Why is my car overheating

Is the radiator fan(s) working properly? When you turn the A/C on, does the fan(s) come on as well?

Based on past experiences and Subaru history - when a *mysterious* overheating problem occurs that just can't be corrected by conventional methods - it's usually a failing head gasket. Yes I read about the combustion leak test - that's not always conclusive .. There is 'possibly' coolant entering cylinder # 3 causing misfire - look for any sign of steam (white smoke) from tail pipe - video scope inserted into # 3 after overnight park may reveal coolant in cylinder. Good luck.