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2001 OBW VDC, 2004 WRX, 1999 LEGACY L (in a heap)
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Discussion Starter #1
I was installing my Fumoto on the last oil change on the VDC, and while I was up under there (after having just put it on ramps)I saw that the lower hose was collapsed... upper hose unaffected, never observed it collapsing.

not sure how to interpret that....suggestions?
 

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2008 Outback 2.5
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966 Posts
Collapsing is a sign of the fluid contracting and trying to suck back in from the reservoir. A collapsed hose will impede this.

I just replaced my upper and lower hoses on my 08 Base with 150k miles this weekend. The hoses were pretty soft and the coolant had some pieces of black rubber in it even though it had been less than 2 years since changing. I would recommend changing the hoses if they are anywhere near as old. They're only $10 and $15 each for Dayco hoses which are "sort of" formed to the right shape. Beware that the spring clips will need to be really opened wide with new hoses because they tend to compress the old hoses quite a bit.
 

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2001 OBW VDC, 2004 WRX, 1999 LEGACY L (in a heap)
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1,302 Posts
Discussion Starter #3
i see that described as a symptom of upper hose collapse when I run searches, but I don't find anything talking about lower hose collapse...
 

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On the Super Mod Squad
2002 3.0 VDC Wag + 2018 2.5 Leg Ltd
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26,480 Posts
subaru ones $20 each.

upper 45161AE05A

45161AE07A

edit: these are the same on 2001-2004 H6.
 

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2001 OBW VDC, 2004 WRX, 1999 LEGACY L (in a heap)
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1,302 Posts
Discussion Starter #5
yeah, not a big deal to dump coolant and swap them. The lower one appears stock(yikes 200k), but the upper one is some advance or oriellys hose.

I was just wondering if there was another reason there would be a vaccum only down there.
 

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2008 Subaru Outback PZEV,2010 Impreza 2.5i
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538 Posts
Another cause could be blocked hose drawing fluid (and discharging ) from radiator cap. I had top radiator hose collapsing due to clogged hose from radiator to overflow reservoir.
 

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2001 OBW VDC, 2004 WRX, 1999 LEGACY L (in a heap)
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Discussion Starter #8
But the top hose is a-okay... its only the bottom thats collapsing. Thats why I'm confoozed.

There is a problem also, I have some strange non-standard radiator in the darn thing, an OEM cap doesnt fit it, i found out a couple years ago...
 

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I was installing my Fumoto on the last oil change on the VDC, and while I was up under there (after having just put it on ramps)I saw that the lower hose was collapsed... upper hose unaffected, never observed it collapsing.

not sure how to interpret that....suggestions?
The hose with the weakest walls will collapse when the return path from the external reservoir to the radiator isn't working as the engine cools.

Regardless of which hose collapses, removing the rad cap should result in the hose returning to it's normal shape.

If the hose doesn't respond, then the hose has lost it's wall strength and shape. It should be replaced.

The ability of the rubber cooling system hoses to stretch a limited (by design) amount is actually what provides the pressure in the engine cooling system. A weak hose will not only tend to collapse as the engine cools, but could also balloon outward as the engine heats up, and not provide adequate pressure to control the boiling point. This can lead to odd coolant loss or overheating symptoms.
 

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2008 Subaru Outback PZEV,2010 Impreza 2.5i
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The hose with the weakest walls will collapse when the return path from the external reservoir to the radiator isn't working as the engine cools.

Regardless of which hose collapses, removing the rad cap should result in the hose returning to it's normal shape.

If the hose doesn't respond, then the hose has lost it's wall strength and shape. It should be replaced.
Totally agree. It does not matter which hose collapses. The system is designed to pump hot expanded fluid to the reservoir by keeping walls of all the hoses relatively the same. When the engine cools down if the wall strength is the same, then the system should draw cold fluid back from the reservoir to the radiator. Your lower hose lost its wall strength and unable to perform as Plain OM explained. Please replace the collapsed hose.
 

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2001 VDC/SC One of a Kind
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14,775 Posts
The hose with the weakest walls will collapse when the return path from the external reservoir to the radiator isn't working as the engine cools.

Regardless of which hose collapses, removing the rad cap should result in the hose returning to it's normal shape.

If the hose doesn't respond, then the hose has lost it's wall strength and shape. It should be replaced.

The ability of the rubber cooling system hoses to stretch a limited (by design) amount is actually what provides the pressure in the engine cooling system. A weak hose will not only tend to collapse as the engine cools, but could also balloon outward as the engine heats up, and not provide adequate pressure to control the boiling point. This can lead to odd coolant loss or overheating symptoms.
Radiator cap.

It's not opening on engine cooldown so the vacuum is collapsing the hose instead of drawing coolant from the recovery reservoir.
All good info. :29:
 

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Just so that there isn't any misunderstanding, the fact that a hose is found collapsed when the engine cools doesn't necessarily mean the hose is bad.

If the return of coolant from the external reservoir to the radiator is indeed blocked, then as the engine cools something has to give to accommodate the reduced volume of coolant in the engine system; this will most likely (and preferably!) be one or more of the rubber hoses.

The issue of whether or not a hose needs be replaced is addressed by what happens when the rad cap is removed and also when the cooling system is under pressure. If the collapsed hose springs back out to its normal shape when the cap is removed, and it doesn't stretch out abnormally when the system is under pressure, then it might still be fine.

In any event, the root cause of the collapse is elsewhere, and that should be dealt with. Incorrect/ill-fitting/faulty rad cap, blocked reservoir hose, and accumulated gunk in the bottom of the reservoir are common.
 

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2008 Outback 2.5i, 2009 Forrester 2.5 sohc
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I had the issue with the upper hose, replaced with a NAPA and the hose didnt fit exactly right, and i keep smelling coolant. Replaced with dealer hose a couple months ago, and smell is gone.

IMHO, use only dealer OEM hoses with OEM spring clamps, you get 100K+ miles from them.
 
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