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Old 08-01-2020, 04:32 PM   #1
atomicsubi
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Question Could it be the radiator cap?

Howdy, I'm coming out of lurking mode to share a puzzler. I just finished a headgasket job and I'm overheating and it's driving me nuts!

Background- 2006 WRX, just did headgaskets and other stuff since I was in there like new flywheel, clutch, valve job, etc but this story is about overheating. Part of this job was replacing most everything I had my hands on to be proactive so the cooling system is almost all brand new but I'm overheating.

Replaced- Headgaskets, radiator, water pump, thermostat, hoses (the main ones), EDIT TO ADD: also had heads resurfaced by the shop

Issue- It overheats after about 5 minutes of driving, not while idling in garage. I've just spent 1.5 days burping air out but have failed. Day 1 I used a regular funnel on the top tank and it worked ok I thought but after burping, cool down, test drive/repeat I got nowhere. Day 2 (today) I bought one of those fancy funnel kits and used it on the top tank again. I ran the car for over an hour and tried all the stuff everyone says to do including things people don't...such as squeezing the bottom and top RAD hoses. No luck!

Observations- while using the big fancy funnel, my fluid level dropped over an inch which seems good because I'm displacing a bunch of air. But it seems like I'm pulling air in somewhere because I'm burping like hell and just can't get the air out. I even did the combustion gas test 3 times and it was negative each time. I tested it by the tailpipe and it turned yellow so I trust it. The circuit seems to be flowing fine, thermostat opening.

Next?- The whole cooling circuit is replaced except the radiator caps. So I have to wait until Wed to get them from my local Subie dealer. I'll try that then I guess it's leakdown test time and compression. These should be ok since the air I'm pulling in isn't combustion gas but I'm out of ideas. Also, looked for cracks in block and head couldn't find any when it was apart, shop that machined the heads and did valve job didn't see any.

So back to the thread title. Could it be the radiator cap pulling in air? I'm purging air like mad while the cap is just sucking it right in?
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Last edited by atomicsubi; 08-01-2020 at 07:00 PM.
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Old 08-01-2020, 04:47 PM   #2
subaru_gc8
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did you resurface he head before puting it back together?
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Old 08-01-2020, 06:59 PM   #3
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Originally Posted by subaru_gc8 View Post
did you resurface he head before puting it back together?
Great question and I will add that above. Yes, had the shop do it and I should also mention it wasn't warped from before which suggests to me that the engine wasn't run too hot and makes it even less chance of a cracked block.
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Old 08-01-2020, 07:03 PM   #4
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I'm pretty much down to the radiator cap, has anyone had actual experience with this pulling air in?
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Old 08-01-2020, 09:33 PM   #5
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yeah see if that is the problem it cant hurt and its a pretty cheap fix if it turns out to be that
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Old 08-02-2020, 12:18 PM   #6
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FWIW, I replaced both caps on my cars at 10 years old. its cheap insurance.

The rubber seals on the old caps, were less then perfect.
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Old 08-02-2020, 04:40 PM   #7
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Update, just bled it again and test drove. It ran hot but when it got close to red on the gauge, I turned on heater and it would run cooler. I kept trying it with and without heater and sure enough with heater everytime it ran around 50-70% on gauge.

I wonder if I have some clogged up lines still from the problem before I took it apart. It had a lot of oil in the coolant so now I guess I need to flush the heck out of it.
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Old 08-03-2020, 01:21 AM   #8
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The forester I just got started running hot yesterday, it was extremely hot out though I swapped the cap today because the one on there wasn't even properly seated and came off so easily. Seems to run cooler but I feel like i have headmaster issues amongst ringland failure.
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Old 08-05-2020, 10:06 PM   #9
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New caps on today, still runs hot. The mystery continues...
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Old 08-08-2020, 01:53 AM   #10
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i know this sounds like a dumb question but have you made sure your fans are turning on in both stages, low and high?

How are you verifying it it overheating? just by your dash gauge? You need a scan tool or something to watch a digital number.

I have had bad thermostat and the car was warming up as it should but in normal driving mode i noticed it was staying about 10 degrees higher that normal and the car would eventually throw a code because the fans running were not bring the temp down.

With a car idling it will take a long time for it to trip the fans due to the radiator simply having coolant going through it, the radiator can radiate more heat than the engine creates with no load.

Was the thermostat put in in the correct orientation? Meaning the jingle bleed hole at top.

