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09 Outback SE
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23 Posts
Discussion Starter · #1 ·
I understand that with modern oils, particularly synthetics, that extended drain intervals are possible because the oil simply doesn't break down as quickly (if at all) as older oils did.

What I don't understand is how the filters last for a long time without filling to capacity with fine grit and other contaminants - particularly since the filter on my '09 Outback is so small.

If I run extended drain intervals isn't it likely that my oil is technically fine but I am still damaging my engine because the filter is allowing contaminants to flow through when it reaches capacity? Wouldn't I have to change the filter more frequently than the oil?

Thank you.
 

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2013 OB 2.5i Premium/DDD Graphite Gray Metallic OP#2 Weathertec Window Deflectors
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405 Posts
I understand that with modern oils, particularly synthetics, that extended drain intervals are possible because the oil simply doesn't break down as quickly (if at all) as older oils did.

What I don't understand is how the filters last for a long time without filling to capacity with fine grit and other contaminants - particularly since the filter on my '09 Outback is so small.

If I run extended drain intervals isn't it likely that my oil is technically fine but I am still damaging my engine because the filter is allowing contaminants to flow through when it reaches capacity? Wouldn't I have to change the filter more frequently than the oil?

Thank you.
There is less contaminant's with full synthetics, that's why it cost twice as much.So they say,slipper the better.
 

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(formerly) 03 H6 OBW , (presently) 06 WRX Sportwagon & 2021 Honda CR-V
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18,332 Posts
probably reading over at bobistheoilguy.com would answer best.

But the 2 things that come to mind are, many folks who do run extended (say, 12-15K miles or more) change the filter and top-off halfway through.

But, as mentioned, IF one reason filter need changing is from varnish buildup, synthetics are superior at keeping varnish dissolved/suspended and that 'may' be a reason filters could last longer.
 

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Fresh Out of Outbacks!
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14,475 Posts
A UOA would let you know what type of contaminants you happen to get in your situation.

If you're committed to it, changing a filter midway through the change interval is perfectly acceptable. Just do the math to make sure you are still saving money vs. normal oil at normal interval.
 

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2011 Outback Limited/2.5L/CVT
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390 Posts
The best, full synthetic (micro glass) media oil filters have several times the dirt holding capacity of a cellulose media filter. In addition synthetics simply run cleaner and generate less insoluble materials to be filtered out. I've run oil change intervals up to 18,000 miles in my Subaru's using Amsoil and their standard sized, EAO-12 oil filter and the oil shows no excessive thickening from getting loaded up with contaminants.

In the vast majority of cases, the filter will last longer than whatever oil you're using. Other excellent high capacity oil filters are made by Mobil, Bosch, K&N, Royal Purple, etc...

TS
 

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2012 limited, white, no moonroof or nav
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1,696 Posts
Most of the particulates that the filter is meant to catch are carbon bits, which a product of both fuel and oil being burned. Synthetic oil does a better job of both holding these products in suspension (in a liquid state) and not burning in the first place.

I do not do extended drain intervals, because I am old and set in my ways. But I have cut open filters while using synthetic oil.......There is very little to be found in the media, after 5k miles. If you extrapolate, the filters would probably not get loaded in 20k. YMMV.
 
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