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Discussion Starter #1
I come here seeking the knowledge and wisdom of the Subaru Outback savants. 3 trips to the Subaru dealer have been fruitless. They can find no answer for my overheating problem. Give me some guidance and I will be eternally grateful. Or at least my wife will be. It’s her car.

Sorry if this is a bit long. Lots of items to cover.

My car is a 2011 Outback Premium 2.5L, purchased new. The car currently has 69K miles. The car has been fantastic, pretty much no issues. Never wrecked. About 2 months ago I was driving and I notice the engine temp light come on. Just normal driving, nothing aggressive. Knowing the engine is all aluminum, I don’t want to take any chances, so I have it towed to the dealer. They eventually tell me I have a cracked radiator which cost about $675 to replace. I found this really hard to believe because like I said, never had any issues, never overheated before, and never any wrecks or fender benders. A radiator just going bad at 65K miles? Whatever. I guess it’s possible. I pay for the work and am on my way.

About 3-4 weeks later, the same problem occurs – engine temp light comes on. I pop the hood and smell coolant. No system leaks, but I can see that the coolant is being blown out through the overflow tank. After a cool down, I drive it to the dealer for them to have a look. During a long uphill stretch of interstate, the temp light comes on again. I baby it and eventually the light goes off. I get close to the dealer and for the first time, it starts flashing. Then it goes out. After a day of looking at it, the dealer thinks that maybe there was an air bubble in the system that was introduced during the radiator service. They top it off and bleed the coolant system. They tell me they can find no problems and I’m on my way. No charge.

I have been keeping a close eye on the coolant by watching the level of the overflow tank. Every time I checked, it seemed normal. The car is doing fine. No issues. Until this week. Engine temp light comes on again.

Opening the hood, I smell and see coolant. Again, blown out of the overflow bottle. The bottle is now empty. This time, before driving the car to the dealer, I get some of the ($23 per gallon!) blue Subaru coolant I half-fill the overflow tank and top off the radiator. I put the car on ramps and run it to temperature. I squeeze the upper hose to assist bleeding any air out of the system. I didn’t want to overheat again on the way to the dealer. I drive it there with no issues. After a day of looking, the dealer can find no problems. The Service Adviser said they had their senior tech look at it, along with the service manager. They pressure test the block AND the coolant system. Everything checks fine. No indication of pressure loss. There are no codes in the computer and no indicator of overheating. They tell me they cannot find anything wrong. Again, no charge from the dealer.

While driving a couple of days before it overheated again, I hear a bit of gurgling inside the dash. Sounds like air in the coolant system. Maybe I should have paid more attention to it. But I had heard this sound plenty of times before in the 4 years I have owned it. And it never overheated before.
I’m guessing air must be getting introduced into the system, but I don’t know how. The dealer says it passed the pressure checks fine. And why isn’t a code being set in the computer? The temp light has definitely been on. Does it need to hit a certain threshold before a code is set? Can the temp light come on without setting a code? What does it means when the temp light flashes vs. just staying on?

The car is driveable now, but I can’t say I trust it. I’m guessing it’s just a matter of time before it overheats again. I really questioned the dealer about the radiator replacement as to if it was really needed. He swore to me it was cracked and he said he saw it himself. Unfortunately, I never asked to see it.
Any of you gurus out there got any ideas of what to check? I really need to be able to depend on this car. And right now, I can’t.
 

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Discussion Starter #3
No, it hasn't. I did inspect it closely and it looks perfect (for what that is worth) The dealer has pressure checked the engine twice. I assumed they tested the cap too. They must have tested it, right? Isn't that the first thing you would check?
 

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You'd be surprised...

No they probably didn't. Though on a 2011, that likely isn't the issue. It would be a quick cheap test though.

You either have a very small leak that is hard to detect or you might even have a bad head gasket.
 

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Test for a cap is typically a visual inspection.

Most system pressure testers take the form of a replacement radiator cap- meaning you remove the cap, install the tester tool in its place and read the result. So the cap isn't installed during that test. Then, they look at the cap (hopefully) and reinstall it.

Cap is a fair bet, the way I read this.
 