If you keep "bleeding it" are you loosing coolant?
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Old 08-08-2020, 02:24 AM   #11
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Have you confirmed the new thermostat is good? It you put it in a pot of boiled water it should open up.
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Old 08-09-2020, 05:37 PM   #12
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Quote:
Originally Posted by SlammedSix View Post
i know this sounds like a dumb question but have you made sure your fans are turning on in both stages, low and high?

How are you verifying it it overheating? just by your dash gauge? You need a scan tool or something to watch a digital number.

I have had bad thermostat and the car was warming up as it should but in normal driving mode i noticed it was staying about 10 degrees higher that normal and the car would eventually throw a code because the fans running were not bring the temp down.

With a car idling it will take a long time for it to trip the fans due to the radiator simply having coolant going through it, the radiator can radiate more heat than the engine creates with no load.

Was the thermostat put in in the correct orientation? Meaning the jingle bleed hole at top.

If you keep "bleeding it" are you loosing coolant?
Hey yes the fans are working. Thermostat was new and installed with the hole on top. I have flow but maybe not enough. When I drive it will overheat unless I have the heater fan on, then it runs around 50% hot on the gauge.

I sent it to a little Subaru shop I'm waiting to hear back. The entire cooling circuit is new except a couple hoses, maybe there is still some sludge in those blocking full flow or I have a bad thermostat. I bought the thermostat from napa and who knows...it could have been a returned one or someone put the wrong one in the box. Also, I'm using the dash gauge but when it shows hot it is correct because the hoses are extremely hot and engine is running very rough until temp comes down. The gauge appears to be accurate.

Bleeding = yes I have bled until the level quit dropping. But everytime I squeeze the hose, I get bubbles so I can't figure out if that's normal or if I'm getting air from somewhere? It's actually driving me crazy at this point and making me question everything LOL. I probably did something stupid and the shop is going to figure it out.

Last edited by atomicsubi; 08-09-2020 at 05:46 PM.
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Old 08-09-2020, 05:42 PM   #13
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Originally Posted by nikau View Post
Have you confirmed the new thermostat is good? It you put it in a pot of boiled water it should open up.

Not yet but I can tell it's opening. I have flow, cools down with heater fan on, and bottom radiator hose gets cooler after fans come on and flow begins. But I'm wondering if it is not opening enough.
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Old 08-09-2020, 06:00 PM   #14
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Quote:
Originally Posted by atomicsubi View Post
Hey yes the fans are working. Thermostat was new and installed with the hole on top. I have flow but maybe not enough. When I drive it will overheat unless I have the heater fan on, then it runs around 50% hot on the gauge.

I sent it to a little Subaru shop I'm waiting to hear back. The entire cooling circuit is new except a couple hoses, maybe there is still some sludge in those blocking full flow or I have a bad thermostat. I bought the thermostat from napa and who knows...it could have been a returned one or someone put the wrong one in the box. Also, I'm using the dash gauge but when it shows hot it is correct because the hoses are extremely hot and engine is running very rough until temp comes down. The gauge appears to be accurate.

Bleeding = yes I have bled until the level quit dropping. But everytime I squeeze the hose, I get bubbles so I can't figure out if that's normal or if I'm getting air from somewhere? It's actually driving me crazy at this point and making me question everything LOL. I probably did something stupid and the shop is going to figure it out.
50% hot as the Guage is dead center? Cold is 0% and the Hot mark is 100% i would think 50% is dead center.

The fact that you turn your heater on and it cools down tells me that the car is not getting enough cooling from your fans.

Also its not good to go off my hoses feel hot so I belive its hot. A 200 degree hose is not something your gonna be able to touch and that would be normal Temps.

Also I would not be so worried about the bubbles as long as its small. The car can self bleed air as you drive as long as its not a large amount. When bleeding are you only idling it or are you holding a rpm at like 2k consistently?
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Old 08-10-2020, 10:03 AM   #15
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50% hot as the Guage is dead center? Cold is 0% and the Hot mark is 100% i would think 50% is dead center.

The fact that you turn your heater on and it cools down tells me that the car is not getting enough cooling from your fans.

Also its not good to go off my hoses feel hot so I belive its hot. A 200 degree hose is not something your gonna be able to touch and that would be normal Temps.

Also I would not be so worried about the bubbles as long as its small. The car can self bleed air as you drive as long as its not a large amount. When bleeding are you only idling it or are you holding a rpm at like 2k consistently?
Yes halfway on the gauge. When engine is under load (driving), gauge goes to red. If I turn on heater, gauge comes down to around 50%.

