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2019 White 2.5 Premium
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17 Posts
Discussion Starter · #1 ·
2019 Outback, 2.5l.

Has anybody else noticed that it takes a looong time for the oil to drain from the oil filter mounting cup when doing an oil change? Almost to the point where I wonder if there is some sort of obstruction.

I'm using an OEM filter, and have a Fumoto valve.

My procedure is:

1. open Fumoto valve and let the oil drain until it slows to a small trickle (maybe 5 mins or so)
2. crack the oil fill cap and unseat the dipstick, just to ensure there isn't any pressure built up somewhere
3. remove the filter, let the oil drain from the filter cup.
4. close the Fumoto valve
5. replace the filter
6. refill the oil and button everything up

Using the above procedure, maybe a cup of oil drains out of the filter and ends up in the metal filter cup (both inside and outside the circular filter mount) at step 3. I would expect it to drain pretty quickly back into the crankcase via the hole inside the circular filter mount, but it doesn't. Even after 10 mins or so there is still oil there. It almost seems like there's some sort of obstruction or air bubble impeding the draining process. I wonder if it has something to do with the Fumoto? Seems unlikely but I can't come up with anything else.

I did the first oil change without the Fumoto valve and don't recall this occurring, but my memory is a little hazy on that. This has happened the last couple of oil changes with the Fumoto though.
 

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2001 Outback Wagon 3.0 VDC
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358 Posts
Can I make a suggestion for your routine?

1. Loosen the filter just to the point where it becomes loose enough to turn easily by hand (so about 1 full turn)

2. Remove filler cap and pull distinct

3. Drain oil until it starts to drip

4. Close drain plug

5. Remove and replace oil filter

6. Fill engine with oil

7. I'm sure you know the rest.

The reason I say to loosen the filter first is that I have 90% success doing it this way so the filter cup does not fill with oil, I loosen the filter JUST enough where the oil seal is barely touching the sealing surface, try it next time and see what happens.
 

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2017 Outback 2.5i Limited
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223 Posts
Grum seems to have a good procedure. However, if you a worried about a sort of vapor/oil lock in the filter knock a small hole in the top of the filter with an ice pick, nail, etc. which would allow air to flow in the closed filter to break the suction. Simple hillbilly solution so take it for what it's worth.
 

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SubaruOutback.org Founder
2021 Outback Limited 2.5L - 🍦The Ice Cream Man🍦
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5,658 Posts
I am curious to know why it should matter whether or not the remnant of oil from the oil filter drains back into the engine? Why oil would drain from the filter has to do primarily with the filter's anti-drainback valve which oftentimes does not fully seal prior to removal and I have had leakage from filters using both a nitrile and silicone ADBV. I wipe out that cup at every oil filter change, frankly I don't want that oil going back into the engine if I can help it. There is certainly no way to gauge how long it would take for said oil, drained back into the engine, to make its way down to be drained from the crankcase. For all we know it doesn't make it back to the crankcase but rather gets stuck in another point in the oiling system from which it cannot be immediately drained.
 

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2020 Subaru Outback XT Limited
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83 Posts
You will notice if the oil is cold the oil will stay in the cup. If the oil is hot it will drain properly.
 

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Premium Member
2020 Onyx
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13,508 Posts
I never have oil flood out of my oil filter into the cup when changing oil and it made me think about the anti-drainback valve function and why my oil filter isn't 100% filled with oil when I remove it.

Please correct me if something's wrong with this thinking about the anti-drainback valve in a vertically mounted oil filter like ours:

In normal operation the oil system lets oil flow into the filter from the outer ring of holes in the base plate and then returns to the engine through the center threaded section.

The anti-drainback valve prevents reverse-flow when the engine is shut off, so that oil doesn't leak out from the ring of holes back into the engine. If by chance you had metal particles in the oil filter, unless they were stuck to the filtering media, could fall back into the engine if it weren't for the anti-drainback valve.

But nothing prevents the oil from draining from the center core, and oil can seep through the filtering media to drain back into the central hole when the engine is shut off. Assuming the oil was hot when the engine was shut off, it's thin and not viscous and can seep through the media, nearly emptying the oil filter.

If you have an ice-cold engine and start the engine just long enough to put it on a ramp or move half way out of the driveway or something, the oil is still cold and now your oil filter is full of cold viscous oil, which might take hours to seep through the media and out of the center core if at all, but the center core itself should be empty. Oil would only be in the outer part of the oil filter, above the anti-drainback valve.

Suppose the anti-drainback valve were missing or ineffective. The oil would be draining back into the engine through the peripheral holes and your oil filter should be nearly empty.

Suppose the anti-drainback valve is working and you remove the oil filter - the oil should stay in the filter except what would drain out of the center core.

Under what situation would the oil filter be full of oil when it's removed, such that oil floods out of it? I can't understand it.
 

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2012 OB , 2017 Impreza
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3,798 Posts
Oil must be as hot as you can get it before draining. I usually plan an oil-drain at the end of the day after using the vehicle.

I do not get oil in the "filter cup"....hence there is never a need to wait for it to drain.

When I loosen the oil-filter just enough, then I wait until the filter completely drains INTO THE THE ENGINE (then out the fumoto valve.)

In this way, when I remove the filter, there is nary a drop to spill out into the catch-cup which surrounds its base.
 

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18 Outback 3.6r Touring
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741 Posts
I've done many top filter oil changes and would suggest the follow order from what you have. I kept your numbering so you can see the difference.
2. crack the oil fill cap and unseat the dipstick, just to ensure there isn't any pressure built up somewhere
3. remove the filter, let the oil drain from the filter cup.
1. open Fumoto valve and let the oil drain until it slows to a small trickle (maybe 5 mins or so)
5. replace the filter
4. close the Fumoto valve
6. refill the oil and button everything up
 
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