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I am going to say you need to try a cap. My XT was getting air sucked into the system...only during a short period during cool down. Air was passing by the cap, after the car had mostly cooled down. It was perplexing enough that I was even concerned about an HG...almost unheard of the XT motor.

I changed both caps...(header tank on the turbo) and had no problems. I now have a Mishimoto radiator. I am running the cap Mishi gave me until there is some reason not to. I run the stock OEM on the header tank.
 

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Even though there were days or weeks without the overheat warning light coming on, it doesn't necessarily mean that the engine wasn't running on the unusually hot side. I haven't found any specs indicating at what temperature the light will come on but I suspect that, if it's like other warning lights of the same genre, it's probably well beyond the "normal" temperature range, which itself is quite broad.

I wonder if the dealer hooked up the Subaru Select Monitor, or a similar scanner, and checked the actual engine coolant temperature in a variety of driving situations (similar to how the car is used) to see where where it averaged at and how much it varied. The thermostat could be faulty.

But what about the fans? When the temperature warning light was on and the hood was opened to have a look, were both radiator fans running at high speed?

There's no diagnostic trouble codes specifically for "overheating" -- that's left up to the engine coolant temperature warning light.

Pages 3-13 and 3-14 of the Owners Manual explain the coolant temperature warning light flashing versus being on steady.
 

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I am fairly new to Subaru. I agree with the suggestions about the cap and the fans. Also, I assume Subaru engines have a thermostat in the cooling system. Thermostats have typically been the problem I have had when I experienced overheating engines in other brands. This is typically a low cost DIY fix.
 

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Even though there were days or weeks without the overheat warning light coming on, it doesn't necessarily mean that the engine wasn't running on the unusually hot side. I haven't found any specs indicating at what temperature the light will come on but I suspect that, if it's like other warning lights of the same genre, it's probably well beyond the "normal" temperature range, which itself is quite broad.

I wonder if the dealer hooked up the Subaru Select Monitor, or a similar scanner, and checked the actual engine coolant temperature in a variety of driving situations (similar to how the car is used) to see where where it averaged at and how much it varied. The thermostat could be faulty.

But what about the fans? When the temperature warning light was on and the hood was opened to have a look, were both radiator fans running at high speed?

There's no diagnostic trouble codes specifically for "overheating" -- that's left up to the engine coolant temperature warning light.

Pages 3-13 and 3-14 of the Owners Manual explain the coolant temperature warning light flashing versus being on steady.
I will support this 100%. I have both the stock temperature sensor and an aftermarket gauge. As well as an oil temperature gauges...all with numbers. Not a blind gauge like on the dash.

If you spend anytime logging data...or in my case watching the gauges...that gauges on the dash is pretty dumb. I din't know about the newer cars with the temperature light. Temperature variation are actually pretty dramatic....while that gauge sits at 9:00 just happy as ever.

And most of the time, when it decides to peak...it is late in warning you...it basically says...I'm Hot...oh sh*t...Really HOT....Too HOT.

:9:
 

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Oh man this sounds crazy. Will you promise to post back with the final solution!?

Every time it's overheated has it been during a similar condition - such as idling, driving up a hill, coasting, first start, after driving a long time, at highway speeds, etc?
When it starts running hot - are the fans running?
Sticking thermostat? this seems really, really unlikely....

Ideally what would be good to know if this is being caused by low coolant or not:
1. is the fluid low when it first starts to overheat?
2. are there bubbles in the overflow tank just prior to or when it starts to overheat?
(this is tricky because i mean just small bubbles - not boiling due to overheating - normally this is easy to test because you have an actual temperature gauge - can see the temp rising - and check before it's actually overheating).

3. if you can get it tested while overheating - they should test for exhaust gases in the overflow tank/coolant - that would indicate a headgasket failure.

Maybe you need to get a bluetooth OBDII adapter and just have a continuous coolant temperature read out feeding your phone so you can answering some of these questions.
 

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Discussion Starter #12
OP here... I suppose I should go ahead and replace the cap. It makes sense as it is probably the least expensive item to replace. Is there any need to stick with OEM? I would think an aftermarket cap would be just fine, but if somebody differs, please speak up. After overheating, the first thing I checked was the fans. They were running just fine. There doesn't seem to be any issue with those. Thanks to all who have offered suggestions. I will post any new developments here.
 

