2005 Subaru Outback XT overheating w/AC on

Hi everyone,

My wife has a 2005 Subaru Outback XT w/auto trans, about 135k miles. We live in SoCal.
The car runs great…well, most of the time. During the summer, or when driving up steep mountains with the AC running, the needle will climb steadily north towards overheating. Call me timid, but I’ve never been curious enough to find out what happens if I let the needle get into the red.
To let the needle drop, I have to turn the AC off. This isn’t the best option now since we’ve been experiencing over a week of temperatures higher than 103.
I also noticed that the temp needle will drop to normal within a couple of minutes if I turn on the heater.

I did open the bonnet when we returned from a trip and with the car running, checked to make sure both fans were running. They were.

So guys, what do you think? We are a Subaru family, and love this car. We’d like to keep it running for many more years.


The VERY FIRST thing I would look into is to see if your fans are turned on when you engage the AC…they should go on IMMEDIATELY upon pushing the AC button. If they do not come on…then this is your issue…could be a fuse or a relay as the culprit…or both. IF your fans are working…and you still get hot under the collar…the next item to simply replace is the thermostat …its an EZ job to do on that engine. IF this does not solve the overheat problem the next item on my list to look at/replace is the Radiator…another ez job to do yourself actually. Radiators DO GO BAD…I have replaced MANY of them due to symptoms like this and after I go thru a bunch of checks on my list when suspecting a radiator (using my infra red thermometer usually) it usually always solves any overheat issues. A Rad for that vehicle shouldnt be much more than about 150…and if you do it yourself…you save HUGE MONEY… So I would suggest you attempt it…it really is not difficult…but then again…Ive been doing this sort of thing over 25yrs now…so i may not be the best judge…lol…sorry

So…like I mentioned prior… when you have your AC on your cooling fans should immediately engage…The AC adds a fair amount of load to the engine (generating heat as a result) Its akin to driving up a steep grade hill… So…the fans need to be ON to help shed this heat…the engines thermostat needs to be functioning properly…and the Radiator has to have the ability to efficiently shed heat… It cannot be clogged up and operating on say 5 out of 20 cooling rows…the infra red thermometer with laser pointer is the trick gadget I use to see if the rad is functioning as it should…your hand also works…but is less accurate. Hope this helps


Overheating or near it is nothing to play with unless your want to turn an older vehicle into junk.

The cooling system is a relatively simple thing to get looked at, what is stopping you or you asking for DIY?

Radiator cap. Classic symptoms, cheap fix.

Thanks all for the comments. I swapped the radiator cap with my other Subaru, no change. The radiator was replaced last year. Both fans appear to be working with AC turned on; are they variable speed? I took it to one of the recommended mechanics and they couldn’t get the car to overheat so they had nothing to fix. :frowning:
It still runs too hot on very hot days or when driving up the mountains with AC turn on.

No, as far as I know, Subaru only uses single speed fans.
Are you sure the fans are both turning the right way? You did have the radiator replaced last year so maybe the connector got plugged in the wrong way. I think they’d have to work at being that stupid but one never knows…


One would imagine it would overheat all the time with a stuck thermostat, no?

Probably, but if it’s stuck partly open, maybe it’s a problem just under high load. Given the cap and radiator have been replaced, just searching for another cheap option. Next might be water pump.

Good point.

Both fans are set to blow air through the radiator, front to back. I’ll check the thermostat as well.

i think the cond. in front of the rad is stopped up bugs and dust will make it slowly over heat! Go to a car wash raise the hood and spray the cond out being careful not to fold the fins! this will solve your problem the air ways through the cond is very small and over ten to fifteen years the dust collects and restricts the air flow very cheep fix ( sorry about the spelling)

Didn’t have any problems over the winter and replaced the thermostat and several cooling lines which were getting old and brittle.

However the temp needle still crawls up though, as always, and doesn’t get into the red. Although I did notice that perhaps the exhaust is not breathing as well as it should, it seems to move as much air as my Subaru Legacy (same 2.5 engine w/turbo). So I wonder if the cats are starting to fail and causing the restriction.

According to the service manual, this is an area to be checked in case of overheating.



Connect a gauge and perform a backpressure test. Then you will have a definitive answer as to whether the exhaust is partially restricted

Since the radiator has been changed and the fans checked, I’m voting on the T-stat. It is not at all uncommon for a T-stat to not open fully, especialyl of the engine’s been overheated in the past.

Which bring to mind the question…was it? And are there any other operating symptoms?

I have the same problem on my 2005 XT. Almost overheated Tuesday when driving through Calabasas on the 101 up the hill when it was 100 degrees. First noticing this happening when heading up to Mammoth back in June. Had my radiator and thermostat replaced last month but, the car is still coming close to overheating when going up hills in hot weather.

Interesting comment about the exhaust. My check engine light just came on again after having replaced the o2 sensor in June. Maybe the two things are related…

Again, radiator cap. New radiators do not always come with a new cap and swapping an old cap from another subie is not a valid troubleshooting practice. A new cap costs what? $13? Get from a dealer.

BTW, I have a Saturn with over 260k miles. I mention this because up until this summer, the temp gauge has always stayed at two needle widths above the quarter mark, so steady you would almost think it was painted on. But this summer, I took a vacation and was visiting all the national parks and for the first time, my needle moved up past the half way mark on the gauge while climbing those mountains out there with the AC on. It didn’t do any damage, but it never got more than a needle width above half way, except when climbing the grade out of Death Valley, then it got two needle widths above half way. It was 121°F at the ranger station at Furnace Creek when we stopped there. Bad Water Basin felt even hotter.

Here is another test you can try. When it is hot, the needle up in your uncomfortable range, pull over if safe to do, immediately open the hood and have someone turn off the AC at that time and see if the fans stop as soon as the AC is turned off. If they turn off, then you have not reached the temp that the thermostatic switch is set to to turn them on. BTW, only one might come stay on if this temp is reached. Apparently in a Saturn, the fans do not come on (with AC off) until the gauge reaches the 3/4 mark.

Your car may not be getting as hot as you think.

Getting the fuel pressure gauge change today per the check engine light. Told this mechanic about the overheating problem when I go up hills on hot days. He said he has encountered Subarus with head gasket problems leaking gasses into the cooling system and he can run a test. He just called and said that this is indeed the problem and the head gasket will be several thousand to replace. Knowing that it is an eight year old car, he said it would probably be in my best interest to sell the car before next summer…

I found this other article that discusses 2000 era Subarus and head gasket issues and one of the symptom is over-heating in mountain driving…


The issue I have is your mechanic may be feeding your line of crud and is mistaken.

Subaru’s indeed are known for head gasket problems. However this is specific to the NON-turbo 2.5L and you have the rarer 2.5L turbo motor that is not known to have any sort of head gasket issues.

I would get another opinion as the mechanic may be throwing up his hands. Check out LegacyGt.com and see how many head gasket issues are posted. Nearly zilch.