 760cm2

PN 15208AA100 filter surface area 800cm2 (a 5% difference)
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Old 07-04-2005, 05:51 PM   #17
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Quote:
Originally Posted by Undepelo
But all being equal, a bigger filter will have a larger filtration area which means it will filter more, longer and with fewer losses. I would prefer the old OEM filter that was a bit larger, but I don't think they are made anymore.
The OT answer:

So, big women have loose p*****s, all things being equal, of course?


Dude, I understand your desire to baby your investment to the 'nth degree. THere is a place I know of, full of like-minded people, that could become home to you:

www.bobistheoilguy.com

There, you can discuss the minutae of polyol esters, lube control, flow vs. filtration, and dancing green elves turned golden.

Last edited by poison; 07-04-2005 at 05:57 PM.
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