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Old 08-27-2012, 04:17 PM   #1
BigJ02wrx
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2002 WRX
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Default Please help diagnose my overheating problem

I recently replaced my cracked OEM radiator with a Koyo. I also replaced the thermostat with an OEM replacement and the radiator cap with a Koyo. The temp gauge randomly rises and falls between redline and normal sporatically, but not everytime I drive. I've checked for air in the system and the fans work. Does anyone have any good idea what the problem is? Below is a detailed list of the symptoms that have occured in the past few weeks. Thanks for the input.

Day 1 (two weeks after installing everything): Temp gauge spiked up to redline just after being on the hwy for a few moments during the middle of a hot day in downtown LA with A/C on. I turned on the heater and watched as the temp gauge quickly went up and down between redline and normal operating temperature for the next several miles. Parked car and cooled it down for a couple hours. Returned to downtown LA and temp gauge sat at normal temp for 30 miles, then quickly went up and down for a few miles. Parked and the overflow reservoir rose from Full Cold to well over Full Hot.

Day 2: Ran the car with the cap off to burp the system, fans are working, and emptied the reservoir down to Full Cold. No leaks are visible. Everything seems to be working fine again


Days 3 through 6: (over a period of two weeks) drove car at different speeds and distance in LA without any symptoms. So I thought all was fine.

Day 7: The temp gauge begins to quickly rise and fall again in the afternoon while on the hwy down to San Clemente. Parked car and reservoir level looks fine.

Day 8: Topped off the radiator cap reservoir a little bit when the engine is cold. Drive 45 miles with the AC on and then the gauge begins to rise and fall quickly again. Once stopped, the overflow reservoir is completely full and spilling out. The car is parked and I am trying to figure out what to do next.
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Old 08-28-2012, 10:05 PM   #2
lavid2002
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How are you purging the system? Heat turned all the way on blower fan all the way up? Some people like to put the car on a slight incline to help air bubbles purge out. Stupid question, when's the last time the thermostat was replaced? Maybe it's acting up.

Have you purged cooling systems before? I hope you're not getting the car too hot as the head gaskets are easy to blow on these cars. Subarus do not like to be hot mayng.
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Old 08-28-2012, 10:43 PM   #3
BigJ02wrx
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I have not tried purging the system while running the heater all the way up and will consider that next time.

I spoke to a Suby mechanic today and he says it is the t-stat. I replaced the Subaru OEM with an Auto Zone/Kragen replacement, and those tend to give Subies problems. Now I wish I could replace the t-stat without losing any of the expensive blue Subie coolant from the system.
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Old 08-28-2012, 11:36 PM   #4
lavid2002
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I dunno if the '02s have those nifty little petcock valves on the bottom of the radiator. Maybe your new one has one. If it does you can drain out that coolant from the radiator with it. You will still get a large flow of coolant coming out when you pop that thermostat off the bottom of the water pump. Best you can do is try to catch most of it. No sealant on that thermostat gasket though, simply no needed and makes service a baish.

That heater core in your dash is essentially a small radiator transferring thermal energy from the cars engine to the air in the dash flowing by it via your engines coolant. If there are air pockets in that when you purge the system there will be air pockets in the cooling system.

Good luck, let us know how you make out. Also, remember an incline sometimes helps.
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Old 08-30-2012, 07:18 AM   #5
pr0d1gy ice
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I have had this same problem after replacing my coolant and putting new caps on. Burped the system several times. Each time i would find air pockets in the system. My problem has appeared to be a cracked oem radiator (started as a hairline crack and has grown larger.) I am replacing the radiator and thermostat next week so we will see but this would explain why i have air pockets in my system 1day-7days after burping. Good luck with this issue.
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Old 09-18-2012, 06:06 PM   #6
shooting
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napa makes a special overflow tank designed to fit over your radiator that lets you cycle the system with more coolant than it can fit, you cycle the fans a BUNCH of times and when they stop, plug this overflow bottle and seal the system. they take a bit to burp thats for sure, and use nothing but OEM t-stats! Id say change that for sure, iVe even had an OE stick closed and open on me, whatever it wanted to do, sounds similar to your situation. good luck.
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Old 09-18-2012, 06:17 PM   #7
theSTIgdrivesanSTI
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Are there bubbles or vapor in the coolant over flow tank? Sounds like it may be a headgasket issue. I was having exactly the same symptoms even after I replaced the radiator, tubing as well as tstat. But once I got the gaskets done the issue went away entirely.

Sorry man, welcome to the club
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Old 09-22-2012, 06:43 AM   #8
jaxscuby
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this could be a costly mistake.

burp the coolant properly or run risk of over heat
and kill your motor..
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Old 09-26-2012, 06:53 AM   #9
CBXJ
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I would change to the subaru t stat. Then fill with water and get all the air out. Then I would do a leak down test. In my experience, seemingly random temp spikes ( especially at highway speeds) point towards head gaskets.
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Old 09-26-2012, 06:07 PM   #10
shooting
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look for black flakey material in that overflow i told you about, if you see alot of chunks, it could be head gaskets, and... the bubbles will NEVER stop since the system is not sealed with a bad headgasket. so after you run the throttle a little you get some bubbles, if it keeps bubbling and they are tiny fish tank type bubbles then yeah signs say head G.
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Old 09-29-2012, 09:26 PM   #11
reid-o
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Be sure to replace the thermostat with the larger orifice especially if you have miles on your car. The temp of the thermostat is less a factor than the size of the element. The factory thermostat is much larger than most aftermarket ones.

If your fans come on and temp doesn't go down at idle with the car still it's a coolant flow issue. It's harder to diagnose when you're at speed between airflow and coolant flow.

Also check to see that once the car warns up that the top radiator hose has pressure from fluid and not air inside. Just squeeze it and you can feel if its ballooned from air. It will feel more like a balloon than a water bottle.

It depends on the miles of your car too. If you have miles and haven't replaced the water pump and used a smaller thermostat you may have reduced coolant flow from a dying pump plus maybe some air. I would replace with the correct size thermostat with temp of your choice and burp with the heater on like everyone is saying.
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Old 10-16-2012, 11:32 AM   #12
BigJ02wrx
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I had my local mechanic diagnose the problem. Blown head gasket

I went ahead and had the work done since there's only 70k miles on it and I don't know of any other Subaru I'd rather have.

Thanks for everyone's input.
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Old 11-12-2012, 08:48 PM   #13
sackytar
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Damn that blows
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