When idling, temp climbs on gauge, fans come on, temp goes down and gauge reads near the bottom 1/3 line which I believe is normal. The fans go through a normal on and off cycle and the gauge changes accordingly.

Bleeding (burping) air has been done by idling, revving, squeezing top and bottom hose, cooling down/repeating, driving then repeating, rinse/repeat ad nauseum.

This is why I took it to the shop because I can't read actual temp and can't verify that the sensor, gauge, thermostat are working properly. What I can do is run a series of experiments and eliminate variables which has so far failed me. I am a very mechanically "capable" person, but I think this needs to be hooked up to diagnostics that I don't have. I started posting here to see if there was anything that I might have missed that is unique to this engine but it seems by the responses that I have covered all the bases possible without diagnostics. I should hear back soon from the shop.
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Old 08-12-2020, 03:09 PM   #16
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Make sure you didn't put the thermostat in backwards. Don't ask me how I know Took me 3 days to figure out why my radiator funnel was burping like crazy
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Old 08-13-2020, 10:42 AM   #17
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@atomicsubi. Sorry you're having issues.

I am always at a loss when I read about others having issues with cooling and them having to burp their system to purge air.

3 subarus, (2 in the garage now), 175K and plenty of coolant / hose / waterpump / thermostats changes over the last 13 years and I have never had to burp a car. Do you have accumulated air everytime you are running the car? I don't get any bubbles when I squeeze an upper or lower hose. Cold or hot.

Did you use an OEM thermostat? That alone has always proven to be one of the most common root cause problem areas. I always use OEM parts for cooling system, hubs and the like as having to take something apart again really bites.

Unfortunately '04~'07's are known for premature headgasket failures and are known for usually needing at least one replacement during an engines life. Subaru for the most part fixed this starting in '08. Next came a higher than average number of ringland failures in '12~'14's. Once again Subaru stepped up in 2015 and things improved, but still not 100% reliable.

Did you use OEM headgaskets. I hate to harp on OEM, but there have also been a large number of people who used something after market and if not properly aligned 100% can block a passage just enough to cause an overheating situation under certain conditions. So I do hope that you used OEM parts for the repair as this does decrease the likeyhood of problems.
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Old 08-13-2020, 10:24 PM   #18
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Very interesting issue
Please keep everyone posted

Not that this will fix issue
But I was so sick and tired of burping system And bubble still present
I went Viking
Not only I backed car on inclined drive way, But put 2X4’s behind rear wheels, jacked car up by front subframe And burped and burped
Freakin 45mins
Seemed to work

Last edited by AliBenn; 08-13-2020 at 10:27 PM. Reason: English
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Old 09-07-2020, 06:16 PM   #19
atomicsubi
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Thanks for the replies, I don't come on here often and it's time for an update. Great question on the gaskets, yes I used OE.

I sent it over to a local Subaru shop, the same shop that did my valve job and machined the head surface. The shop owner is convinced that I have a problem in the block, he thinks it's likely warped. I put a straight edge on it and checked with a .015 feeler but maybe I made a mistake...not sure. But he checked everything over and has narrowed it down to that and I have to agree because of everything I posted above - the coolant circuit is functioning and is all new.

So, I guess I'm pulling the motor again. I'll get in there and look everything over then decide what to do. I might be shopping for a built shortblock soon. Crawford Performance has an OE built one for $2k that I've been eyeing up. I'm open to suggestions...
Cheers
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Old 09-07-2020, 06:17 PM   #20
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Quote:
Originally Posted by 3-MPG View Post
Make sure you didn't put the thermostat in backwards. Don't ask me how I know Took me 3 days to figure out why my radiator funnel was burping like crazy

Dang!
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Old 09-07-2020, 08:19 PM   #21
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Are the caps reversed? Do you have the radiator cap on the reservoir and the reservoir cap on the radiator? That can definitely cause problems.
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Old 09-07-2020, 09:14 PM   #22
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Are the caps reversed? Do you have the radiator cap on the reservoir and the reservoir cap on the radiator? That can definitely cause problems.
No sir, caps are correct location and brand new OE.
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Old 09-08-2020, 06:53 AM   #23
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Do you have OEM fans?
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Old 09-09-2020, 08:36 PM   #24
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Hmmmm
Pull the plugs
If they are wet/rusty.....something went wrong with HG replacement or machine shop
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