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Old 03-27-2013, 07:30 PM   #1
This Is Not Mike
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Member#: 131737
Join Date: Nov 2006
Chapter/Region: NESIC
Location: Mass
2006 STI OBP
2013 Tacoma TRD OR

Default Cooling System Questions - Overflowing Radiator, Low Overflow Bottle

Hi all,

Hoping someone could restore my sanity on this one.

The STi has been sitting most of winter, with the occasional once a week or so drive around the block to get the fluids up to temp. Last weekend I had swapped to my summer wheels (yeah yeah) and I noticed a whiff of coolant from the engine bay, so I popped the hood and noticed my coolant overflow was on the low level. I had probably only been driving the car for 20 minutes, it was up to temperature coolant wise, but it wasn't on for my longer than that. I should note that I've never had any issues with overheating, my coolant temperature has always been spot-on.

Today I had to jump my car to get it started so I had let it run for maybe 3 minutes and I wanted to check to see if any bubbles were coming out of the radiator itself. When I removed the cap coolant was overflowing out of the neck.

I then killed the car and released the pressure from the system slowly (as there wasn't much). The car was probably on the first notch from the "C" mark. With the car off the level in the radiator was right to the neck. When I turned the car on with the cap off, I didn't see any bubbles, but after about 30 seconds the level rose to overflow the radiator cap.

I'm still low on the coolant overflow, so I'm wondering what is going on here, and why it was overflowing out of the radiator and not flowing over to the overflow level.

I did have the coolant changed about 1,800 miles ago at the local dealer. In between, I was tuned and did do a few WOT runs. The cooling system is all original (radiator, hoses, t-stat, etc). I also had a UOA done about 1,800 miles ago and the oil came back coolant free, so I'm reluctant to jump to HG issues.

I'm ultimately probably going to bring it to the dealer to have them look at it, but I didn't know if there was anything blatantly obvious I'm missing to check. At first I had assumed I was just low on coolant, but the fact the coolant spilled out of the radiator over going to the overflow has me wondering if something is up.

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Old 03-28-2013, 01:46 AM   #2
Scooby Specialist
Member#: 269388
Join Date: Jan 2011
Chapter/Region: SCIC
Location: SoCal SD / LA
2011 Impreza WRX



im pretty sure that's normal

car on for awhile, coolant will go to min in the reservoir. After you let it sit for awhile, it'll go back to max in the reservoir. The coolant is being cycled... that's all
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Old 03-28-2013, 02:06 AM   #3
Scooby Specialist
Member#: 28716
Join Date: Nov 2002
Chapter/Region: SCIC
Location: Los Angeles
2006 STI


Catching a whiff of coolant probably means your radiator's starting to leak. Sometimes you can see the coolant running along the seams where the aluminum is crimped to the plastic but having a pressure test done is the best way to find out.
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Old 03-28-2013, 11:54 AM   #4
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Join Date: Jan 2007
Chapter/Region: BAIC
Location: North Bay
2005 STI


The coolant expansion (overflow tank) and radiator will constantly go up and down based on the system and how coolant is expanding. Usually it will stay between low and high mark in the expansion tank.

If by chance you are leaking between the actual radiator and expansion tank, maybe there is a small hole in the hose that goes to the expansion and leaking out, you would smell coolant. However coolant is one of them things that seem to linger around once spilled. So it could be that someone spilled a bit when servicing your car and you are smelling it still. But clearly you'd want to look for puddles or small areas that might be saturated with coolant in your engine bay.

If you are concerned you do not have enough coolant in the system due to a leak or some how loss of coolant. The best bet is to fill the system back up and purge the system of any air. The best and only true way of doing this is at the filler neck near the turbo and with a spill proof funnel. It will allow you to properly purge any air out as well as ensure you have all the correct coolant level.

What you described as far as the coolant spilling from Radiator opening (with cap removed) is normal. The system is pressurized and when it is time to breach and expand to the coolant overflow, the radiator caps valve will open and allow the expansion to occur. However if we just run the with no cap on, it will spill over. Again the best way to test this is with a spill proof funnel, you can use it at the radiator as well but it is recommended to use the filler tank near the turbo and make sure your levels are where they should be. Or have someone check the coolant levels.

Good luck.
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