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Old 10-10-2017, 08:19 PM   #1
jrinker
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Default 2.5L 2007 Keeps overheating tried nearly everything?!

about 3 months ago my 2.5L Subaru overheated, I assumed it was a thermostat because the recovery box was filling up, I replaced the thermostat and it ran fine for about a month. Until it randomly started overheating again.. keep in mind about 30k miles ago I had the head gasket replaced.

It will randomly run for about 200-250 miles give or take then it will overheat and fill the recovery box full even to the point that the cap pops open to relieve the pressure.. UNTIL I fill the radiator up and burp it for 10-20 mins then it will run another 200+ miles then overheat again... repeat!

I tore out and replaced the radiator, thermostat (again) checked all hoses, took out the water pump and made sure everything was working with it (fins, gear)
I used a pressure tester on the radiator and it seems to slightly leak at 10PSI but will hold somewhat steady at 5psi, but I can't hear any leak?? head gasket again? The oil isn't foamy or chocolate like in color, the exhaust isn't blowing out any wet fumes..

I am stumped? I feel like it's getting air somehow into the system after a few hundred miles and air locking it which is making it overheat? OR the head gasket is bad? intake gasket is bad?

Any advice please it's driving me nuts!!
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Old 10-10-2017, 11:50 PM   #2
Valarius Starchaser
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The system is under 13psi I believe with the stock rad cap if 10 can't hold them obviously the caps going to cause an issue

Your not noticing any on the ground or fumes? Any other recent work? I did an engine swap recently and left one clamp loose causing a boil over on days above 75 on drives for longer then 20 minutes which is pretty rare for me

Maybe an end tank seal on the radiator went bad

Kind of an interesting problem
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Old 10-11-2017, 09:47 AM   #3
Samurai Jack
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Or maybe you have the wrong radiator caps or the right radiator caps in the wrong places?

Are you using OEM radiator caps?
Which cap is on the radiator and which cap is on the expansion tank near the turbo?
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Old 10-11-2017, 10:33 AM   #4
Charlie-III
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During all this, are you keeping an eye on the overflow tank? If you have a small leak, the system should pull coolant from the tank as it cools off. If you run the tank dry, you pull in air which could cause your issue. Keep the tank proper, things should be OK.

Note, I recently found an issue on one of our engines, sounds like your issue. The problem was the rubber hose to the overflow, it had a hole in the bottom so instead of pulling coolant back in, it pulled air. The hole was where the hose ran over a radiator fan bolt. Likely we leaned on it enough to cut the hose.
It's been fine since a couple layers of electrical tape over the hose since it's only a siphon hose.

As to other ideas, yes, sounds like old/weak caps. I believe the round cap is on the radiator, the one with wings is on the upper tank.
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Old 10-11-2017, 10:53 AM   #5
Norskie
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I'd suggest you test the coolant for hydrocarbons (the Napa test); if only to confirm or rule out a head gasket leak (yes, they can leak w/o muddying the fluids).
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Old 10-12-2017, 08:31 PM   #6
MedicDG
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Quote:
Originally Posted by jrinker View Post
about 3 months ago my 2.5L Subaru overheated, I assumed it was a thermostat because the recovery box was filling up, I replaced the thermostat and it ran fine for about a month. Until it randomly started overheating again.. keep in mind about 30k miles ago I had the head gasket replaced.



It will randomly run for about 200-250 miles give or take then it will overheat and fill the recovery box full even to the point that the cap pops open to relieve the pressure.. UNTIL I fill the radiator up and burp it for 10-20 mins then it will run another 200+ miles then overheat again... repeat!



I tore out and replaced the radiator, thermostat (again) checked all hoses, took out the water pump and made sure everything was working with it (fins, gear)

I used a pressure tester on the radiator and it seems to slightly leak at 10PSI but will hold somewhat steady at 5psi, but I can't hear any leak?? head gasket again? The oil isn't foamy or chocolate like in color, the exhaust isn't blowing out any wet fumes..



I am stumped? I feel like it's getting air somehow into the system after a few hundred miles and air locking it which is making it overheat? OR the head gasket is bad? intake gasket is bad?



Any advice please it's driving me nuts!!


