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Old 11-24-2008, 11:33 PM   #1
Scooby Newbie
Member#: 61212
Join Date: May 2004
Chapter/Region: BAIC
Location: Bay Area, CA
2005 STi

Default Overheading/Coolant Overflow

so at a recent trackday, i ran my accessport as a water temp gauge the entire time, and never got above 205 degrees on the track. (about an 80-85 degree dry day).

When i was at the track i noticed that coolant pushed out into my overflow bottle and it was nearly full (way past the full line, the container itself was almost to the top). I thought it would suck back into the system as soon as the car cooled down.

I drove home from the track almost all the way without issue (about a 120 mile drive). Temps stayed in the 180 degree range (accessport in the entire time), when i was a block from home the dummy gauge started rising, and i hit about 215-220. Thank goodness i was already close to home, just shut the car off and pushed it home, (temp never excceeded 220, was not able to reach 3/4 temp gauge on the dummy gauge yet - saved my headgasket lol).

I ended up waiting for the car to cool down, and i detached the overflow bottle and filled the system back up, and burped the system again. I got most of the coolant from the overflow tank back into the top resivor. when i was finished burping the system, my overflow tank was back to the normal "full" line.

My question is: why didn't the coolant pull back into the system after pushing out? Is it supposed to pull back in, or am i supposed to pour it back in everytime i run hot temps?

My cooling mods are:

Koyo Radiator
Gimmick 170 degree t-stat
Gimmick Radiator hoses
STi 1.3 bar radiator cap for top resivor, stock 137kpa cap on the radiator

Ever since i poured the coolant back into the system, everythign has been fine, normal temps range from 170-200, never above 205.
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ChuiSTi is offline   Reply With Quote
Old 11-25-2008, 05:34 AM   #2
Scooby Specialist
Member#: 172501
Join Date: Feb 2008

ideally its supposed to pull it back in- But its never supposed to overflow that much-. there are only a few conditions that can cause that, and that involves either some coolant becoming steam, or some exhaust gases being blown past the head gasket.

When the car overheats, some of the coolant will turn to steam. Steam takes up a lot more room, and pushes the coolant to displace. As the coolant displaces, it gets hotter, so more steam is formed, displacing even more coolant.

Ideally, most of the coolant should be sucked back in- as the steam cools, it will turn back into liquid, and suck the coolant from the overflow. Steam production is no good.

I'd start with replacing the radiator cap. I'd also check for restrictions int he overflow tube.

Also make sure you have the subaru coolant additive in there.
madmax718 is offline   Reply With Quote
Old 11-25-2008, 06:28 PM   #3
Scooby Newbie
Member#: 61212
Join Date: May 2004
Chapter/Region: BAIC
Location: Bay Area, CA
2005 STi


oh yea so i found a kink on the upper line going to the remote resivor, but the lower line is fine, do both need to have slack to be able for coolant to pull back in?

I have the cooling system conditioner, subaru coolant (green), distilled water, and a bottle of water wetter in there. coolant/water is 50/50
ChuiSTi is offline   Reply With Quote

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