Overheating on a 2001 Subaru Outback Legacy Wagon

So this car is having overheating problems – it’s a 2001, Subaru outback legacy wagon, 125,000 miles on it, automatic. I was driving it an hour on the highway, pulled off an exit, it overheated and stalled. Got it into a gas station only to find the coolant cap on the reserve had blown off and coolant went everywhere. So i put new coolant and water in and got it to go 20 minutes only to overheat again. Drove it back home blowing the heater and seemed to somewhat remain at 1/2 to 3/4 mark on the temp gauge. Then i took it to shop-- they said probably an air bubble that worked its way out?! and they basically did nothing. Drove it again an hour this weekend, same thing happened–drove it back with the heater on. Brought it to ANOTHER shop that first off thinks its the timing belt. The person i bought it from had head gaskets, timing belt, water pump and thermostat all replaced. The only thing they were told to do was flush the radiator which they did not do.

SO…what do i do? I’m taking it to yet another place and don’t want to be ripped off – Change the radiator cap? Could it be one of the parts blew again? They were replaced last year. Should i flush the radiator-- what would that do really? Could it be an electrical/fuse problem with the fans? Any help would be greatly appreciated. Thank you in advance.

Changing the radiator cap might indeed fix the problem, and is cheap to do, so that’s worth a try I think. I’d be inclined to change out the thermostat and flush the entire cooling system and refill with fresh coolant at the same time.

What to do if the symptoms persist after that depends a lot on this car’s history, esp its recent repair history.

Things that can cause overheating:

  • Cooling system has a leak and doesn’t hold pressure. Radiator cap could be the fault, or a cooling system leak. Have the cooling system pressure tested.

  • Radiator cooling fans not coming on when they should. Usually this symptom would only show up in stop and go traffic or idling for long periods, like waiting in line for a hamburger at the drive-through window.

  • Water pump failing. Ask the shop to check the water pump output flow rate.

  • Something is plugging up the cooling system inside the engine. Possible if a recent repair has been made, for example the mechanic allowed a rag to get sucked into the cooling system by mistake.

  • The radiator is plugged up. Have it flow tested by a shop.

  • Something is blocking air flow through the radiator. Ask for a look-see at the radiator grill area by a shop.

  • Thermostat is bad. Remove and test it in a pan of hot water to see if it is opening at the right temperature and is opening wide enough. (Don’t try to fix overheating by removing the thermostat, that often makes the problem worse.)

  • Exhaust gas is getting into the coolant. This would usually be due to a head gasket leaking. Look for bubbles forming in the radiator, or have a chemical test done on the coolant to see if there are signs of exhaust gas in the coolant.

Best of luck.

Thank you! Mechanics have been giving me a hard time about testing the thermostat. They say they can’t just do that, they would have to replace it. They said the same thing about the timing belt. Does that sound legit at all?

The mechanics are for the most part correct. It’s not economical for a shop to test a thermostat by putting it in hot water on a stove with a thermometer. Replacement thermostats don’t cost very much, usually less than $15. It is possible however to get a bad replacement thermostat, which is the reason I always test them myself before installing them as a DIY’er. But I don’t think shops do that as a matter of course. If you agree to pay them upfront for their time at the shop’s hourly rate, I expect they’d test it for you though. It would take maybe 30-60 minutes, so the charge would be around $50 to $100.

Timing belts aren’t tested either. There’s just no reliable way known. If its time for a new one, according to the mileage or time since the last one, they just install a new one. The experts here say a visual inspection isn’t a reliable way to ascertain a used timing belt condition.

Edit: Have any of the shops tried the manufacturer’s procedure to bleed the air out of the cooling system?

You are talking about one of the MOST infamous Head Gasket problem children out there. If you just purchased this vehicle then I don’t know what your options are here.

If you suspect that the thermostat is faulty…then just replace it…they cost about 12-20 bucks…and are extremely easy to do on this engine. The thermostat housing should be located right at the bottom of the engine in the front. If you lay down in front of the car and look at the engine you will see the thermo housing.

If you go and swap out the thermostat…you Must be very careful in how you refill the system. You dont want an air pocket in the system as this will create big trouble for you. You need to fill the system up fully…also fill the overflow reservoir to the top. I am uncertain if this engine has a coolant system bleed screw to “Burp” the air bubbles out of the cooling system for you like Honda’s tend to have. In lieu of a bleed nipple screw you need to run the engine till the temp needle gets toward the normal range and then shut it down and let the engine cool. This will allow the coolant to contract and pull in coolant from the overflow tank… Then you need to top off the overflow and the radiator again…and do the same thing… I would do about 3 Hot Cold cycles in order to get a nice solid cooling system that is full of coolant with Zero air pockets. Air pockets can cause you to have symptoms similar to what you are seeing and make you thing the Head Gaskets are bad and or the thermostat is faulty.

