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Old 07-02-2020, 01:56 PM   #1
Scooby Newbie
Member#: 408391
Join Date: Dec 2014
Location: Colorado
2015 WRX STI Limited

Default Very small bubbling more like fizzing from upper radiator

So i have a 2015 Subaru WRX STI Modified with 57000 miles
-Blouch Turbo
-1050x Injectors
-TGV Delete
-Catless DP, Invidia Exhaust
-GrimmSpeed TMI
-Killerb oil pickup and oil pan
-ACT Clutch and flywheel
-Cobb SF Intake
-Walbro Fuel Pump

probably other stuff im forgetting

Anyways my issue (or hopefully non-issue) is i went to burp the coolant system today, not because of temperature issues but more just to stay on top of it (and i heard like a grumble after shutoff the other day kinda like a stomach ache) I noticed that there were very small bubbles like when you see other posts they mention dime size bubbles but im getting even smaller its almost like a soda fizz. This happens from cold start and tends to slowly dissipate as it reaches Operating temps. I've never really tried burping the system before aside from like one other time a year ago and i recall actually it doing the same fizzing thing. I've only added maybe idk 1/8th of a coolant bottle to the car in a year maybe less, coolant reservoir always between Low and Full never over, coolant has no odd smell or foreign substance in it from what i can tell, no milky oil and i mean i burn maybe half a quart in close to 3,000 miles with "spirited" driving but never really beating the piss out of it. Also worth mentioning i live in western Colorado where summer ambient temperatures are consistently 100 degrees and its at 4500 elevation and ive only seen my coolant temp go over 200 one time and it dropped right back down soon as i saw it. I suppose my fear is HG failure but i have like literally 0 symptoms besides the tiny bubbles in the upper radiator. Car runs great pulls great starts right up. But every forum i see with anything regarding this has more severe symptoms and is like "BLEW YOUR HG GOOD LUCK" any feedback is appreciated.
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Old 07-02-2020, 03:56 PM   #2
Scooby Newbie
Member#: 408391
Join Date: Dec 2014
Location: Colorado
2015 WRX STI Limited


Also if wrong thread will someone move it? I seem to have a hard time navigating these forum pages
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Old 07-30-2020, 04:02 PM   #3
Scooby Specialist
Member#: 132389
Join Date: Nov 2006
Chapter/Region: BAIC
Location: SF Bay Area

I would not worry about it until coolant starts to fall out from the coolant expansion/overflow tank next to the radiator.
Also, depending on how the HGs fail (if they fail), you may never get or see coolant in the oil (which is a blessing); you'll probably get some oil droplets in the coolant.
There again, these oil droplets will accumulate, over time, into the overflow tank.
All of these symptoms takes time to fully develop; initially, coolant started to overflow only when I was at the track after a full 20~25 mins session.
Then, it started happening after 15 mins of hard driving into the canyons and backroads.
Then, after a year or so, it happened after a 3rd gear pull to redline; a coolant hose to the turbo got loose. Put the hose back on, topped off radiator and drove back home.
I had lined-up all the tools and equipment I needed to do the job; I pulled the engine and did the work on my own.
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