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Given the time span between events it sure sounds like air getting drawn ito the system then a air bubble which causes the flow to stop circulating. Cap Subaru only replacement. Check the hose in the over flow can a number of yrs ago Subaru issued a note that the hose should get the end in the bottom of the overflow can clipped at a 45 degree angle. They started seeing cases wher it would suck down to the bottom of the can then the cap would break seal and draw air into the system.

I would start checking it daily after cooling off to see if the level under the cap has dropped. A leaky heater hose or valve could cause this too.
 

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My 2010 just hit 70k same exact set up and engine as yours. Zero issues so far. Possible the water pump has an odd flaw and could be the issue but, that would be a really rare and strange failure at such a low mileage.

As for cooling system stuff only use OEM parts. Subarus are famous for being very picky about caps, tstats and water pumps and the stock gear typically is very good and rarely ever causes issues.
 

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I would be very surprised if it's the cap.

Subaru cap should be used. if you installed an aftermarket - even if it just happened to be a problematic cap the statistical chances of it having the same identical issues would be astronomical. All that to say - it's not the cap, doesn't matter which you try - but sure go ahead for the cheap and simple hail mary.

Mail me your old cap, I'll put it on another Subaru and run it.
 

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Sounds like an internal HG leak to me. The overflow filling and puking coolant is the giveaway. Also, it occurring when going uphill is a giveaway as well.

When you went to the dealer your system was probably low on coolant and there was most likely coolant on the radiator from the the excess coming out of the overflow, hence the cracked radiator diagnosis.

Test for the presence of exhaust gas in the coolant, more commonly known as a block leak test.
 

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Well - any significant leak in the system and you can't hold pressure - if you can't hold pressure, the coolant can boil (you rely on the system pressure to elevate the boiling point). (for your initial radiator failure, it's not uncommon for them to leak at the seal between the metal core and the plastic end tanks) - one thing to check - is the thermostat opening when it should? The cooling system isn't very complicated - there's the thermostat, the radiator, the water pump, and then the heater core. For the water pump, a bad pump usually leads to issues when sitting still, not when driving at highway speed. A sticking thermostat could cause a problem intermittently, though...

If they pressure tested the system, then you probably have no leaks, other than potentially the radiator cap.
 

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A stuck thermostat can cause overheating.
Low coolant level can cause overheating.
Radiators cannot generate pressures by themselves.
Engines can however.
The bubbles coming out of the overflow tank, is air (combustion) pressure generated by the engine.
Then, the tank overflows; next time the engine is cold, needing more coolant, there isn't enough left in the overflow tank,
assisting in the overheating situation.( low level in rad.). Now that the rad is low, the air/combustion pressure can build up in the rad., until it blows out in the
overflow tank, unnoticed.???

You mentioned:" But I had heard this sound plenty of times before in the 4 years I have owned it. And it never overheated before."
I hope I'm wrong, but this "could" have been the start of an HG leak...
The most important denominator here, is the bubbles in the tank: where are they from? The rest is the resultant.

Good luck
 

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Discussion Starter #20
OK, here is the latest update. I haven't done anything since the last time it was in the shop. I just let my wife drive it and I've been keeping an eye on it. 4 weeks since last dealer visit and it hasn't overheated.

However -- I opened the hood today and looked at the overflow bottle. The coolant is about 3 inches from the cap. It has been slowly rising over the past month. I think what is happening is that there is some small pinhole leak in the system somewhere. My overflow bottle is almost full because a growing air bubble in the system is displacing the coolant. I suspect eventually the coolant system will burp a big bubble into the overflow tank and (since it's already full) coolant will blast everywhere just like it did before.

The dealer previously pressure tested the coolant system and the block. I know little about these tests. Did they not wait long enough to see the slow bleed in the system? Would some margin of bleed be expected during the test?

I'm going to try and bleed the system again and get rid of the bubble. Maybe replace that rad cap just for grins. And then keep watching. Of course, if you guys have any input...
 
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