I have a 2001 subaru outback and appears to be leaking coolant from thermostat but not having loss of heat yet. Can gasket be replaced or do you have to replace whole thermostat? Also where can I find diagram of this area? Where the coolant leaves rad at bottom and goes to motor

I doubt it.
A faulty thermostat would cause the engine to overheat after a few miles of driving. A faulty cooling fan could cause the engine to overheat and also keep the ac from working.
A leaking head gasket could cause overheating, and loss of coolant, but would not affect the ac.

This is common issue early sign head gaskets failure for EJ251 SOHC engine for external coolant leak. Second gen 96-99 with EJ25D is worst because when head gaskets failed, it's an internal leak that allows coolant and oil mix together in the combustion chamber to destroy engine.
You can drive it for at least 6 months or more as long as you keep top up coolant since the leak should be small at a slower rate leak. I drove mine for a while before change head gaskets. You're looking at `$1000-1200 job a dealership since you might as well change the timing belt, water pump, idlers while engine is pulled to replace head gaskets.

Thermostat Stuck on warm up & or you have
a possible head gasket failure & I would suspect
a loss of coolant.

If that is the case, you have a ruined exhaust converter &
O2 sensors as well & a $5,000 plus repair bill coming

test the scanner and computer test for most effective result.
However see if fan/waterpump drive belt is slipping. Coolant is frozen
inlet or outlet water hoses are clogged or kinked. Coolant tube is blocked. Temperature gause is defective. Water pump defective. Fan is too far from radiator,(close it) .Defective water distribution tube. replace the tube. Fan insuficient blade are or pitch replace with large fan or with more blades.
God bless you

have your head gaskets and radiator checked

If you had to bleed the radiator, it is likely your head gasket is allowing exhaust gasses into the coolant. A symptom of this is the coolant reservoir may seem like it is filling up. The other item which is simple and cheap to replace is the radiator cap. If it is leaking, it will allow too much fluid and pressure out of the system and then the coolant will boil. If it is the head gasket, the repair is expensive, usually $700 or more.

I would have the head gasket checked.
When the engine is cold check the rad and overflow bottle.
These motors have a tendency to leak externally at the head gasket towards the rear of the engine.
Low coolant will cause over heating at the engine and loss of heat inside the car due to vapor locks.

I assume you have checked the cooling system to ensure that first that it is full and second that there are no leaks. Those pesky little bypass hoses tend to go hard and split if they are over 5 years old. The over heating could also be caused by a clogged radiator or a faulty water pump. If there are no leaks and over heating is accompanied by loss of coolant, then it could indicate a problem with the head gasket allowing very hot high pressure combustion gases into the engine water jacket which boils the water away.

Check the oil again. If the level is higher than it was after you changed it and/or is pasty again (kind of like milkshake) then you have coolant getting into it--most likely through a leaking or blown head gasket.

sounds like one of 2 things, the thermostat or the engine has a leaking head gasket, replace the T-stat 1st, if the problem persists have the engine tested for blown head gasket(s) if the radiator was the problem u would have circulation and engine would overheat very slowly or just hotter than normal.