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My 1999 Subaru Legacy Outback, 2.5 engine, has been overheating recently. For a little while now my radiator has had a slight leak on the plastic piece where the return hose connects to the radiator and I added some K-Seal stop leak additive (not directly into the radiator but into the overflow reservoir) and for about a month the leak stopped unless I ran the AC. However just last Thursday on my way home I noticed what I thought was smoking coming from my engine bay, so I quickly stopped and shut off the engine, and when I popped the hood, I saw that it was evaporated coolant shooting out of the spot the leak was previously. Luckily I was about half a mile from home, so I let it cool off then drove it home with no more issues in that short distance.
Since then I tried changing out the thermostat and adding more coolant (which at this point can't be filled to the top or it leaks out the radiator, I assume the heat just made the leak worse, but still held near full of coolant) hoping that would at least get the car to be cooling again. But still idling for about 10-15 minutes the oil temp gauge starts to push off from the middle towards the high side, and from completely cool about a 5 minutes drive is enough to get the heat too high for comfort. Now the thermostat I put in was an OEM specified thermostat from NAPA auto parts, but some research has show people don't recommend that (although these were quite old posts) but I didn't see very much difference between the one I took out and the one I put in, maybe the tiniest bit of length difference.
Also to note, the radiator still doesn't leak when running, only when I add more coolant directly into the radiator. On top of that, with the heater at the hottest setting and full blast, I get comfortably cool air blowing out, whether driving or idling.
I do plan on replacing the radiator in the next few days because of the leak, but I'm afraid it won't fix the problem. I also read that head gaskets normally are an issue but when checking the oil, I don't see any milkiness to it, still looks fine. Another thing I read was the possibility of air being trapped in the heater core so fluid couldn't push through it, which I felt was a reasonable explanation since I'm not getting any heat through the vents. However when I tried to "burp it" there was still no hot air, and it was still over heating. Now the technique I used for burping was a little iffy however, as it was a youtube comment saying it was the method specified in the maintenance manual, but it did allow me to put more fluid in. I don't know if I just needed to do it more (fill it to the top, cap it, rev up to 4k rpm 4 times, shut off engine, wait a minute, repeat a total of 3 times then let it idle with heat at max) or if that method was even viable at all.
At this point I feel I've run out of options other than by passing the heater like I saw a post suggest, or just hoping that when I replace the radiator it all works out, but I was hoping I could drive about while I wait for the radiator to arrive like I have been (although maybe that's what caused it to get to this point).

Any tips or suggestions are truly appreciated, this car is nearing 370k miles on the motor and I would love to keep it going as long as possible since it has been driving quite well still, other than the heat issues I'm running into (and I guess a squeaking steering pump if I turn to hard but that's not game changing at the moment).
 

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Did the heat work before the T-stat change?
If so, I would say it's directly related to the thermostat not opening.
If the heat didn't work before the tstat change, I would say the leak stopper plugged it.

My bleed procedure is;
Park car with front up hill, or on ramps. You need the cap to be higher than the rest of the system.
Open cap, top off, burp the upper hose, top off, repeat until you can't get more in.
Start car, let it idle, heat on full blast. Top off as it bleeds.
I let it idle until fully warm and it no longer is burping itself, then i get in and slowly rev it a bit.
Usually just hold it at 2k for a few seconds, top it off, repeat.
 

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2005 OBXT Limited, VF37, STI intake, 5MT
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I assume this is in the United States, which would be an EJ25D.

Stop throwing parts at it and start saving for head gasket repair. Classic symptoms (no heat in cabin, ultra rapid overheating, can't seem to purge all the air, etc).

370k is pretty good, but don't keep running it hot. The 25D will eat the main bearings faster than anything with continual overheating.
 

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I assume this is in the United States, which would be an EJ25D.

Stop throwing parts at it and start saving for head gasket repair. Classic symptoms (no heat in cabin, ultra rapid overheating, can't seem to purge all the air, etc).

370k is pretty good, but don't keep running it hot. The 25D will eat the main bearings faster than anything with continual overheating.
From the sound of it, it's not going to be headgaskets. It sounds related to the initial radiator leak.
Usually when the headgaskets go, at least in my experience, the cabin heater blows very hot air.
This case, it sounds like the tstat is stuck closed, or the leak stopper plugged up something.
I would at least take the tstat out and test it in hot water, flush all the coolant, get that leak fixed properly, and see what happens from there.
 

