When it is in the red, there is no heat. After 30 sec.-1 min. it returns to normal for a few minutes. It just started doing this, and the performance of the car does not seem to be affected by the flucctuations. Whats up?

Either it is very low on coolant(i know very obvious but worth mentioning) or you have a sticky thermostat. Either way get it checked/fixed right away. Subaru motors do not like to be overheated and are prone to cracked heads!

it is the fans
when you are still and they are not working the car will get hot.
and when you are moving you force air through by moving forward.
be sure the fas are coming on.
may also be not turning fast enough to cool. (old worn out motors)

You are low on coolant, or the thermostat is sticking shut (keeping the coolant inside the engine = no heat). If it were the fans, your heater would get hotter. Thermostats are cheap, and easy to replace. You need to fix this quick, or get a new engine.

l agree it is the fans or possibly a bubble in the cooling system. l had this problem after flushing mine my self and could not figure it out. Took it to a lube place ant they just ran the car with the radiator cap off and fiddled with the radiator hose and sure enough it burped and no more problem. But With the mileage you probably have you might have some electrical issues messing with the fans.

l had the same problem with my '93. The gauge shot up & not heat, until finally all the coolant leaked out of the busted radiator. After l changed the radiator & put in new coolant my engine was running hot with no heat. Turns out there was air stuck inside the system. l shut the car off & cracked the pressure cap WITHOUT REMOVING IT. The air left the system & now engine is cooling & heater is heating. Check for a bad radiator.
If there is air in the system, turn on the cold engine with the pressure cap off & let the air bubble out. That should fix it. Never remove the cap when the engine is hot.

Just normal, kept driving it until the coolant comes out, and your car is overheating because no coolant, fan is not working.

You should bring it to dealer to check it up.