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Premium Member
2006 Impreza WRX with PPP Manual of course! ;-)
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1,522 Posts
Discussion Starter #1
I was doing my oil change the other week, and peeked at the radiator cooling fluid level. It was half way between the min and max marks on the coolant reservoir. The engine was only warmed up enough to do the oil change, and so looking at it today with the engine cold it was down towards the bottom of the tank.

I was wondering what the correct procedure was for filling and checking this level (a quick search didn't turn up anything...).

I'm running an European 01 model SF5 S-turbo by the way.
 

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The Modfather
2019 Impreza 5dr Sport - Manual
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8,052 Posts
What I do is this. With a stone cold motor I take off the radiator cap and make sure coolant is up to the top. If not I put coolant in of course (I have a gallon of subaru coolant from the dealer) I mix a 50:50 blend of coolant and distilled water. If the coolant is up to the top, I then take a flashlight and look at the overflow. I like to have it down to the minimum line at the very least. If it's not then I do the mix deal and fill it to just above the minimum mark. Later when I come home with a warm motor I make sure the level is above the minimum somewhere to the max line. Recently I checked my wife's Tribeca and the level was low in the radiator by about a cup. I filled it up and noticed there was fluid in the overflow. That means the radiator cap was not doing it's job. So I called Ben and ordered one for her Tribeca and one for my Forester. To me it's cheap insurance to change out the radiator cap every few years. Radiators (and motors) are expensive compared to the cap ;)
 

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Premium Member
2006 Impreza WRX with PPP Manual of course! ;-)
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1,522 Posts
Discussion Starter #3
Cheers Peaty, it was the relationship between the overflow and the radiator that was puzzling me... all clear now, thanks!
 

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Premium Member
2006 Impreza WRX with PPP Manual of course! ;-)
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1,522 Posts
Discussion Starter #4
I just took a look at the manual... there's a really good section on checking the coolant fluid levels... d'ohhhhhhhhhh... :chair:
 

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Registered
2005 STi
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12 Posts
I've always filled to the max level when cold, since the 'max' is so low on the reservoir it gives plenty of room for expansion, and this gives you alittle extra buffer if you should develop a slow leak.

Changing the cap every couple of years is definitly a good idea too!
 

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Administrator
2007 Forester Sports XT 4EAT
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38,716 Posts
I've always filled to the max level when cold, since the 'max' is so low on the reservoir it gives plenty of room for expansion, and this gives you alittle extra buffer if you should develop a slow leak.

Changing the cap every couple of years is definitly a good idea too!
I fill all my vehicles the same way. I check the coolant level when it's "cold" & I fill it to the "full" mark. The level rises when hot, but never close to overflowing. :wink:

As to the cap. I had a faultly one on my '03X. It casused the upper hose to collapse when it was cooling down. Very strange! :icon_eek:

Bobby...

My MODding Journal
 

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The Modfather
2019 Impreza 5dr Sport - Manual
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8,052 Posts
As to the cap. I had a faulty one on my '03X. It caused the upper hose to collapse when it was cooling down. Very strange!
If you look under the cap there is a little silver button at the center of the gasket material. The button is a check valve that will drop down a little and let coolant in but not out. When you start the car and the coolant gets hot, it expands and pushes past the gasket material. The hot coolant goes into the overflow tank. The tube in the tank goes all the way to the bottom. When you turn the car off, the coolant contracts as it cools down, that little button check valve opens up and the coolant from the overflow gets drawn back into the radiator. If the spring goes bad on the little button and won't let the new coolant in it creates a vacuum in the system and you hoses can collapse.
 

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Registered
2005 XS
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166 Posts
Peaty,

The mechanic at the dealer told me there was a tech bulletin on the radiator cap and the siphon tube. They were to check the gasket on the cap and maybe clean away any crud if any had formed (maybe something else, but it wasn't needed to replace the cap) and to trim the siphon line so it didn't touch the bottom of the overflow tank. I think they were to trim the tube with a 45 degree cut on end and have the trimmed tube hang about 1/4" above the bottom of the tank. They did that to my car, a 2005 XS.

Ray Lovinggood
Carrboro, North Carolina, USA
 
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