Subaru outback overheating.

Car: Subaru, Outback, 1999 - Back to Fix-It - Subaru Repair Manuals

Q.Subaru outback overheating. Took to mechanic, did pressure check and found "hoses need replacing, radiator crack and thermostat replacement" Got work done.
Yes, they did add Subaru special additive. Drove away- car overheated to two line below redline.
Stopped car, small amount of leaking. Let car cool down, started up again and car didn't go past mid point.
Because afraid I could blow head gasket, left car at shop and had mechanic look at it again today.
They drove it, said it was fine. I left and again less than a mile away, gauge crept up to over midpoint but two lines below redline. Let car cool down, restarted and drove home with heater on high. car never went past midpoint on this trip.
No white smoke, no leaking, hoses didn't feel hot, heard fan kick on, no scum in water or on radiator cap. (Cap does appear to be old one) My mom says let car sit and have another shop look at it monday. Any ideas on why car is still doing this? Mom says maybe needs new cap or temp sensor.

I already checked/done: Aware of problems with this model but does not appear to be cracked block. Replaced radiator But does look like they used the old cap), hoses, coolent and had subaru recommended additive added, thermostat and gasket.
Driving home with heater full on car did not overheat or go above midpoint.

Answer HI there! It sounds like you may have the beginning of a head gasket problem.
The Subarus don;t actually leak coolant into the engine, rather the exhaust leaks into the cooling chamber.
This causes the coolant to become super hot in a big hurry. Usually 3 - 5 miles.
Take it to the new shop and ask them to test for hydrocarbons in the cooling system. I have done a bunch of these and it always starts this way. The best way to be sure is to check for hydro carbons. A pressure test dosn't normally show any problems. I have just seen this happen enough to let you know how to approach it.
Hope this helps!

Addition So you don't think it could be a bad cap, temp sensor or failed thermostat?
I don't understand a lot about subaru but since it didn't go above midline with the heater on I just question head gasket as a first choice ( but the testing for hydro carbons is a great thought.)

Answer It could be a bad cap although that would allow air into the cooling system.
I thought from your post that the thermostat had been done by the shop already, along with a new radiator and hoses.
Coolant temp sensor will set the check engine light normally. I would say check the fluid level and make sure it is full. Let me know.

Addition Yes the shop did replace the thermostat but I know even new ones can fail.
The radiator cap looks like its my old one but the hoses and radiator they did replace also.
Coolant level did not change in the drive home and remained full. Over flow also did not show any loss in fluid.
When you say a bad cap could let air into the system, would that cause it to "burp air" when sitting? Not sure what you mean or wwhat would happen if it is the cap letting air into the system.
Again- appreciate you patience !!!! I'm trying to figure this out. Its frustrating when you have a car with model history like the 2.5 L engines.
Any problem and everyone first says the head gasket. I don't deny this could be the problem but its kind of like going to the Dr for cold symptoms and having them check for cancer first.. ya know?

Answer OK. Air into the system will cause it to run warmer then usual.
I have never replaced a cap on a subaru. Like I said, I am not saying 100% that the cap isn't the problem. I am suggesting it be checked as I have seen it a bunch of times.
I had one that had a bad head gasket that I had to put 15+ miles on to get it to overheat.
My service manager was pretty ticked because I kept giving the car back without finding the problem. In the end, it was the head gassket.
I just could not see charging the customer big money for the head gasket job without being 100% sure.

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Subaru outback overheating.