These engines do not respond well to being over heated…so don’t do that. Once over heated you will then need to suspect bad head gaskets and you really don’t want to go down that road.

Did the previous owner mention replacing the head gaskets? Was there some sort of work done prior to you buying this vehicle? It would be helpful to know these things. Not sure if you are aware of these vehicles reputations when it comes to head gaskets…but methinks you are not aware of this unhappy condition.


The person i bought it from had head gaskets, timing belt, water pump and thermostat all replaced. I wrote that in my post above but i’m wondering if it’s all going again. Thank you for your help.

Oh NO… You really need to get a handle on this overheating or you can easily throw all of that work in the garbage with one “Good” overheat…If the engine starts to go up into the beyond normal range of heat…Simply shut the engine OFF…Immediately.

You might want to look into the Subaru History with some of their engines and the Head Gasket issues they have been having. If your guy had them done previously…he surely used the updated Head Gaskets from Subaru…or My God I hope he did.

Don’t let this engine Overheat…its just that simple… It does NOT need to occur. I have never overheated a single engine in my life. We are talking about 50 different cars and trucks that I have driven over time.

If you think its the thermostat…Just replace it as cheap insurance. See what happens. Dont forget that Overheating can also be caused by cooling fans not working…But this is usually when you are stationary or idling a lot of the time. Radiators DO FAIL over time as well and they lose the ability to shed heat from the liquid…I believe they get clogged internally but outwardly look like they are fine. I have seen this happen many times. Radiators are not that expensive and are easy to replace as well.

I hope you go thru this process slowly and smartly and find the root cause without causing any major damage that will require new Head Gaskets. Let us know what you find


Oh god me too! I specifically bought this car BECAUSE of the replacements, but i’m pretty worried. I don’t know if he did the repairs well and now i’m fearing that he didn’t. The first mechanic said he didn’t see anything wrong at all (not being able to see the thermostat, timing belt, etc.) He said the fans turned on at the right time and the head gaskets looked good to him (at that time.) That’s why he thought it was an air bubble-- but that didn’t make any sense as he also didn’t bleed/burp the radiator. I forgot to mention the radiator had been replaced as well!

A thermostat can be tested when removed from the engine. Due to economics they’re usually just replaced unless it’s DIY situation.
The timing belt is not going to cause the overheating problem.

Does it overheat at idle and slow speeds or only at highway speeds?
Does the A/C have to be on before it overheats?

There are several ways this could go but I wouldn’t condemn the head gaskets just yet. I will advise that the car not be driven while in a badly overheated condition as Subarus do not take kindly to that.

The Head Gaskets “Looked Good To Him” Methinks if any mechanic said that to me…I’d have to take him round the corner and let him know a few things about engines. LOL I dont know why he would say that but… Who knows. I would do the things I outlined and see what you get…slowly and gently without overheating the thing. If you notice that there are ANY air bubbles bubbling up thru your overflow container when you are carefully heating up the engine…You can stop right there. That would indicate bad head gaskets. In fact one time on a Subaru…a mechanic told me that if you know the thermostat is good…the rad is good, fans etc are good…and you are getting an overheat… He told me that was the indicator alone of Head Gasket failure… I was puzzled at this as I usually need more clues… Like milky oil, Puffy white smoke out the tailpipe…and the dreaded Bubbles coming up thru the overflow due to the radiator getting over pressurized via head gasket failure and leaking compression into the water jackets. Yes you can feel the radiator hoses to see if they are getting sort of inflated like a bike innertube while the engine is running…this is a pretty concrete clue for a failed Head Gasket.

I hope the tests I outlined go smoothly for you… let us know. Not sure if you are doing the diagnostics yourself or what…but the ones I outlined are pretty basic to accomplish


I wish I could do the diagnostics myself! But I need a pro. I’m going to get it all checked out. Thanks!

It doesn’t overheat w A/c and doesn’t overheat while idle… Only highway driving.

Well…you can do the Hot Cold cycles I described above to burp out any possible air in the cooling system. You need to be sure that your rad cap holds pressure… Fill the Rad…Fill the overflow…make sure the overflow hose to the rad has no holes in it either and is firmly connected to the radiator. Then just heat up the engine…let it cool and watch it suck in new coolant… Also monitor the overflow for any air bubbles that may be present coming from the overflow hose into the container. You do NOT want to see constant air bubbles inside that overflow container.

