Engine Cooling problem
1999 Subaru Outback 4 cyl All Wheel Drive Manual 163000 miles
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my outback overheating driving through the mountains in utah and I managed to get it to a town by stopping several times to let it cool down. Once there a shop in the town replaced the radiator and thermostat. But it has overheated twice since then (only a few days), both time while having the A/C on. I turned it off the first time and the temp went back to normal. The second time turned the ac and the car off for a few minutes. Now I don't know what it could be, maybe they didn't replace the thermostat, maybe there is gunk in it, no idea. Any ideas would be helpfull.

Have it block and pressure tested-do the block first to pinpoint a combustion leaking into the cooling system or a gas analyzer to sniff for hydrocarbons at the radiator fill neck.

Pressure test: do not do a pressure test if there's leakage at the headgasket this might cause coolant into the cylinders and lock it up or bend a connecting rod if cranked thereafter. The headgasket should be repaired before doing the pressure test.

If the block and pressure test passes check the following: ,Pressure test the Rad. cap,Clogged radiator,air lock in the cooling system ,Fan clutch,Radiator electrical fan,collaspe hoses,water pump.