I have a 2003 outback wagon with about 195,000 miles on it.
It is my wife’s car so I don’t drive it much. 
She was about 60 miles from home the other day when it overheated, she said
gauge was close to the red.  She pulled
into a service station and the guy added about half a gallon of coolant which brought
the temp back down and she drove home after that with no problems.

I got a pressure test kit from Advanced and pumped up to 17

psi and it held for over a half an hour. 
I can see no visible signs of leakage. There is no water in the oil and
I did a test with the pressure tester hooked up with the motor running and had
someone rev the engine.  The gauge did
not go up.  So I think a head gasket is
not blown.

Any ideas how the coolant level could get that far down with

no sign of a leak?  I’m planning to drive
it kind of locally for a while and check the level often and see how it goes.

Well on possibility is that engine's head gaskets would have been prone to the external peeping leak. On my '00 it would just loose a little bit now and then but it didn't drip continuously. Keeping the overflow nice and full and making sure the radiator was kept full let me drive it that way for years. But if you don't check the level often to top it off then it will eventually get low enough to start overheating. And overheating is of course bad. There is a coolant conditioner that can be added that may help with this type of leak.

Leaky radiator cap that was fixed by removing and re-installing?

 

Are there signs of dried coolant anywhere?

 

4 or 6 cyl?

well the cap removing and re-installing is an interesting idea, but I do not see any evidence of dried coolant.  4 cyl.  Been driving it around locally all day level is still right where i t should be.

I have been driving the car locally for a number of days now and can see no loss of coolant.  If the coolant does start to go down is there a stop leak or conditioner brand that would be recommended.  I know some types of stop leak can cause more trouble than it solves. I'm from the Barrs era so there must be something more advanced than that.  I'm going to take the car on about 70 mile round trip today that involves going up a modest mountain and I'll see how that goes.

Those engines tend to lose coolant slowly, over a long period of time, due to minor seepage from the head gaskets. You'll probably never see a drip on the ground or anywhere under the hood because it evaporates away before it collects enough to drip.

 

Subaru recommends the use of their Cooling System Conditioner in all of the 2.5 engines from 99-up. It's basically a stop leak product. You drain the cooling system, add in the conditioner, and refill with Subaru coolant. Run the engine to operating temp for about an hour so it fully dissolves and works it way through the whole system. Costs less than $5 at the dealer.

 

Subaru recommends the use of their Cooling System Conditioner

 

Yes, add this right away.  A number of posters have said that it does no harm and can actually stop an outside leak for quite a while.  I have an 02, and I wouldn't think of not using it.

 

Thanks for the feedback.  I called my local dealer the other day and asked if there was a Subaru specific conditioner/stop leak that they sold.  They said no.  I'll call again now that I know it does exist and will give it a try once it warms up around here, hopefully later next week.

 

Thanks for the feedback. I called my local dealer the other day and asked if there was a Subaru specific conditioner/stop leak that they sold. They said no. I'll call again now that I know it does exist and will give it a try once it warms up around here, hopefully later next week.

ask for Subaru coolant conditioner.

http://www.amazon.com/Subaru-SOA635071-Coolant-System-Conditioner/dp/B00IGZP2UE

Thanks for the link.  I called my local dealer back and asked again about the conditioner.  This time they said they had it, cost 6+ bucks.  Went to the dealer and paid 2.76 for it.  go figure.  The coolant level has not dropped in about two weeks of driving since the overheat and refill.  But I'm going to add the conditioner this weekend, supposed to warm up.