This Hot Cold thing takes a while and may take about 3-4 cycles to fully burp out the air…but it works if you keep everything full of coolant…Have a good Rad Cap…and a good hose into the overflow. Skill level for this job is about a 1.5 so anyone can do it.


Before you dump anymore money into this, I’d suggest you have a pressure leakdown test done. Just because the headgasket was replaced does not meant the head wasn’t warped. It appears that the previous owner dumped this because he discovered it had serious problems, and you’ve acquired them.

As regards testing a T-stat, it’s easy to do and while it isn’t cost effective to test it normally in your case it’d be a good idea diagnostically… it can eliminate that as a possible cause. However, if it fails leakdown, and I suspect it will, it doesn’t matter anyway.

Post the results. We do care.

With everything that has been done and highway overheating only the suspect might be the radiator but seeing as how that has been changed the radiator option is out.

A head gasket issue could cause this but my preference is to not be too pessimistic about that for the time being.

Some options could be iffy fan operation. With the A/C ON both fans should be running so that is something you can easily check yourself. With the A/C OFF and the engine allowed to idle you should hear one of the fans cycling on and off as the temperature gets to the normal range.

Another and much more rare possibility could be a missing or damaged air deflector. This one is not specific for your car and serves only as an illustration.

Thanks so much everyone. Jury is still out. So I will let you all know soon!

So so far the shop has not found anything! They are a very reputable shop recommended on here. They did everything diagnostic except drive it an hour which they are kind enough to do tonight. They believe it’s a circulation issue. Sound familiar to anyone?

At 14 years old, it could very well be a circulation issue, specifically a gumped up radiator. In your first post, you asked what a radiator flush does. What is does is, using a chemical, attempt to clean deposits from the inside of the radiator core’s tubes. Deposits prevent and/or restrict the coolant from flowing through some of the tubes, reducing the ability of the radiator to dissipate heat. The very coating itself acts like an insulator and reduces the ability of the radiator to dissipate heat.

Another circulation restriction possibility is the radiator hoses themselves. The hoses are made of layers with a fabric core between them. Occasionally the inner layer (the liner) will separate from the outer shell and block the hose. This can be sensitive to heat.

Radiators can be “mapped” with an infrared thermometer, to see if there are areas not dissipating heat the way they should be, but I don’t think that idea even occurs to most shops. It should, but it may not. Hoses… if in doubt, change it out. Hoses are cheap.

The OP mentioned in one of the later posts that the radiator had been replaced as well and so was the water pump. That doesn’t leave many possibilities.

Erratic fan operation, new thermostat of dubious quality, missing air dam, etc.

Maybe the radiator pressure cap is weak and is burping some coolant out into the overflow tank which is then popping the coolant bottle cap (not the radiator cap) loose.
A new radiator should get a new cap but different shops have different methods.

Well, seems like the shop is going to replace the thermostat again bc it may have been put in wrong. They are also flushing the radiator for good measure. They cannot find a thing. They also said they drove it and it didn’t overheat with them and only went slightly above the half way point on the temp gauge. They are just doing what they can even though the radiator was switched out. At least they are certain that the head gaskets are not the problem! But i’m a little concerned that they are still confused.

At least they are doing something. That’s progress I guess. I don’t see how flushing the radiator will help, as it is a new one right? But no harm done.

When I test the cooling system in my Corolla after some cooling system change, the first thing I do is an idle test. I let the engine idle from cold in the driveway, and watch the temperature guage on the dashboard. The heater and AC are off. When the gauge needle gets about 50% up the scale, the radiator fan will turn on. Then the gauge will slowly go down until it is about 40% up the scale, at which time the radiator fan will turn off. I place little marks on the gauge display – at a time knew the cooling system was working correctly – so I know the proper switching points for the radiator fan. I also note how long it takes to go through this cycling and compare to what it is when the cooling system was known to be working. Usually it takes 5-10 minutes of idling from cold for the fan to kick on, then another 5 until it turns off.

If it passes that test, I’ll take the car for a drive at around 40 mph, and note where the gauge reads. It will hone in at the mark I placed there before, the nominal temperature for high speed driving. If it passes that test, I’ll repeat this, but driving on the freeway at 65 mph. And include some uphills. The gauge should stay very close to that same spot, climbing neither much higher, nor much lower.

For me, if a test fails, it is always the first test, the idling test. It has never passed the idling test and then failed the driving test.