Rule out head gasket again! Would would buy and do a Subaru head gasket test just to rule it out.
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Old 10-13-2017, 08:45 PM   #7
Monteee
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I had the similar issue and my coolant was leaking into my turbo.
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Old 10-13-2017, 09:06 PM   #8
hondaeater69
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sounds like head gaskets to me.
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Old 10-13-2017, 11:19 PM   #9
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Quote:
Originally Posted by hondaeater69 View Post
sounds like head gaskets to me.
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Old 10-13-2017, 11:26 PM   #10
hondaeater69
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you don't have to tell me

i've done that test on every subaru my family has owned. and we've never even had a bad HG
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Old 10-17-2017, 12:29 PM   #11
flup
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Theres a chance you're running lean, which tends to burn much hotter than running rich (after owning several classic cars that overheated I figured out this was the problem on my vintage bmw). Get a bluetooth OBD2 reader and use your favorite smartphone app to check your mixture on the highway.
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Old 10-17-2017, 02:43 PM   #12
mrsaturn7085
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When you had the head gaskets replaced 30k ago, what was the cost of the repair? Anything less than $3,000 probably didn't include the required machine work and coincidentally, 25-30k is usually about all you get out of a head gasket repair that was performed half-assed by skipping this step.

If your overflow tank is completely full, that's like a 95% or better telltale sign of a bad head gasket.
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Old 10-23-2017, 06:16 AM   #13
Donjoshuason
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Check overflow tank on radiator. If its empty or overfull you'll get air in the system.
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Old 10-23-2017, 06:19 AM   #14
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Quote:
Originally Posted by Donjoshuason View Post
Check overflow tank on radiator. If its empty or overfull you'll get air in the system.
You might need to drive it for a couple of blocks and it will go to the red on the temp. But park it let it cool all the way and then restart. Shouldn't overheat after that. Much cheaper than heads. Lol
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Old 10-23-2017, 12:04 PM   #15
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Quote:
Originally Posted by Donjoshuason View Post
Check overflow tank on radiator. If its empty or overfull you'll get air in the system.
This is not correct. If it's empty, yes, you'll suck in air; if it's completely full when you shut the engine off (as it, up to the brim), it's almost certainly head gaskets.
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Old 10-23-2017, 05:58 PM   #16
Charlie-III
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Quote:
Originally Posted by mrsaturn7085 View Post
This is not correct. If it's empty, yes, you'll suck in air; if it's completely full when you shut the engine off (as it, up to the brim), it's almost certainly head gaskets.
Agreed.

If it started about 1/2 full and then overflows, HG is the most likely suspect.

As I have stated before, I never saw oil/coolant mix (in coolant or oil) in ANY blown Subaru HG I have seen.
Overfull overflow tank is sorta a sign.
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Old 10-23-2017, 06:26 PM   #17
mrsaturn7085
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I've never seen oil/coolant mix in a HG failure ever. You generally get a positive result on a combustion gas chemical test, though.
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Old 10-23-2017, 06:37 PM   #18
Charlie-III
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Quote:
Originally Posted by mrsaturn7085 View Post
I've never seen oil/coolant mix in a HG failure ever. You generally get a positive result on a combustion gas chemical test, though.
I will admit, I have never done a HC test, overfull overflow bottle or a "cooling pressure tester" test usually gets me there.
I have posted before how I use it.

Either method is a fairly good example of when to do HG's.
Just saying.

I work with what I have, maybe I need even more stuff......
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Old 10-23-2017, 08:29 PM   #19
mrsaturn7085
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Well the chem. test sometimes gives false positives, so I personally probably won't restock when I run out of the liquid... but it lasts forever. If you manage to get through a full bottle and you don't run a shop, you should probably just quit cars altogether.
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Old 10-23-2017, 09:02 PM   #20
yeszerd
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My wrx overheated a while back and same thing like you just kept overheating and I tried everything I could think of including HG tests, thermostat, coolant pressure test, hoses, and spent hours burping the system. Coolant would keep overflowing in the overflow. Long story short just replaced mine with a jdm motor after my last motor soon after skipped some teeth on the timing belt. Still haven't opened up the motor to see what was up with it but I'm betting it was something internal.
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Old 10-24-2017, 10:13 AM   #21
Charlie-III
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Quote:
Originally Posted by yeszerd View Post
My wrx overheated a while back and same thing like you just kept overheating and I tried everything I could think of including HG tests, thermostat, coolant pressure test, hoses, and spent hours burping the system. Coolant would keep overflowing in the overflow. Long story short just replaced mine with a jdm motor after my last motor soon after skipped some teeth on the timing belt. Still haven't opened up the motor to see what was up with it but I'm betting it was something internal.
The pressure test is a little different. Install tester, start engine, let it warm.
As it does, pressure will rise due to heat, but the rise is slow. Eventually it stops rising if everything is OK.
A bad HG will make it rise fast and you have to keep bleeding the pressure off.
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Old 10-24-2017, 11:59 AM   #22
mrsaturn7085
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The other thing to remember is that a bad head gasket on a turbo motor may only show symptoms under boost when cylinder pressures peak. This is why you lose fluid while you drive but rarely see the overflow actually... overflowing. Generally, a chem. test will still show positive, however.
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