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From the sound of it, it's not going to be headgaskets. It sounds related to the initial radiator leak.
Usually when the headgaskets go, at least in my experience, the cabin heater blows very hot air.
This case, it sounds like the tstat is stuck closed, or the leak stopper plugged up something.
I would at least take the tstat out and test it in hot water, flush all the coolant, get that leak fixed properly, and see what happens from there.
The failure mode for head gaskets in the BD/BG chassis is:

-loss of heat in cabin (due to combustion gases in the heater core)
-rapid and sudden over heating
-air bubbles in radiator when revving
-air bubbles in overflow
-overflow level rises during overheat but fails to lower after cooling down
-overflow level rises and coolant in radiator lowers and does not return to normal
-upper rad hose is hot and rock hard, lower hose is cool/cold to the touch

Of the ~50 Legacy/Outback/25D that exhibited these (and OP's) symptoms, ALL of them have been head gasket failures.

While adding stop leak generally does not help the cooling capacity, a clogged radiator generally shows as a slow overheat at highway speeds. Around town and low load, it can stay cool.

NAPA's OE-spec is the equivalent (and made by Stant) to the Subaru t-stat. If he paid near $20, it's the equivalent.
 

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Discussion Starter #6
The new radiator is going in today. Hopefully it does the trick, but as for the symptoms of a head gasket failure. @RoughDiamond I do have loss of heat, but as for the air bubble thing I'm unsure, and the overflow level hasnt changed in probably 2 weeks but I think that is the leak purging all the coolant that rises to the top, and the upper hose does getting blazing hot, but not hard. Ill admit I didnt think to check the lower hose...
@fcfordlord Not sure about the heat with the thermostat, I didnt test before I swapped (Now I will if I run in to this again I guess). I'll try out your bleed procedure and I hope you are right and it isnt a head gasket issue. I hope this thing is running today!
 

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2002 3.0 VDC Wag + 2018 2.5 Leg Ltd
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The new radiator is going in today. Hopefully it does the trick, but as for the symptoms of a head gasket failure. @RoughDiamond I do have loss of heat, but as for the air bubble thing I'm unsure, and the overflow level hasnt changed in probably 2 weeks but I think that is the leak purging all the coolant that rises to the top, and the upper hose does getting blazing hot, but not hard. Ill admit I didnt think to check the lower hose...
@fcfordlord Not sure about the heat with the thermostat, I didnt test before I swapped (Now I will if I run in to this again I guess). I'll try out your bleed procedure and I hope you are right and it isnt a head gasket issue. I hope this thing is running today!
buy a new OEM thermostat and a OEM rad cap,

plenty of overheating problems stem from the above 2 things, and on a new to you car reguardless of make, they are two things that should be swapped out right away so you know what is in there.

vs. old / wore out/ or aftermarket junk. (subaru thing work at specific temps and pressures in metric,)

and not all radiators take the OEM cap. (one that does is CSF ...found in catalogs like summit etc).

_________

but: if what you got there is already gone,....and many EJ25D are goners when bought.

you can go from the worst engine the company made to one of the best with this thread:
https://www.subaruoutback.org/forum...248329-ej22-swap-into-ej25d-dohc-vehicle.html

just need to carefully select the right drop in EJ22, and not all are the right ones.

edit: and a FYI for respondents, this is a US spec 99 based on IP.
 

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Discussion Starter #8
Update! I installed the new radiator and everything seems to be running fine again! Heat is blowing out again, and the oil temp gauge stayed slightly below half during about a two mile drive (after an idling to mid temp gauge). Also thank god the radiator was a CSF like you suggested @eagleeye, because I didnt even think about the fact that it wouldnt come with a cap, but the one I already had fit just the same. Will let it cool off then going to try a further and faster drive later. Ill post again if any problems come up. Thanks all!
 

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1. it started to leak. fix the leak.
this is about as simple and logical as you can get.

lack of heat and overheating were just symptoms of air in the cooling system from the leak or improper bleeding.

if you want to get into heagaskets - you need to top the radiator off, properly burp the cooling system and report what happens then.
 
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